1 ICHTHYOLOGICAL ECOREGIONS OF ARGENTINA(*) 

 
Hugo L. López1,2, Cecilia C. Morgan1 & Marcelo J. Montenegro1x 

1 División Zoología Vertebrados, Museo de La Plata, Paseo del Bosque s/nº, 1900 La Plata, 
Argentina. ProBiota. 

2 Comisión de Investigaciones Científicas de la Provincia de Buenos Aires (CIC). 
3 Instituto de Limnología “Dr. Raúl A. Ringuelet” (ILPLA), CONICET-UNLP. 

 

INTRODUCTION 

The Argentine Republic is situated in the southernmost portion of the American 
continent, occupying over 2,785,600 km2 not including the Antarctic territory. The country 
ranges from subtropical areas (21º46’S) to subantarctic regions (55º03’S), extending 
latitudinally over about 4,000 km. It possesses significant latitudinal and altitudinal variation 
(33º of latitudinal range, and heights from Bajo de San Julián in Santa Cruz province at 105 
m below sea level, up to Mt. Aconcagua,  6,959 m over sea level), as well as two gradients of 
physical variability, extending in north-south and east-west directions. Owing to these 
features, the country presents a wide range of climates and soil types, being one of the 
countries with greatest diversity of biogeographical units (Lean et al., 1990, In: Bertonatti & 
Corcuera, 2000). 

There are four main hydrographic systems: Río de la Plata basin, the Atlantic and 
Pacific drainages, and several endorrheic systems. Within these basins, the ichthyofaunistic 
assemblage is well represented, with different magnitude in accordance with the different 
taxonomic groupings and regions considered.  

From an ichthyogeographic standpoint, and according to the works of  Ringuelet (1975) 
and Arratia et al. (1983), Argentina is included in the Brasilic and Austral Subregions. The 
first of these is represented by two domains: the Andean Domain, comprising the 
southernmost portion of Titicaca Province, and the Paranensean Domain, including part of 
Alto Paraná and Paranoplatensean Provinces. The Austral Subregion is represented in 
Argentina by the Subandean-Cuyan and Patagonian Provinces.  

The present survey indicates that there are about 441 fish species in Argentina, 
distributed throughout the country; this number represents less than 10% of the total fish 
species occurring in the Neotropical Region. There is a recognizable  trend of faunal 
impoverishment, both in North-South and East-West direction,  reaching its maximum 
expression in the provinces of Tierra del Fuego (situated at approximately  52º30’S to 55ºS, 
and 65ºS to 68º50’W) and San Juan (approximately 28º50’S and 67ºW to 70º45’W), which 
have 4 and 5 fish species respectively. In north-south direction, one of the regional indicators 
of this phenomenon is the Salado river basin in Buenos Aires province, which constitutes the 
southern distributional boundary for the majority of the paranoplatensean ichthyofauna; 12 of 
the families occurring in the Paraná-Plata system are absent from this pauperized 
paranensean ichthyofaunal assemblage. 

Most of the continental fish fauna of Argentina belongs to the primary division of Myers 
(1949), while some elements are included in the secondary division and others in an 
amphibiotic or ‘marine penetration’ category. This ichthyofaunistic scope encompasses a 
wide range of morphological, biological, ecological and ethological types (benthic and 
                                                 
. 
e-mail: hlopez@museo.fcnym.unlp.edu.ar 
 (*) This work was made as part of the project Freshwater Ecoregions of the World, Conservation Science 
Program, World Wildlife Fund,  USA.  A Spanish version of this document is in press by Comisión Administradora 
del Río Uruguay (CARU).  
 

1   

mailto:hlopez@museo.fcnym.unlp.edu.ar
mailto:hlopez@museo.fcnym.unlp.edu.ar


 

pelagic, migrating and sedentary, haematophagous or parasites, annual species, inhabitants 
of plains or heights, estivation-adapted, etc.) inhabiting different regions within the national 
territory. 
 
MATERIALS AND METHODS  
 

In this work we have adopted the ichthyogeographic proposals of Ringuelet (1975) and 
Arratia et al. (1983), which in general terms are coincidental with the Argentinian 
geographical regions, and the hydrographical scheme of Mazza (1961), excluding from our 
study the Pacific drainage basins. In addition to these, we referred to the works of Menni et 
al. (1996), Arratia (1997) and Dyer (2000). For background on the ichthyofaunistic 
composition of Argentina we considered López et al, (1987), and we consulted various 
sources such as Ringuelet et al. (1967), the bibliographical references in López et al. (1981, 
1982, 1987, 1989, 1991, 1993, 1994) and Ferriz et al. (1998), as well as Malabarba et al. 
(1998)  and various regional and reviewing works that are mentioned in Additional 
Bibliography.  

With respect to environmental protection and conservation, we considered the works of 
Chébez (1994), Bello and Úbeda (1998), Pascual et al. (1998), Bertonatti and Corcuera  
(2000) and López (2001).  

For the delineation of the ecoregions (figure 1) we performed a similarity analysis of the 
previously delineated hydrographical basins, using all the documented records of fish 
species as characters (Table 1). Table 2 shows the fish families present in each basin as 
well as their total number. The exotic fish species present in Argentina (Table 3) were not 
included in the analysis, and neither were some native species which have been spread by 
anthropogenic action (namely, Odontesthes bonariensis, Jenynsia multidentata and 
Cnesterodon decemmaculatus). The records that appeared doubtful as to the identification of 
the species or localities were also dismissed. The similarity analysis was performed applying 
Jaccard association coefficient and UPGMA clustering with NT-SYS program to obtain the 
resulting phenogram. The outcome of this analysis, along with other considered elements 
such as distinctive features of the systems’ dynamics, ecological determinants, and 
processes of environmental degradation occurring in each of the considered areas, were the 
basic elements used in the delineation of ecoregions.  

In the discussion of each ecoregion we have included the number of fish species for 
each basin, and the percentage that each represents in the total 441 species considered for 
the analysis (Table 1) is indicated in parentheses.  

In the last part of the characterization of each ecoregion we indicate the corresponding 
category in the classification of wetlands of Argentina (Canevari et al., 1998), the ecoregions 
of Argentina as delineated by Burkart et al. (1999) and the zoogeographical regions of 
Ringuelet (1961). In the cases where we have  tentatively extended the ecoregions into 
neighboring countries, the description of the ecoregion and all numerical data (including 
surface area) correspond exclusively to the Argentinian portion.  

With respect to the bibliographical references, we have listed separately the works 
mentioned within the text from the additional bibliography.  

 
RESULTS 

1) MISIONERAN ECOREGION 
Limits 

The ecoregion is limited to the N by Iguazú river; to the W by Paraná river; to the  E, by 
Uruguay river; to the SE it abuts on Lower Uruguay River ecoregion; to the SW, by the 
courses of two creeks, Itaembé creek (tributary of Paraná river) and Chimiray creek 
(tributary of Uruguay river), both included in this ecoregion, and by means of an imaginary 
line running between their headwaters.   

We have extended tentatively this ecoregion outside Argentinian territory to encompass 
neighboring areas in Brazil and Paraguay which are drained by tributaries of Paraná and 

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Uruguay rivers.  
Description 

According to Popolizio (1972) it’s a plateau with “subhorizontal tabuliform structure”, 
with a dorsal ridge formed by the orographic systems of San José, del Imán or Itacuara 
and the Misiones sierras. The fluvial system arises from this mountainous ridge and its 
spurs, and the streams descend on either side of the mountains to flow into Paraná and 
Iguazú rivers (western slope) and Uruguay river (eastern slope). These courses present 
many waterfalls originated in by basaltic rock exposures, and among these, the 
outstanding Iguazú Falls, falling in an arc of  approximately 2,700 m of which 2,100 are 
within Argentina and 600 m correspond to Brazil.  
Surface area: 29,801 km2 (all of Misiones province) 
Main basins: rivers Iguazú, Paraná and Uruguay, which form the natural boundaries of 
Misiones province, along with an important interior hydrographic network; some streams 
belonging to the Paraná river basin are Uruguaí or Marambas, Piray-Guazú, Cuñapirú, 
and Yabebyrí creeks, and some from Uruguay basin are Pepirí-Guazú and Yaboty rivers, 
and Persiguero and Chimiray creeks. 
Terrestrial habitats 

The rainforest’s floristic richness goes unparalleled in Argentina. The contrast between 
the greens of the forest and the remarkable reddish lateritic soils is the main feature of 
Misioneran landscapes.  
Freshwater habitats 
Alto Paraná river: in this sector of its course, the flood plains have scarce to moderate 
development, and they are under the  influence of the dams Yacyretá (in Argentina) and 
Itaipú  (in Brazil). The margins accumulate deposits of sandy sediments, loose and little 
cemented (on the right-hand or western margin) or gravel and sandstone deposits (left-
hand or eastern margin).  
Uruguay river: this river is the easternmost in the Río de la Plata basin. It extends along 
1,850 km and drains an estimated area of 365,000 km2. It will be described in the Lower 
Uruguay River ecoregion. 
Iguazú river: its course runs in overall E-W direction and is 1,320 km long. It’s one of the 
longest tributaries to Paraná river within Brazilian territory; the Iguazú or Santa María Falls 
are situated 28 km upstream from its mouth.  
Biodiversity 
Alto Paraná river: 217 spp (49.2%) 
Tributaries of Paraná river in Misiones: 62 spp (14,1%) 
Iguazú river: 45 spp (10.2%) 
Uruguay river: no precise data for the main course in this ecoregion 
Tributaries of Uruguay river in Misiones: 15 spp (3.4%) 
Occuring families: Table 2 

This ecoregion comprises the Argentinian portion of Alto Paraná Province (Ringuelet, 
1975),  with endemic species such as Oligosarcus menezezi, Bryconamericus sylvicola, 
Astyanax ojiara,  Bryconamericus agna, Gymnogeophagus che, ”Cichlasoma” tembe, 
Pimelodus absconditus and  P. mysteriosus as well as other endemic species that occur 
in the Brazilian sector of Iguazú river and haven’t yet been recorded for Argentina 
(Table 5). 
Ichthyofaunistic remarks 

The absence of certain groups which are of common occurrence in the Paraná basin 
(i.e., Miliobatiformes, Clupeiformes, Pleuronectiformes, and some Characiformes and 
Siluriformes such as Piaractus, Brycon, Serrasalmus, Paulicea, Pseudoplatystoma, etc.) 
in the interior water courses of this ecoregion seems to indicate that certain features of 
these courses, such as the presence of waterfalls of diverse magnitude, represent a 

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natural barrier to the distribution of fishes and have fostered the existence of endemisms 
such as those mentioned above. 
Vulnerable species:  ornamental fishes collected for commercial purposes (aquarism) as 
well as those species used as live bait. There in no legal regulation or any type of control 
respecting these activities. 

Biological value 
The outstanding feature is the riparian forest which grows along river courses forming a 

strip of varying width; this biological  formation presents a marked reduction of species 
richness in a general downstream direction.  

This ecoregion includes at least six areas considered as “areas of outstanding 
biodiversity” according to the criteria of Fundación Vida Silvestre Argentina (Bertonatti & 
Corcuera, 2000). 

Impacts/Threats 
Modification of water courses, dams and hydraulic activities, habitat fragmentation, 

poaching, inadequate management and destruction of the natural vegetation of the basin. 
This is an area of high anthropogenic impact due to the influence of the dams, both 

active and projected. Exotic species such as Cyprinus carpio (Table 3), the possible 
spread of Plagioscion squamosissimus which has been introduced in Itaipú impoundment, 
and the presence of species of Tilapia in some interior watercourses in Misiones (R. 
Filiberto, pers. comm.) represent yet another threat to the natural aquatic communities.  

National Protected Areas 
Iguazú National Park. 
San Antonio Strict Natural Reservation 

Ramsar Sites 
None 

Correspondence 
Wetlands: Region 1 (Río de la Plata basin), in part. 
Ecoregions: Paranense 
Zoogeography: Subtropical Domain (Misioneran District) 

Rationale 
The elements that validate the proposal of this ecoregion are the following: 
• This is one of the areas with higher number of ichthyofaunistic endemisms in 

Argentina (Table 6);  a great proportion of these occur in the interior watercourses 
of the territory. 

• Absence in these smaller watercourses of some families which are common in the 
large rivers (Paraná and Paraguay) 

• Anthropogenic influence, manifested mainly as deforestation, agricultural practices 
and impoundments. An example of this last factor is the great mortality of fishes 
that has occurred repeatedly in Yacyretá due to “bubble disease” (Domitrovic et al., 
1994; Bechara et al., 1996). 

 

Relevant Bibliography 
López (1992); Lucena & Kullander (1992); COMIP (1994); Sevori & de Moura Cordeiro 

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(1994); Azpelicueta (1995); Casciotta et al. (1995); Gómez & Chébez (1996); Miquelarena 
& Protogino (1996); Garavello et al. (1997); Miquelarena et al. (1997); Rolón & Chebez 
(1998); Braga (1999); Roa & Permigeant (1999); Azpelicueta & García (2000); Casciotta 
(2000); Miquelarena & Bockman (2000); Miquelarena & Fernández (2000); Azpelicueta & 
Almirón (2001); Blanco & Parera (2001); Oldani et al. (2001); Giraudo et al. (En prensa).  

2) SUBTROPICAL POTAMIC AXIS ECOREGION 
Limits 

To the N with Paraguay (tentatively, it would also encompass neighboring areas of the 
Paraguay river basin - see figure 1) and with the Misioneran ecoregion; to the W, with 
the Eastern Paranoplatensean ecoregion by an imaginary line that falls approximately 
over the 61ºW meridian, excluding the area of marshes in western Chaco province (see 
figure 1), and encompassing all the tributaries of Paraná river, including the middle and 
lower course of Carcarañá river, as well as diverse water courses that flow directly into 
Río de la Plata; to the E, with Lower Uruguay River ecoregion; to the SW with Salado-
Vallimanca ecoregion and to the SE with the maritime front.  
Description 

This ecoregion includes the area drained by the lower third of the course of Pilcomayo 
river, the lower course of Paraguay river and the entire Bermejo river basin, the area of 
sloughs and marshes in Chaco, Formosa and Santa Fe provinces, the Riachuelo basin 
and Iberá system in Corrientes province, the Corrientes river basin, the area of 
Submeridional Lowlands and the alluvial plains of Middle and Lower Paraná river, the 
Paraná Delta and the Río de la Plata river up to its limit with the maritime front. 
Surface area: approximately 375,700 km2. 
Main basins: Besides the mentioned watercourses, the diverse wetlands, which comprise 
rivers, creeks and slow-draining water bodies that form marshes and sloughs, are of great 
magnitude and hydrological complexity; the precipitations and regional floods, arising 
mainly in the Paraná and Paraguay systems but also in Bermejo and Pilcomayo rivers, 
also contribute their waters to these lentic water bodies.  

The zone of Submeridional Lowlands is situated between the provinces of Chaco and 
Santa Fe, in a vast land depression subject to annual flooding pulses generated by local 
precipitations and waters contributed from peripheral areas; this area has a poorly defined 
hydrographical network comprising for the most part shallow lagoons. It has  two sectors: 
the Northern sector features ravines and marshes, while the Southern one is dominated 
by the salinization processes derived from the high saline concentrations present in both 
surface and phreatic waters. A system of lagoons that drain largely into the Salado del 
Norte river through small watercourses lie across the eastern edge of the area.  

The Delta is the tide-free sector of Paraná river. It receives numerous tributaries, such 
as rivers Luján, Sarmiento and Carapachay and smaller watercourses.  

Terrestrial Habitats 
Part of this ecoregion belongs to the ‘Chaco Oriental’ (Cabrera & Willink 1971), which 

also receives the name of ‘Chaco de esteros, cañadas y selvas de ribera’ because of the 
abundance of wetlands. 

The main landscape includes savannahs of tall grasses, palm-tree forests, marshes 
and sloughs, broken by small hardwood ‘islands’ in more elevated areas. This landscape 
is the result of processes of fluvial and fluvio-lacustrian modeling. 

In the Deltaic area the growth of the vegetation depends on the wetlands, and an 
impoverished prolongation of the Paranensean Rainforest known as Riparian Forest 
(‘Selva Marginal del Plata’)  reaches the locality of Punta Lara in Buenos Aires province. 
Within the delta the dominating formation is ‘pajonal’ (communities of  Scirpus giganteus), 
along with some exotic species and, in smaller proportion, native willows (Salix 
humboldtiana) and ceibos (Erythrina crista-galli), as well as some endemic plant species. 

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Aquatic Habitats 
From a hydrographical standpoint, there are six distinct areas:  

• The zone of Chaco-Formosa marshes and sloughs:   with a surface area of 
approx  70,000 km2, it extends within the following limits: to the N, Pilcomayo river; to 
the W, a line running from Fortín Leyes (Formosa province) through  Villa Ángela 
(Chaco Province) up to the political borderline between the provinces of Chaco and 
Santa Fe; to the E, Paraná and Paraguay rivers; to the S, Tapenagá river. This area  
possesses an hydrological system formed by two autochthonous rivers which run in 
N-S direction, and also receives waters from two allochthonous courses, Pilcomayo 
and  Bermejo rivers, which arise in Andean regions. 

• The area of marshlands and sloughs in Santa Fe province: situated north of the 
lower course of Carcarañá river basin, it includes the so-called  “Submeridional 
Lowlands” (“Bajos Submeridionales”). Its limits are: to the N, Tapenagá river (border 
line between the provinces of Chaco and Santa Fe); to the W,  a line following the 
political border between Santa Fe province and  the provinces of Santiago del Estero 
and Córdoba, and to the S, the prolongation of this same line separating this area 
from Carcarañá river  basin. The Salado del Norte river forms an independent basin, 
which enters this region from Santiago del Estero. Surface area approx. 170,000 km2. 

• Alluvial valley of Middle and Lower Paraná river course: begining near  the 
confluence of Paraná and Paraguay rivers, this valley lies on the right-hand margin in 
the Middle Paraná course, and on the left-hand margin in the Lower Paraná course. It 
reaches the beginning of the Paraná delta, with which it intertwines in an elongated 
complex formation. The fundamental feature of the flood plains is precisely the 
periodical flood cycle, caused by the yearly swellings of the river, so that the changes 
in the physical and chemical features of the environment produce a characteristic 
response in the biotic communities. 

• Iberá system and Corrientes ríver: the Iberá system crosses diagonally the 
province of Corrientes, and it has a surface area of 12,000 km2. It is a vast plain with 
very slight south-oriented slope, and its shallow basin is fed primarily by rainfall. The 
system drains into Paraná river through Corrientes river. It comprises a complex 
association of lentic and lotic environments which become intertwined in vast areas of  
interface. There are lagoons that communicate with each other and with the sloughs 
and marshlands through  well-defined and active canals and finally conform a diffuse 
system that drains into  Corrientes or Corriente river. The latter is the final collector 
for Iberá system; it runs in a general NE-SW direction  and flows into the Middle 
Paraná course. Although this river is the only watercourse that drains the Iberá 
system, the location of Miriñay river, whose headwaters are in the immediate vicinity 
of Iberá, suggests the existence of some connection in past times.  

• Paraná Delta:   it forms a markedly elongated area with an extension of approx.  320 
km, reaching to the beginning of the Río de la Plata with a width of little more than  60 
km and representing a total surface area of approx. 14,000 km2. It extends 
approximately from  Villa Constitución  (Santa Fe province), at the origin of Paraná 
Pavón river– although some authors place its northern limit in the town of Diamante 
(Entre Ríos province), in an area called ‘Delta Viejo’ (Old Delta) (Vega, 1995) – up  to 
the place where Paraná Guazú flows into Río de la Plata. The Paraná river 
contributes the  sediments which form the homonymous interior delta.  Several rivers 
and canals separate a multitude of elongated islands and natural levees 
(“albardones”), formed by the silts deposited by the swelling waters, along with tree 
trunks, branches and water hyacinths that also contribute to the formation of the 
islands. Each of the islands is, according to Difrieri (1958), a basin full of mud where 
rushes (Scirpus californicus) ditch reeds (Phragmites australis), andf 'achiras' (Canna 
sp.) thrive. Vast  associations of  reed mace (Zizaniopsis bonariensis) and 'pajonales' 
(Scirpus giganteus) extend along the coasts and compact masses of rushes take root 

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in the shallow depths.. In general terms, the low easily-flooded areas occupy 80 % of 
the surface area, whereas the natural levees (‘albardones’) or non-flooded areas take 
up 20 %.  The delta holds a vast network of artificial canals that facilitate the drainage 
and navigation in the more populated area of the system.   

• Río de la Plata: this river is actually the estuary of rivers Paraná and Uruguay and it 
extends over an area of nearly 30,000 km2. It runs from Paraná delta and the mouth 
of Uruguay river, reaching the ocean in a 250 km-wide front after a 300-km course. 
The Río de la Plata hydrographic system  comprises all the tributaries of Paraná and 
Uruguay rivers, the main stems of these rivers, the Río de la Plata itself and some 
smaller streams that flow directly into Río de la Plata on both margins. Although the 
influence of marine waters reaches the vicinity of La Plata city (62º36’S, 62º12’W),  
the effect of oceanic tides is felt as far into the river as the north of Buenos Aires 
province, on the coasts of Paraná river,  and north of Entre Ríos city, on the coasts of 
Uruguay river. The course of Río de la Plata can be divided in  three zones: internal, 
intermediate and external. The internal zone is the area of the river headwaters, 
where the subfluvial delta is located; the oceanic influence is reflected basically in the 
tides that affect the whole river; the organisms living in this sector are typical 
freshwater forms. The intermediate zone stretches from an imaginary line extending 
between the cities of La Plata (Argentina) and Colonia (Uruguay), to another line 
uniting  Punta Brava (Uruguay) and Punta Piedras (Argentina); here the sea influence 
is noticeable; there are some marine fish species which enter the brackish low salinity  
waters; on both river margins there are low floodable coasts occupied by crab 
colonies ('cangrejales') (species of genera  Uca, Chasmagnathus and Cyrtograpsus). 
The external zone comprises the area of the river habitually demarcated by an 
imaginary line uniting Punta Brava and Punta Piedras and, in the outer limit, Punta 
del Este (Uruguay) and Punta Rasa, Cabo San Antonio (Argentina); this is the 
estuarial sector, with brackish waters where the greatest changes in salinity are 
recorded.  

Biodiversity  
Lower Paraguay river: 60 species (13.6%). 
Middle and Lower Paraná river: 188 species (42.9 %). 
Marshes of Santa Fe province: 90 species (20.4 %). 
Marshes of Chaco and Formosa: 87 species (19.7 %). 
Paraná river Delta: 164 species (37.2 %). 
Río de la Plata and tributary watercourses: 152 species (34.7 % ). 
Occurring families: Table 2. 

This is the area of greatest ichthyofaunistic diversity in Argentina, where most of the 
families belonging to the dominant groups (Ostariophysans), as well as lungfishes 
(Lepidosirenidae) and  groups of marine origin (Clupeidae and Engraulidae, 
Atherinopsidae, Belonidae, Sciaenidae, Achiridae and Potamotrygoninae) occur. Within 
this assemblage different  ecological, morphological and ethological adaptive features 
may be observed, and there are some remarkable migratory species  (e.g. the ‘sábalo’, 
Prochilodus lineatus, the ‘dorado’, Salminus maxillosus, and the ‘surubí’, 
Pseudoplatystoma spp.). The first of these is iliophagous and is one of the most important 
species in the bioeconomy of the system, comprising more than 50 % of its total biomass; 
it is the typical forage fish for large ichthyophagous species. There are also fish species 
that inhabit the marshes, sloughs, ox-bow lakes, rivulets, meander plains, etc.    

There are endemic species such as Ixinandria steinbachi, Hypostomus laplatae, 
Rhamdella jenynsi, Parapterodoras paranensis, Hyphessobrycon igneus, 
Hyphessobrycon wajat, Phallotorynus victoriae  and Megalebias elongatus (the latter is an 
endemism shared with Salado-Vallimanca ecoregion) (Table 6). 

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In this area the latitudinal pauperization of the Paranoplatensean fauna becomes 
apparent; but, on the other side, there are a number of occasional marine species 
(Table 7) in the outer margins of Río de la Plata estuary, among which are  members of 
families Ariidae, Mugilidae and Engraulidae that perform regular migrations, as well as 
some species that approach the coast to spawn (e.g. Pogonias chromis, Mugil sp.). 

Within Iberá system, the greatest concentration of species occurs in the areas of 
greatest development of submersed plants.  

The fish families present in the areas of  Paraná Delta and Río de la Plata are very 
similar, with some differences at species level (Table 2).  
Ichthyofaunistic remarks  

Some of the emblematic species or Argentina, such as dorado (Salminus maxillosus) 
and surubí (large cat-fishes) (Pseudoplatystoma spp.) may be found within this 
assemblage, as well as a great number of  ‘ornamental fishes’ and ‘miniature fishes’. This 
region is also inhabited by  some of the largest members of the freshwater ichthyofauna, 
such as manguruyú (Paulicea luetkeni). 

Bonetto et al. (1989) state that the icthyofauna of Iberá system is in some ways similar 
to the fauna from Riachuelo river (Corrientes), and  that within this assemblage two major 
groups of fishes may be recognized: north of Iberá lagoon there is a Northern sector with 
an essentially sedentary fish fauna, while the Southern sector is distinguished by the 
occurrence of Paranensean species that reach Iberá system through Corrientes river; 
these two groups are not clearly differentiated. One of the most remarkable shared 
features of these systems is the great abundance of piranha (Pygocentrus nattereri and 
Serrasalmus spilopleura). 
Vulnerable species: numerous ornamental species belonging to different families, such 
as Gymnocorymbus ternetzi, some species of Corydoras, Hyphessobrycon and 
Lepidosiren paradoxa (only small juvenile specimens of the latter species are 
commercialized), species commercialized as live bait (Gymnotiformes, Characiformes and 
Synbranchiformes), annual fishes (family Rivulidae), vulnerable because of their particular 
breeding requirements and also because they often inhabit man-made wetlands,  
“miniature fish”,  mostly  Trichomycteridae, which are poorly known forms, less than 20 
mm long. In addition to these, the sea catfish (Netuma barbus) that performs anadromous 
migrations.  

Biological Value 
One of the remarkable features of the ecoregion is the riparian rainforest that grows 

along the hydrological system, with decreasing species richness  in north-south  or 
downstream direction.   

The area of the alluvial valley of Middle Paraná river has special features, being a 
trophic and breeding area for various migratory species.   

According to Bonetto and  Hurtado (1998), the fishes that traverse the deltaic area do 
so only sporadically. On the other hand, important concentrations of silverside (‘pejerrey’) 
(Odontesthes bonariensis) congregate in lotic areas of the lower delta and migrate early in 
the year (autumn-winter) up the Lower and Middle course of Paraná river, where they are 
presumed to spawn in brackish waters connected to the Middle Paraná course. The Delta 
is also the southernmost refuge for the Marshes Deer (Blastoceros dichotomus) and the 
river otter (Lontra longicaudis). 

From hydrological, physical and biological standpoints, the estuary of Río de la Plata is 
a complex system, where singular biological and migratory phenomena occur.  In 
Samborombón bay (Buenos Aires province) two reproductive strategies have evolved 
among fish species: the “estuarial spawning” species use this environment as spawning 
area (e.g. Brevoortia aurea, Odontesthes argentinensis, Odontesthes incisa), while the 
“estuary-dependant” species spawn in high salinity waters (e.g. Mugil liza, Pogonias 

8   



 

chromis, Micropogonias furnieri, and some Pleuronectifrmes) (Lasta, 1995).  
According to Bertonatti and Corcuera (2000), within this ecoregion there are “areas of 

outstanding diversity” representative of different biomes: Chaco Húmedo, Espinal, 
Pastizal Pampeano and Delta e Islas del  Paraná. 

Impacts/Threats 
Similarly to the first ecoregion, this area faces threats such as alteration of water 

courses, dams and hydraulic works, habitat fragmentation, poaching, inadequate 
management and destruction of vegetation of the basin, resource overexploitation, 
advance of agropecuary activities, unregulated tourism/recreation, fluvial transportation, 
as well as  the existence of urbane concentrations, with the accompanying industrial and 
portuary activity, and presence of nuclear and hydraulic centrals. An additional element  is 
the presence of exotic species such as Cyprinus carpio, Acipenser cf. baeri and 
Hypophthalmichthys molitrix.  

The areas of Delta and  Río de la Plata suffer the influence of the major urbane 
conglomerates of Argentina, such as the cities of Rosario (Santa Fe province) and 
Buenos Aires. One of the most affected areas is the so-called “Rosario-Magdalena Arc" 
which comprises part of the provinces of Santa Fe and Buenos Aires. In certain areas 
(e.g. Río de la Plata) pollution has led to the disappearance or marked reduction of 
valuable species, such as dorado (Salminus maxillosus), pirapitá (Brycon orbignyanus), 
surubi (Pseudoplatystoma spp.) and pacú (Piaractus mesopotamicus). 

Another noteworthy aspect is the transferral  of waters from the impoundment at 
Yacyretá into Iberá system, with the consequent flooding of fields and wood patches due 
to the rise of the aquifer level (Blanco & Parera, 2001).  
National Protected Areas 
Río Pilcomayo National Park (Formosa). 
Chaco  National Park (Chaco). 
Mburucuyá  National Park (Corrientes). 
Pre-Delta National Park (Entre Ríos). 
Otamendi Strict Natural Reservation (Buenos Aires). 
Colonia Benítez Strict Natural Reservation (Chaco). 
Ramsar sites:  
Río Pilcomayo National Park (Formosa) 
Jaaukanigas river. 
Iberá marshes and lagoons 
Correspondence 
Wetlands:  Región 1,  Región 2 and Región 3 (Cuenca I) . 
Ecoregions: Chaco Húmedo, Esteros del Iberá, Campos y malezales, Delta e Islas del 
Paraná, Espinal (part) and Pampa (part). 
Zoogeography: Subtropical Domain (part of Chacoan and Mesopotamic Districts) and 
part of Pampasic Domain.  
Rationale 

The elements that validate the proposed ecoregion are the following:  
the endemic species mentioned above. ♦ 

♦ 

♦ 

Rivers Paraguay and Paraná, which function as the way of entrance for tropical and 
subtropical aquatic fauna. In addition to  fishes, zooplanctonic elements such as 
some species of rotifers (José de Paggi, 1990) and malacostracan crustaceans 
(Morrone & Lopretto, 1994) may be mentioned. 
the setting established by the alluvial plains of Middle Paraná and Delta, conforming 

9   



 

a series of biotopes that foster  high degrees of biodiversity and  support and shelter 
certain developmental stages of fish populations (e.g. trophic and reproductive 
migrations of Prochilodus lineatus (Bonetto & Castello, 1986; Sverlij et al., 1993; 
Sivansander et al. 2001)). 
The estuary of Río de la Plata acting as a site where complex physical and biological 
phenomena occur, and as  entrance for certain elements of marine origin.  

♦ 

♦ The entire ecoregion is highly dynamic and is influenced primarily by the hydrological 
changes occurring in the upper portion of the main watercourses and by the 
influence of the maritime front on the Río de la Plata estuary. In addition, the 
anthropogenic influence which has promoted, among other consequences, the 
geographical retraction of certain species within Río de la Plata, such as Brycon 
orbignyanus and Ageneiosus valenciennesi, and the entrance, by way of the same 
watercourse, of exotic species such as the Asian bivalves Corbicula fluminea and 
Limnoperma fortunei (Ituarte, 1981; Darrigran & Pastorino, 1985); the latter has 
reached Yacyretá impoundment in Alto Paraná course.  

Relevant Bibliography  
Risso & Morra (1964); Ringuelet (1967); Miquelarena et al. (1980); Cousseau (1985); 
Boschi (1988); Bucher et al. (1993); Baldo et al. (1993/94); Almirón et al. (1992); Menni et 
al. (1992); Quintana et al. (1992); Vega (1995); Liotta et al. (1995/96); Neiff (1996); 
Zalazar (1996); A.A., AGOSBA, ILPLA, SHN (1997); del Barco (1997); Azpelicueta 
(1998); Bonetto & Hurtado (1998); Braga (1998); Mercado et al. (1998); Nion (1998); 
Wells & Daborn (1998); Almirón & Casciotta (1999);  Liotta (1999); Almirón et al. (1992, 
2000); Colombo et al. (2000); Chediak (2000); Remes Lenicov & Colautti (2000); Schnack 
et al. (2000); López et al. (1996); Baigún & Oldani (2001). 

3) LOWER URUGUAY RIVER ECOREGION 
Limits 

To the N, with the Misioneran ecoregion, to the S and W with the Subtropical 
Potamic Axis ecoregion by means of the watershed between Paraná and Uruguay 
rivers, including all the latter’s tributaries in Argentina and, tentatively, the area of Uruguay 
river tributaries in Brazil and Uruguay. 
Description 

This ecoregion includes the areas drained by Uruguay river in Argentinian territory, 
except for the portion belonging to the Misioneran ecoregion.  This basin occupies part 
of the provinces of Corrientes and Entre Ríos. The river arises  in Brazilian territory and 
after  a course of 2,200 km it joins Paraná river to form Río de la Plata.  The basin 
presents a variety of geomorphological features, including numerous valleys and an 
extremely branched (“braided”) fluvial system formed by short steep-sloped watercourses, 
and a series of waterfalls and whitewaters in the main stem, including the waterfall 
situated near Salto city (Uruguay Republic) where Salto Grande dam has been built.  
Downstream from these formations, the river narrows, forming islands and sandbanks; 
just before its mouth, a numerous canals establish communication between Uruguay and 
Paraná rivers. This sector receives strong influences from Río de la Plata river. 
Surface area: approximately  60,230 km2. 
Terrestrial habitats 

The northern portion of this ecoregion has basaltic influences from the Brazilian 
Planalto or Central Plateau, while the southern areas feature sedimentary plains. The 
plant communities comprise vast grasslands with high diversity of grasses such as 
‘flechilla’ (Stipa neesiana), ‘espartillo amargo’ (Elionurus muticus), ‘paja colorada’ 
(Paspalum quadrifarium) and, in some areas, some hard-woodlands formed by ñandubay 
(Prosopis nandubay), algarrobo (Prosopis sp.), molle (Schinus molle) and yatay palm 

10   



 

trees (Butia yatay). 
Aquatic habitats 

In the northern portion of the ecoregion there are lowlands crossed by short rivers, 
while the sedimentary plains in the southern area features slow-drainage watercourses 
with poorly-defined river beds, as well as slough formations draining into Miriñay and 
Aguapey rivers, or  directly into Uruguay river. 
Biodiversity 
Uruguay river: 133 species (30.2%)  
Occurring families: Table 2 

This ecoregion has high ichthyofaunistic affinities with Paraná river (Sverlij et al., 1998), 
albeit with less fish species (30.2%) and  absence of certain families such as 
Lepidosirenidae, Gasteropelecidae, Hypopomidae and Belonidae (Table 2). The only 
recorded endemism is Loricariichthys edentatus. 
Ichthyofaunistic remarks 

The fish assemblage present in this area has suffered the impact of Salto Grande 
impoundment. There have been detectable changes in the fish communities related to  
the environmental modifications brought about by the building of the dam. Among these, 
some remarkable phenomena have been:  an increase in the abundance of 
planktophagous species characteristic of free-flowing waters (e.g. Parapimelodus 
valenciennis and Lycengraulis simulator), while some sedentary species such as Hoplias 
malabaricus have undergone marked regression; differential incidence on migratory 
species, since the populations of some species (e.g. Prochilodus lineatus and Salminus 
maxillosus)  have shown some recovery after initial decrease, but others (e.g. 
Pseudoplatystoma or Sorubim lima) still show declining tendencies. Some species, such 
as Piaractus mesopotamicus and  Brycon orbignyanus, have not been captured since the 
closing of the dam; in this case, these frugivorous species have suffered the 
consequences of the deforestation of the river margins.  

In the lower sector of Uruguay river, the significant biomass of the populations of  
P.lineatus, exploited for industrial uses (elaboration of flour and oils) as well as for direct 
consumption,  supports important commercial fisheries.  
Vulnerable species: species used as live bait (Synbranchus marmoratus  and species of 
Cheirodon and Astyanax), ornamental species such as the Rivulidae (aquarism) 
mentioned above (for Potamic Subtropical Axis ecoregion). 
Biological Value 

This ecoregion includes areas of outstanding biodiversity and protected areas 
representative of the Pampas grasslands (‘Pastizal Pampeano’). Presence of endangered 
species of mammals such as the marshes deer (Blastoceros dichotomus). 
Impacts/Threats 

Advance of agropecuary activities, modification of watercourses (hydraulic works, 
impoundments), habitat fragmentation, inadequate management, destruction of the 
vegetation of the basin, mining activities, presence of urban conglomerates, unregulated 
tourism/recreational activities, poaching, overexploitation of resources. Presence of exotic 
species: Acipenser cf. baeri, Cyprinus carpio and the Asian bivalve Corbicula flaminea 
which has become an important element in trophic webs.  
National Protected Areas 
El Palmar National Park (Entre Ríos province) 
Ramsar Sites 
None. 

11   



 

Correspondence 
Wetlands: Region 1. 
Ecoregions: Campos y Malezales, Espinal, and Pampa. 
Zoogeography: Subtropical Domain, Pampean Province. 

Rationale:  
The elements that validate the proposed ecoregion are the following:  

• The physical and hydrologic characteristics of Uruguay river, which support a 
Paranoplatensean ichthyofauna that is apparently less diverse than the one in Paraná 
river. 

• The river functions as a way of entrance for tropical-subtropical aquatic fauna, such as 
malacostracan crustaceans (Morrone & Lopretto, 1994). 

• The river, whose upper course is winding and irregular, becomes a more typical plain 
river approximately from the level of Santo Tomé town. Its main stem becomes wider 
(1,200 m at Paso de los Libres, Corrientes province) and its elevation decreases, 
providing a favorable habitat for the development of important populations of  ‘sábalo’ 
(Prochilodus lineatus). The river also supports populations of other migratory species. 

Relevant Bibliography 
Di Persia & Neiff (1986); Spinetti et al. (1992); Bonetto (1994); Espinach Ros & Ríos 
Parodi (1997); Sverlij et al. (1998); Chediak (2000); Reis & Pereira (2000); Oldani et al. 
(2001). 

4) EASTERN PARANOPLATENSEAN ECOREGION 
Limits 

To the N, this ecoregion abuts with Paraguay and Bolivia; we have tentatively included 
neighboring areas drained by Paraguay river system in the ecoregion. To the W with 
Western Paranoplatensean and Central Endorrheic ecoregions. To the S, with the 
northern portion of Western Paranoplatensean ecoregion and Salado-Vallimanca 
ecoregion, approximately following the watershed for Salado river in Buenos Aires 
province; to the E, with Subtropical Potamic Axis ecoregion. 

Description 
Situated approximately  between 61ºW and 65º W, an area comprising the upper  (for 

Argentina) courses of allochthonous rivers such as Pilcomayo and Bermejo, and other 
watercourses such as Salado del Norte or Juramento, San Francisco and part of Grande 
de Jujuy rivers.  
Surface area: approximately 417.200 km2.  
Main basins: part of the middle course of Pilcomayo river, Bermejo river (except for its 
lower course), and the above mentioned watercourses. 

Terrestrial Habitats 
This ecoregion combines elements of ‘yungas’ – the cloud forest irregularly  distributed 

in the provinces of Salta, Jujuy, Tucumán and Catamarca – with vast plains, with slight 
eastward slope, occupied by sedimentary deposits of the large Chacoan-Pampean 
tectonic hollow.  

The vegetation, according to the different zones, includes trees such as white ‘tipa’ 
(Tipuana tipu), ‘timbó’ (Enterolobium contortisiliquum), ‘lapacho rosado’ (Tabebuia 
avellanedae), ‘nogal’ (Juglans australis), xerophilous woods with ‘espinillos’ (Acacia 
caven),  ‘horco-quebracho’ (Schinopsis haenkeana), savannahs and grasslands. 

12   



 

Aquatic Habitats  
The ecoregion includes the major part of the course of Pilcomayo river in Argentina, 

Bermejo river, San Francisco, Salado del Norte or Juramento river, and in its southern 
portion rivers Tercero, Cuarto and Carcarañá. Except for Pilcomayo river, which merges 
with Paraguay river, the resto of these watercourses flow into Paraná river along different 
parts of it. Additionally, there are diverse wetlands arising from the hydrologic complexity 
of the area.  

Biodiversity 
Pasaje - Juramento – Salado system:  42 species (9,85%). 
Tercero - Cuarto – Carcarañá system:  37 species (8,4 %). 
Itiyuro or Caraparí river: 2 species (0,5 %). 
Pilcomayo river: 75 species (17,0 %) 
Bermejo river: 116 species (26,3 %) 
Occurring families: Table 2. 

Although the number of species in this ecoregion is important, it’s lower than the values 
for Subtropical Potamic Axis ecoregion. 

There are three endemisms which also occur in Central Endorrheic ecoregion: 
Hypostomus cordovae, Loricaria tucumanensis and Trichomycterus tenuis; and two 
exclusive species: Rhamdella aymarae and Jenynsia maculata. 

Ichthyofaunistic remarks 
Within the province of Formosa there is a reduction in species richness in E-W 

direction (79 species vs. 41, with 31 shared species). Some families are absent: 
Gymnotidae, Hemiodidae, Crenuchidae, Trichomycteridae, Lebiasinidae and 
Aspredinidae (Menni et al., 1992).  Two of the factors that contribute to this reduction are 
the already discussed E-W impoverishment and the decrease of aquatic vegetation, 
correlated to the arid conditions in the area, which reduces the availability of niches for 
certain species. 

The endorrheic Itiyuro river basin, located in Salta province (22° 07’S, 63° 11’W),   500 
m above sea level,  has only two  species recorded; one of them the endemic Rhamdella 
aymarae (Miquelarena & Menni, 1999).   

  In the province of Jujuy there is a thermal water course inhabited by a singular 
species assemblage with ethological particularities. This group is formed by 16 species 
occurring in a high temperature-high salinity habitat, of which 19 are Characiformes, 4 are 
Siluriformes and 2 are Perciformes (Menni et al., 1998). 
Vulnerable species: Loricaria tucumanensis and some species of Cyprinodontiformes, as 
well as the species which are subject to the hydrologic variability of aquatic habitats in this 
area. 

Biological value 
It’s part of an ample semi-arid plain that occupies over 1,200,000 km2 in South America 

and 800,000 km2 in Argentina (the rest being distributed in Bolivia and Paraguay). The 
vegetation is dominated by subtropical thorny woods and semi-arid and humid savannahs, 
with significant species richness especially in the southern sector. Despite the aridity of 
some habitats, there are numerous wetlands of diverse origins, with a variety of  physical 
and biological features. Some areas shelter diverse and abundant avian populations, 
providing breeding areas (for resident species) as well as wintering areas (for Patagonian 
and Pampean species). 

13   



 

Impacts/Threats 
Alteration of water courses, dams and hydraulic centrals, habitat fragmentation, 

poaching, resource overexploitation, inadequate management and destruction of 
vegetation of the basin, unregulated tourism/recreation, as well as  the existence of 
urbane concentrations, industrial activities, mining and oil extraction activities. Presence of 
exotic species such as Cyprinus carpio, Oncorhynchus mykiss, and Gambusia affinis.  

National Protected Areas 
Baritú National Park (Salta province) 
Calilegua National Park (Jujuy province) 
El Rey National Park (Salta province) 
Los Cardones National Park (Salta province) 
Formosa National Park (Formosa province) 
Copo National Park (Santiago del Estero province) 

Ramsar sites 
None 

Correspondences 
Wetlands: Region 2 
Ecoregions: Chaco Seco, Selva de las Yungas, Espinal and Pampa 
Zoogeography: Subtropical Domain, Pampasic Domain, Andean Domain, Central or 
Subandean Domain. 

Rationale:  
The elements that validate the proposed ecoregion are the following:  

• The heterogeneous aquatic habitats that support diverse ichthyofaunistic 
associations. 

• Absence of certain families, such as Clupeidae, Pristigasteridae, Engraulidae, 
Belonidae, Sciaenidae, which are present in Subtropical Potamic Axis 
ecoregion. 

• Decrease in species number when compared to Subtropical Potamic Axis 
ecoregion, directly correlated with the smaller surface area occupied by basins 
in this ecoregion. 

• Presence of thermal watercourses with species adapted to high temperature 
and salinity conditions.  

Relevant Bibliography 
Casciotta et al. (1989); Menni et al. (1992); Haro & Bistoni (1996); Bucher & Chani (1998); 
Haro et al. (1998); Menni et al. (1998). 

5) CENTRAL ENDORRHEIC ECOREGION 
Limits 

To the N, the northern watershed of Tala river basin and San Esteban hills (Salta 
province).  

To the E, the boundary with Pasaje-Juramento-Salado system (Salado river basin) 
marked by the mountain ranges of Sierras de la Candelaria and the riverbeds of Muerto, 
Mista and Los Gómez watercourses. See further comments in the description of the basin.  

To the W, a series of sierras (Carahuasi, Aconquija, de la Carreta, Humaya, Las 
Higueritas and del Potrerillo), the hills  that mark the Huacra or San Francisco river basin 

14   



 

towards Catamarca province and the dry bed of this stream, and the valley enclosed 
between Sierras Grandes and Comechingones in the west, and Ancasti sierras in the 
east. 

To the S, an imaginary line following the boundaries of Segundo river basin (about 31° 
50’S) and extends from Cerro Negro (Comechingones sierras system) through the towns 
of Monte Ralo, Oncativo and Devoto, reaching Mar Chiquita lagoon.  

Description 
This ecoregion comprises almost all of the territory of Tucumán province, the western 

and southern sectors of Santiago del Estero province and the northwest of Córdoba 
province. The landscape is subject to rapid transformation due to erosive and sedimentary 
processes, accelerated mainly by the poor management of soils and vegetated areas. The 
area undergoes significant periodic floods that affect vast areas. Another frequent 
phenomenon is the transferral of waters from Dulce river to Salado del Norte river, when 
the river flows over the drainage divide. There are numerous small and middle sized 
endorrheic water courses that become salt pans (‘salinas’) during the dry season.  
Surface area: about 149,800 km2.  
Main basins: Salí-Dulce  river system (Salí river changes its name to Dulce after Río 
Hondo impoundment), Mar Chiquita (‘Ansenuza Sea’) basin with rivers Primero and 
Segundo, and various rivers and lesser streams situated in the northwestern region of 
Córdoba province.  

The main dams are El Cadillal (Tucumán province) on the Salí river course, and Río 
Hondo,  situated in the provinces of  Tucumán and Santiago del Estero, between 27º 27’ 
S and 27º 39’ S, and 64º 52’ W and 65º 05’ W. 

Terrestrial Habitats 
The dominating plant communities are the xerophyle woods,  included in the Chaco 

Seco biome. There are also abundant Sierran woods, savannahs and grasslands. In the 
higher  flat areas communities such as xerophyle ‘quebracho’ woods (species of 
Aspidosperma and Schinopsis), thorny shrubs, etc. In some of the lower areas, where the 
salinity conditions and the restricted drainage affect the floristic assemblage, communities 
of ‘algarrobo’ (Prosopis spp.) and ‘chañar’ (Geoffroea decorticans) occur, and halophyte 
plants grow in the  areas of salt plains. There are alternating forest and grassland 
formations, the latter associated with filled-in riverbeds. In the sierras portion of Chaco, 
palm-tree associations including ‘carandilla’ (Trithrinax campestris) also occur. 

There are fragmentary patches of ‘Yungas’ (cloud forest) formations in Tucumán 
province,  generally associated with the subandean sierras. 

Aquatic Habitats 
♦ Salí-Dulce river: its active basin is situated in the provinces of Tucumán, Salta and 

Catamarca. Most of its main tributaries descend from the Aconquija and Calchaquí 
sierras formations. Salí river is formed in the junction of Tala and Candelaria rivers 
(each with several tributaries). When the river exits Río Hondo impoundment it 
receives the name of Dulce river and flows over flatlands, receiving almost no 
tributaries and flowing finally into Mar Chiquita lagoon. The basin presents  
considerable altitudinal variation, ranging from 270 m above sea level at Río Hondo 
impoundment to 70 m above sea level at Mar Chiquita lagoon.  

♦ Primero (Suquía) river: it’s surrounded by areas of considerable urban 
concentrations. Its upper course receives two main tributaries: Cosquín river with its 
own tributaries (San Francisco river and various creeks and rivulets) and San Roque 
river with tributaries Chorrillos river, San Antonio creek, etc.; the latter flows into the 
artificial lake in San Roque dam.  

15   



 

♦ Segundo (Xanaes) river: the basin boundary extends from Pampa de Achala, 
through the towns of Alta Gracia, Río Segundo and Cañada de Machado to Mar 
Chiquita lagoon; to the S, an imaginary line from Cerro Negro (Comechingones hills 
system)  through Monte Ralo, Oncativo, Devoto, to Mar Chiquita lagoon. 
Hydrographically the basin has three areas: 
a) Zone of sierras, on the N, S and W zones of the basin, with a surface area of 

approximately 2,000 km2, including the two main feeding water courses, rivers De 
los Molinos(with its tributaries San Pedro river and various creeks, that contribute 
their waters to the impoundment in Los Molinos dam) and Anizacate (with its 
tributaries de la Suela and San José rivers).  

b)  Zone of plains, from the headwaters of Segundo river itself to Villa del Rosario 
(Córdoba province), surface area about 4,000 km2. 

c) Zone of marshes: marshes formed by the main stem and also by other brooks and 
creeks that run parallel to Segundo river, with a surface area of 6,700 km2.  

♦ Mar Chiquita "Laguna" (lake) (Sea of Ansenuza): situated in the low saline grounds 
in the NE of Córdoba province, between 26°-32° S and 62°-66°W, along with the 
saline Los Porongos lagoons. Mar Chiquita has a surface area  that fluctuates 
between 2,000 y  6,000 km², being 140 km long and 100 km wide. It’s one of the 
world’s largest saline lakes; it’s far from populated areas. Its main features are its 
shallow depths and  brackish  waters, with salinity values ranging from 40 to 250 g/l, 
according to the water level in the lagoon. This water body is particularly subject to 
flood-drought cycles produced by summer rains that fall upstream in the basin. A 
conspicuous rise  in the water level of this lagoon started in 1970 and continues to this 
day; simultaneously, the waters contributed by the tributary streams have determined 
a marked decrease in the saline concentration that has fostered the advance of the 
silverside Odontesthes bonariensis, introduced in the area.   

♦ Rivers of the NW of Córdoba province: this basin comprises the rivers, creeks and 
rivulets that descend from the western slopes of the Córdoba sierras. To the N, its limit 
is a line extending from El Tuscal (Salinas Grandes), through La Esperanza to San 
Francisco de Chañar; to the W, a line that borders Salinas Grandes, El Tuscal, San 
José, San Antonio, Serrezuela and the southernmost tip of the salt flats to the south, 
through Pinas, Los Cerrillos, to Piedra Blanca creek (in the San Luis-Córdoba border); 
to the S, through Piedra Blanca creek to the heights of Comechingones sierras; to the 
E, from San Francisco del Chañar passing through various hills to La Cumbre, then 
from Sierra Chica to Sierra Grande, Pampa de San Luis and Pampa de Achala to 
Piedra Blanca creek. 

This basin comprises two sectors:  
a) Salinas Grandes slope, including the rivers of the northern area (western slope) 

that flow toward the Salinas Grandes salt plains. Most of these water courses are 
only connected to the salt plains during the rainy season; the rest of the year, their 
courses fade into marshes or are absorbed by sand expanses ('arenales'). Cruz 
del Eje river, with its tributaries Pintos, Avalos and de la Candelaria rivers, is one 
of the main water courses, with a basin surface area of approximately 1,700 km2. 
Other important rivers are Pichanas, de Soto, Los Sauces and Guasapampa.  

b) Western sector: the water courses descend from the western slope of the central 
mountain range. The only important river is San Pedro or de los Sauces, formed 
by the intersection of Mina Clavero and Panaholma rivers. Other water courses 
are Chancarí river and various creeks.  

Biodiversity  
Salí-Dulce river: 64 species (14.5 %). 
Primero river: 21 species (4.8 %). 

16   



 

Segundo river: 20 species (4.5 %). 
NW Córdoba water courses: 11 species (2.5 %). 
Occurring families: Table 2. 

There are endemic species in Primero and Segundo basins (e.g. Bryconamericus 
eigenmanni and Astyanax cordovae) as well as some species of Loricariidae and 
Trichomycteridae that are unique to Argentina (e.g. Hypostomus cordovae and 
Trichomycterus tenuis). Another endemic species is Loricaria tucumanensis (an 
endemism also present  in some areas of Jujuy province  included in Eatern 
Paranoplatensean ecoregion) (Menni et al., 1998). Trichomycterus alterus and Jenynsia 
pygogramma are endemic species shared with Subandean-Cuyan and Western 
Paranoplatensean ecoregions. (Table 6). 

Ichthyofaunistic remarks 
The pauperization of the paranoplatensean ichthyofauna is evinced in the main 

hydrogegraphical axis of the ecoregion, the Salí-Dulce river (Table 4). Throughout this 
basin some orders, such as Myliobatiformes, Clupeiformes, Lepidosireniformes, 
Beloniformes and Pleuronectiformes, are absent (Table 2); the absence of 
Trichomycteridae in Dulce river is a particular feature. 
Vulnerable species:   Trichomycterus corduvensis (Miatello, 1994), Loricaria 
tucumanensis (Vides-Almonacid et al., 1998). 

Biological value 
The system includes some 'areas of outstanding diversity' of Chaco Seco and Chaco 

Serrano (Bertonatti & Corcuera, 2000). 
The sector of  Pampa de Achala (Córdoba province) has a significant number of 

endemisms; e.g. Achala toads (Bufo achalensis and Pleurodema kriegii), Achala 
‘escuercito’ toad (Odontophynus achalensis), and the Achala green lizard (Pristidactylus 
achalensis), as well as endemic subspecies of birds and mammals, and one endemic 
invertebrate (the scorpion Urophonius achalensis). 

Impacts/Threats 
Urban concentrations; hydraulic works; agropecuary activities; mining activities; various 

industries. Introduced fish species: Cyprinus carpio, Gambusia affinis, Oncorhynchus 
mykiss, Carassius auratus. 

National Protected Areas 
Campo de los Alisos National Park (Tucumán). 
Quebrada del Condorito National Park (Córdoba). 

Ramsar Sites 
None. 

Correspondence 
Wetlands: Region 2. 
Ecoregions: Chaco Seco, Espinal. 
Zoogeography: Subtropical Domain (Chacoan District) and Pampasic Domain. 

Rationale 
The elements that validate the proposed ecoregion are the following:  

♦ An important reduction in the number of species relative to those that occur in 
Subtropical Potamic Axis ecoregion, that is correlated with the already discussed 

17   



 

general pauperization in east-west direction (Table 4). This is evinced here by the 
absence of some orders and families (Table 2) that may have inhabited the area in 
former times, as demonstrated by fossil records of Cynodontidae and Scienidae from 
Middle Miocene in Salta province (Cione & Casciotta, 1995). 

♦ The presence of endemic species in Salí, Primero and Segundo river basins.  
♦ The NW region of Córdoba province might represent an ecotonal area between the 

Paranoplatensean and Subandean-Cuyan provinces (Menni et al., 1984).  

Relevant Bibliography 
Bonetto et al. (1976); Casciotta et al. (1989); Miquelarena et al. (1990); Buti & 
Miquelarena (1995); López et al. (1996); Miquelarena & Aquino (1995); Haro & Bistoni 
(1996); Reati et al. (1997); Bucher & Chani (1998); Cabido (1998); Fernández (1998); Buti 
& Cancino (1999); Miquelarena & Aquino (1999); Anónimo (2000); Kutel & Bistoni (2000). 

6) WESTERN PARANOPLATENSEAN ECOREGION 
Limits 

This ecoregion includes two sectors.  
Septentrional Sector: The limits for the  Northern sector are: to the N, the political border 
in Salta province, from 22º 08’ S. To the W, the mountain range of the Andes from 
22º08’S and 68º36’W; although we have extended tentatively these limits to include some 
neighboring basins in Bolivia.  To the E, from 65º11’W the area is bound by Pilcomayo 
river basin (included) and part of Bermejo river basin, the watershed separating Pasaje-
Juramento-Salado basin (which is included in the Eastern Paranoplatensean 
ecoregion) and Central Endorrheic ecoregion (see description for Salí-Dulce basin). To 
the S, the limits between Abaucán river basin (included in the ecoregion) and Vinchina or 
Bermejo basin (this river is a tributary of Desaguadero river and is included in the 
Subandean-Cuyan ecoregion); this division between the watersheds coincides in the 
western portion with the political Catamarca-La Rioja border, and partially with the heights 
of Famatina orographic system. This limit continues in the Paiman sierra that separates 
the Blanco and Achavil river basins, to the E by watercourses such as Anguil river and 
other tributaries of Los Sauces river (that descend from Velazco hills), and then turns 
south including the marshes where Salado river disappears (Desagües del Salado). 
These marshlands are situated south of Ambato hill, in La Rioja province (approximately 
at 66º30’W). 
Meridional Sector: to the N the limit is over the 32ºS parallel between 64º50’W and 
66º55’W. To the W, the 66º55’ meridian between 32º and 33º40’ S, and south of 
approximately 33º30’ this limit reaches the 64ºW meridian to include Quinto river basin in 
San Luis and Córdoba provinces. To the S, following the watershed of Quinto river, as a 
diagonal line extending from approximately 34º S and 66º30’W to 34º30’S and 63º40’W. 
To the  E, the meridional sector abuts with Eastern Paranoplatensean and Salado del 
Sur-Vallimanca ecoregions. 

Description 
The ecoregion encompasses varied landscapes: a prolongation of the Bolivian 

Altiplano, with mountain ranges including several volcanoes; an arid region with varied 
geological, geomorphological and altimetric features associated with the cordilleran 
system and the subandean hills; and also a sector with dense forest cover. Heights vary 
between 400 and 4,500 m.; there are valleys, elongated in north-south direction, ample 
slopes, and little-sloped plains derived from intermountain valleys. 
Surface area: approximately 248,760 km2. 
Main basins: rivers Quinto, Conlara, Chorrillos; the rivers descending from the western 
and northern slopes of San Luis sierras: rivers Nogolí, Amieva, San Francisco, San 

18   



 

Martín, Cautana, etc.; the lagoons in southern San Luis province.  
In addition to the mentioned watercourses, there are streams with headwaters located 

in the mountains of Andean and Subandean orographic systems.  

Terrestrial Habitats 
Different plant associations according to the altitudinal gradient: shrubby steppe, open 

woods with low trees such as ‘queñoa’ (Polylepis tomentella), and shrubs as ‘jarillas’ 
(Larrea sp.), ‘retamo’ (Bulnesia retama), ‘pichana’ (Psila spartioides), tall cactuses or 
‘cardones’ (Trichocereus sp.), halophytic communities (rushes),  other trees such as 
‘algarrobos’ (Prosopis sp.), and cloud forest species such as white ‘tipa’  (Tipuana tipu) 
and laurel (Phoebe sp.). 

Aquatic Habitats 
This ecoregion features diverse high-elevation wetlands (saltpans and lagoons), 

temporary endorrheic or  poorly drained basins, and some permanent watercourses 
associated with the gradual thawing of mountain snow. 

The Meridional sector includes all the endorrheic watercourses that flow down from the 
San Luis hill system and the western slopes of Comechingones sierras, in San Luis 
province, as web as tose from the eastern slope of Alto Pencoso hills.  

Quinto river basin, with a surface area of approximately 1,800 km2, is the main 
watercouse in San Luis province. Some of its tributaries are Grande and De la Cañada 
Honda rivers;  further on downstream it receives Saladillo stream, whose main 
contribution is subterranean. Quinto river disappears forming the sloughs called ‘Bañados 
de La Amarga’, situated in southern Córdoba province. 

This ecoregion also includes the ‘Salinas del Bebedero’ saltpans, which used to be 
connected with Desaguadero river basin (Central Endorrheic ecorregion), and  an area in 
southern Córdoba province which undergoes sporadic floods due to the swelling of Quinto 
river, although  these phenomena are at present attenuated by La Florida dam built in 
Quinto river.  

Biodiversity 
Tributaries to Pipanaco saltflats: :  11 species (2,5  %). 
Del Valle and  Dorado rivers:  3 species (0,7 %). 
Abaucán, Colorado or Salado river:  3 species (0,7 %). 
Del Valle (other) river and watercourses from eastern slope of Ambato hills (Catamarca 
province):  3 species (0,7 %). 
Rivers and streams of the Puna region:  1 specie (0,2 %). 
Quinto river: 5 species (1,1 %) 
Chorrillos river: 2 species (0,5 %) 
Occurring families: Table 2. 

The endemic species are Rineloricaria catamarcensis, Trichomycterus catamarcensis 
and T. ramosus; other endemic species, T. roigi, T. alterus and Jenynsia pygogramma 
also occur in Central Endorrheic and Subandean-Cuyan ecoregions (Table 6).  

Ichthyofaunistic remarks 
The occurrence of fish species is associated with the altitudinal range of this ecoregion; 

there  are  endemisms, largely among the Trichomycteridae. 
This ecoregion comprises two sectors which form an ichthyofaunistic unit, although 

they are apart from a geographical point of view. Their similitudes include families in 
common, such as Trichomycteridae, Characidae y Pimelodidae; and similar  biomes. 

19   



 

Biological value 
This ecoregion comprises ‘areas of outstanding biodiversity’ of diverse biomes: 

‘Yungas’, ‘Monte’, ‘Puna’, ‘Prepuna’ and ‘Andes Áridos’. 

Impacts/Threats 
Mining and agropecuary activities; hydraulic works, construction and laying of gas 

ducts. 

National Protected Areas 
Laguna de los Pozuelos Natural Monument (Jujuy province) 

Ramsar Sites 
Laguna de los Pozuelos Natural Monument (Jujuy province) 
Vilama lagoons (Jujuy) 

Correspondence 
Wetlands: Regions 6 and 2 (in part) 
Ecoregions: Altos Andes, Puna, Monte de Sierras y Bolsones, Selva de las Yungas. 
Zoogeography: Subtropical Domain, Andean Domain, Central  or Subandean Domain. 

Rationale 
The elements that validate the proposed ecoregion are the following:  

♦ This area marks the western distributional limit of Paranoplatensean ichthyofauna, 
with species of Characidae and Loricariidae. 

♦ Occurrence of endemic species of Trichomycteridae and Anablepidae, also shared 
with Subandean-Cuyan and Central Endorrheic. 

♦ Presence of endemic species of Trichomycteridae associated with altitudinal 
variations. 

Relevant Bibliography 
Boulenger (1902);Marini et al. (1933); Arratia & Menu Marque (1984); Bucher & Chani 
(1998); Sarmiento et al. (1998); Fernández (2000); Fernández & Vari (2000). 

 
7) SALADO DEL SUR-VALLIMANCA ECOREGION 

Limits 
To the SE the ecoregion reaches Samborombón bay (coastal Buenos Aires); to the NE 

it borders the Subtropical Potamic Axis ecoregion; to the NW, it abuts on the Eastern 
Paranoplatensean Ecoregion; to the W, on La Pampa province (no-records area) 
excepting a narrow eastern area included  within this ecoregion); to the SE, on the 
Bonaerensean Atlantic Drainage ecoregion.  
Description 

This ecoregion is situated  in the sector of flat ‘pampas’ (plains), and comprises a wide 
central area in Buenos Aires province, from Samborombón bay in the E to La Pampa 
province in the west, including numerous and varied aquatic environments. The lagoons 
have two types of cross-sectional profile: some of them, with more regular borders and 
generally smaller and less stable, have pfanne- or plate-shaped beds; other lagoons, 
which are larger and more stable, generally with more irregular borders and also 
interconnected (chained lagoon system or “encadenadas”), have more of a tub- or barrel-
shaped cross-sectional profile. The NW arid area is the most arid part of the ecoregions; 
the hydrographic network has no drainage and undergoes alternating wet and dry periods 

20   



 

determined mainly by the precipitation/evaporation ratios. The lotic habitats are flatlands 
streams, which are generally temporary, and man-made drainage canals. 
Surface area: about 179,000 km2. 
Main basins: two large rivers, Samborombón and Salado del Sur, with their tributaries. 
Other water courses are Vallimanca stream and the endorrheic basins situated in the NW 
and SW of the ecoregion. 

Terrestrial Habitats 
This ecoregion features horizontal or slightly ondulated plains, with some low hills (up 

to 1,200 m) emerging as islands in the flat landscape. The dominant plant community is 
the graminaceous steppe or pseudosteppe, and there are also prairies, psammophyte and 
halophyte steppes (with species such as Salicornia ambigua and Chenopodium 
macrospermum), riparian forests and diverse types of hydrophytes (e.g. rushes: 
Schoenoplectus californicus and S. americanus). This landscape has undergone 
important modifications due to the influence of human activities, especially the advance of 
the agropecuary activities. 

Aquatic Habitats 
♦ Salado del Sur river: this river is the southernmost tributary of Río de la Plata; it runs 

over plains and its bottom is flat and covered by siltation processes.  The river forms 
several marginal lagoons and develops numerous winding meanders along an ample 
and almost flat valley. Its basin is Y-shaped, with two main branches; one of them 
arises in a series of lagoons situated in the SE of Santa Fe province; the other, in 
Departamento de Saladillo (Buenos Aires province). The river is about 690 km long 
and it flows finally into the sea at Samborombón bay. In addition to its surface 
tributaries, it also receives water from underground sources.  

♦ Samborombón river: this is also a flatlands stream, with low margins and a shallow  
valley; it runs for some 150 km and reaches Samborombón bay, where it flows into the 
Atlantic Ocean.  

♦ Vallimanca creek: the main tributary of the Salado del Sur river. Its headwaters are in 
the southern part of Partido de Bolívar (Buenos Aires province), it runs following the 
boundary of the basin and finally flows into Salado del Sur river through a man-made 
canal (Canal 16). 

♦ Lentic habitats: within the valley of Salado river there are 339 lagoons of variable 
salinity, of which 125 are temporary. The Encadenadas (chained lagoons) of 
Chascomús have been fairly researched; this lacustrine system comprises, among 
others, the ‘lagunas’ (permanent ponds) Vitel (13 km2), Chascomús (30 km2), Adela or 
Manantiales (21 km2),  del Burro (11 km2), Tablillas (17 km2), Chis Chis (15 km2) and 
Las Barrancas (9 km2), all of them interconnected via short water courses and  flowing 
finally into Salado river by way of the last mentioned lagoon. They are part of the 
Northern and Marginal Group of  Frenguelli (1956). 
In the SW sector there are 61 lagoons (37 of them temporary), and the main ones form 
the Encadenadas del Oeste system (Alsina, Cochicó, del Monte, del Venado and 
Epecuén), with a surface area of nearly 580 km2.  One of their main features is the 
marked salinization gradient that increases westwards (López et al., in press). These 
lagoons are part of the Diagonal  Group of Frenguelli (1956). 

Biodiversity 
Salado del Sur river:  43 species (9.8 %). 
NW Pampean basins: 3 species (0.7%) 
SW Pampean basins: 17 species (3,9 %) 
Occurring families: Table 2. 

21   



 

There is one exclusive endemic species, Austrolebias nonoiuliensis, and another 
endemic species, Megalebias elongatus, which also occurs within the Subtropical 
Potamic axis ecoregion (Table 6). 

One of Argentina’s emblematic species, the silverside ('pejerrey') Odontesthes 
bonariensis, exhibits high productivity within the Salado basin.  

In the NW sector of the ecoregion, occurrences of fishes are almost non-existent, with 
the exceptions of the records for Odontesthes bonariensis, Cyprinus carpio and Rhamdia 
quelen in El Hinojo lagoon (López et al., 1991) and Jenynsia sp. (D. Colautti, pers. 
comm.). 

Ichthyofaunistic remarks 
The Salado river basin marks the southern limit for the distributional range of most of 

the paranoplatensean species. We may add to the reasons commented by other authors 
(Ringuelet, 1975; Menni & Gómez, 1995; Gómez, 1996) the  characteristics of the Río de 
la Plata estuarial ecosystem, especially at its external zone, where the waters are 
brackish and the salinity is variable (Boschi, 1988).  

The decrease in species richness becomes apparent in general NE-SW direction. The 
effect of the barriers, mainly ecological in nature, is indicated in the absence of at least 
three orders and eleven families which are frequent in the Río de la Plata basin (Table 2). 
Within the occurring species, Characiforms are dominant over Siluriforms by 38 % (López 
et al., 2001). 

The presence of one of the emblematic species of Argentina, the “pejerrey” (freshwater 
silverside), that has been the object of much research and diverse literature (Ringuelet, 
1943; López et al., 1991; Grosman, 1995, 2001) is worthy of mentioning. 

The species of the genera Austrolebias and Megalebias represent a group with 
remarkable reproductive features, adapted to temporary water bodies that become dry 
and dissapear in summer.   

The mullet (Mugil liza), whose biology in this area is poorly known, is the only 
amphibiotic species (Table 7).  

A significant phenomenon is directly related to the swellings of the main rivers that form 
the Río de la Plata system, especially Paraná river. These events produce an expanded 
flow of fresh water into Samborombón bay, and allow the entrance to Salado river  of 
some species that are frequently mentioned as occasional for the basin. Among these we 
may mention Brevoortia pectinata, Prochilodus lineatus, Acestrorhynchus pantaneiro, 
Salminus maxillosus, Hyphessobrycon meridionalis, Pygocentrus nattereri, Serrasalmus 
spilopleura, Callichthys callichthys,  Trachelyopterus striatulus, Ageneiosus valenciennesi, 
Luciopimelodus pati, Pimelodus maculatus and Gymnotus carapo.  
Vulnerable species: those species used as bait (genera Cheirodon and Astyanax and 
the swamp eel, Synbranchus marmoratus), and those considered ornamental (aquarism) 
such as the species of Rivulidae already mentioned in the discussion of the Subtropical 
Potamic Axis ecoregion. 

Biological value 
A reduced and fragmented population of Pampa’s deer (Ozotoceros bezoarticus) 

inhabits the area of  'cangrejales'  (crab colonies) in Samborombón bay  (Merino, 1994).  
Salado river acts as a “temporary corridor” for the ichthyofauna, many species  

occurring occasionally within the watercourse.  
The Salado basin and the system of chained lagoons of Chascomús are considered as 

“area of outstanding biodiversity”, as well as the Samborombón bay area.  
The crab colonies in Samborombón bay, the Encadenadas lagoons of Chascomús and 

the Salado del Sur are considered as unique environments by Canevari et al. (1998).  

22   



 

Impacts/Threats 
Agropecuary expansion, watercourse alteration, habitat fragmentation, inadequate 

management, overexploitation of resources and unregulated tourism/recreational 
activities. 

Desertification phenomena are occurring  in the northeastern portion of the Salado 
basin. 

The only exotic species that has become acclimated in the Salado basin is the 
common carp, Cyprinus carpio. As in other areas of Argentina, this species has been 
particularly successful in Buenos Aires province and it’s estimated to occur in over 90 % 
of the freshwater environments of the province (López et al., 1996). Along with the 
silverside, this species forms  the largest ichthyic biomass for this basin and, although 
there has been an increase in  knowledge of its ecology (Colautti, 1997), the effect of this 
species on ecological systems is still being discussed (Grosman, 1995). Apart from this, 
the species Oncorhynchus mykiss has been introduced in some hilly  areas, with variable 
success (Table 3). 

National Protected Areas 
None. 

Ramsar Sites 
Samborombón bay. 

Correspondence 
Wetlands: Region 3, excepting part of Basin I and Basin IV. 
Ecoregions: Pampa. 
Zoogeography: Pampasic Domain. 

Rationale 
The elements that validate the proposed ecoregion are the following:  

♦ It is the southern distributional limit for most of the paranoplatensean species, and 
many orders and families of common occurrence in the Subtropical Potamic Axis 
ecoregion are absent here (Table 2). 

♦ The singular arrangement  of the hydrographical system, consisting of one plains river 
that from its origin is associated with diverse lacustrine systems, achieving a particular 
dynamic flow that is unique in Argentina.  

♦ Another particular feature of the Salado del Sur river is its function as “temporary 
corridor” for certain fish species at times of occurrence of global hydrological events 
such as the extensive floods in the Subtropical Potamic Axis ecoregion. These 
conditions produce changes in physical and chemical factors in the area that could 
explain the occurrence of some of the so-called "occasional" species.  

♦ The presence of the endemisms Austrolebias nonoiuliensis and Megalebias elongatus 
(the latter, as we have mentioned, also occurs in the Subtropical Potamic Axis 
ecoregion.  

Relevant Bibliography 
Toresani et al., (1994); Iriart (1997); Gómez & Toresani (1998); López et al. (1991, 1993, 
2001); Van Eerden & Iedema (1994); Miquelarena & López (1995). 

 
 
 

23   



 

8) BONAERENSEAN ATLANTIC DRAINAGE ECOREGION 
Limits 

To the N, this ecoregion abuts mostly on Salado del Sur-Vallimanca ecoregion (Salado 
river basin), following an imaginary line passing south of Canal 2 (which flows into 
Samborombón Bay), including all watercourses south of it. To the NW, by the watershed 
formed by the Balcarce and Tandil hills, from the Atlantic coast and reaching Tandil city. 
To the E, the basin is closed by the sand dunes which lie along the Atlantic coast, behind 
the beaches. To the W, the limit is an imaginary line in southwestern Buenos Aires 
province, including Sauce Chico river basin and Chasicó lagoon and all its tributary 
watercourses. To the SW, the no-records area separates this area from Patagonian 
ecoregion. 

Description 
This is a region where plains are the prevailing landscape, and two hilly formations 

stand out: septentrionlly Sierras de Tandil, and meridionally Sierra de la Ventana. The 
Tandil hills have metamorphic and sedimentary rocks, it’s approximately 300 km long, 50 
km wide and has an average height of 450 m. Sierra de la Ventana is an outcrop of 
Paleozoic sedimentary rocks, with an average height of 700 m (its maximum height is 
1,239 m). Another outstanding feature is the area where Chasicó lagoon is situated, which 
is several meters under sea level.  
Surface area: approximately 67,880 km2.  
Main basins: this area has scarce hydrographically significant features; there are no 
major watercourses. Some of the rivers are Quequén Grande, Quequén Salado and 
Sauce Grande. 

Terrestrial Habitats  
These are similar to the ones in Salado del Sur-Vallimanca ecoregion; among the 

grasslands, the sand dunes represent true "islands" with scarce vegetation including the 
characteristic ‘Pampa’s grass’ (Cortaderia selloana), and inhabited by typical flora and 
fauna.   

The ‘talares’ (associations of ‘tala’ Celtis tala and other species of bushes and low 
trees) are the only autochthonous arboreal formations in the ‘pampas’, a landscape that 
has undergone significant changes due to anthropogenic activities.  

The coasts of Mar Chiquita coastal lagoon are occupied by salt marshes with clayish 
soils, inhabited by dense crab colonies and other invertebrate fauna.  

Aquatic Habitats 
This ecoregion includes all watercourses descending from the western slope of 

Tandilia and Ventania systems, e.g. rivers such as Sauce Grande,  Chelforó, Napaleofú, 
Quequén Grande, Claromecó,  and Napostá Grande. Some of the rivers flow directly into 
the sea coast, while others reach the ocean indirectly through other streams or man-made 
canals, and yet others disappear in sloughs or lagoons, the development of which is 
fostered by the presence of the coastal sand dunes.   

An outstanding feature is Salada Grande lacunar complex, with a surface area of  
1,350 km2.  

Mar Chiquita coastal lagoon has a surface area of some 5,000 has and its maximum 
depth ranges between 4.9 m and 1.8 m (in low periods). It’s separated from the ocean by 
the surrounding sand dunes and connected to it by a narrow mouth. The oceanic 
influence on the coastal lagoon is variable and depends on several factors. This 
waterbody receives also waters from various streams (such as Las Gallinas, Grande, 
Vivoratá, and Dulce streams). The landscape is markedly dynamic, due to accretion and 
erosion proceses, and changes in the shape of the marine coasts of the area and the 

24   



 

mouth of the  lagoon are relatively swift.  
In a more southerly location, in Monte Hermoso city, Sauce Grande lagoon has a 

surface area of 2,290 ha.  
There is one artificial lentic body in the ecoregion:  Paso de las Piedras dam, built on 

Sauce Grande river. The impoundment has a surface area of 3,300 ha and an average 
depth of 10 m. 

Biodiversity 
Pampean basins of Atlantic drainage:  26 species (5,9 %). 
Occurring families: Table 2. 
There are no endemic species. 

Ichthyofaunistic remarks 
There are 26  species in this area (5.9%) (Table 1). This assemblage comprises widely 

distributed Brasilic species such as Cheirodon interruptus, Astyanax eigenmanniorum, 
Bryconamericus iheringi, Hyphessobrycon anisitsi, Oligosarcus jenynsii (Characiformes);  
Rhamdia quelen, Corydoras paleatus (Siluriformes); “Cichlasoma” facetum (Perciformes) 
and Synbranchus marmoratus (Synbranchiformes); as well as families with marine and 
euryhaline  representatives (e.g. Clupeidae, Mugilidae and Atherinopsidae) (Table 7). The 
presence of the alter is related to breeding activities in the area.   
Vulnerable Species: none. 

Biological Value 
The wetlands in this area give shelter to populations of diverse species and function as 

concentration sites for migratory shorebirds. The crab colonies might be considered of 
international significance according to Ramsar criteria.  

Mar Chiquita coastal lagoon is an estuarial environment with high biological richness 
and diversity, considered as a wildlife shelter of regional importance.   

The marine coastal area is inhabited by  important populations of anchovy (Engraulis 
anchoita) and Plata river dolphin (Pontoporia blainvillei). 

It’s included in the areas of outstanding biodiversity of the Pampean Region. 

Impacts/Threats 
Agriculture, agropecuary expansion, alteration of watercourses, urban expansion, 

habitat fragmentation, inadequate management, resource overexploitation, unregulated 
tourism/recreational activities, energy generation, portuary activity.  

The only exotic species recorded in this ecoregion is the black bass, Huro salmoides, 
which was introduced in Laguna de Los Padres lagoon approximately 40 years ago. 
There are no current records of its presence there.  

National Protected Areas  
None. 

Ramsar sites 
None. 

Correspondence 
Wetlands: Region 3, in part (basins IV and VI). 
Ecoregions: Pampa. 
Zoogeography: Pampasic Domain. 

25   



 

Rationale  
The elements that validate the proposed ecoregion are the following:  

• Absence of endemisms. 
• Presence of euryhaline families, due to the combination of the significant marine coast 

with  the lentic and lotic environments which are associated with it.  
• The existence of Mar Chiquita coastal lagoon, a sheltering and breeding area for 

diverse species.  
• The southern distributional limit of species considered ‘indicators of ichthyological 

regions’, belonging to Characiformes, Siluriformes,  Perciformes and 
Synbranchiformes, is found within this ecoregion.  

Relevant Bibliography 
Dangavs, N. V. (1988); Padín et al. (1991); Gómez & Toresani (1998); Casciotta et al. 
(1999); Cousseau et al. (2001); Iribarne (2001). 

9) SUBANDEAN-CUYAN ECOREGION 
Limits 

To the N, the borders of Western Paranoplatensean ecoregion following diverse 
watersheds (see description of that ecoregion). To the S, with the NW sector of 
Patagonian ecoregion. To the W, the watershed formed by the Andes mountain range.  
To the E, with the SW sector of Central Endorrheic ecoregion, with part of San Luis 
province, included in the meridional sector of Western Paranoplatensean ecoregion, 
and with the no-records area.  
Description 

This ecoregion comprises all of the province San Juan, most of the provinces of  La 
Rioja and Mendoza, the NW  of La Pampa and two narrow elongated areas in the western 
and northern peripheral areas of San Luis.  

López (2001) states that Mazza (1961) in his hydrological classification included this 
ecoregion between the areas of  Interior Rivers without oceanic drainage and Atlantic 
drainage rivers. Bonnetto (1994) situates this area within his Region III, that he 
designated as Atlantic drainage rivers of Patagonic-Chilean Subregion. Marzo and 
Arias (1975) included this fluvial system within Rivers of the Andean hydrographical 
system, situated in the so-called ‘Arid diagonal’ in South America. This group of rivers 
have been called indistinctly Andean or ‘Desaguadero’ system; its main tributaries are 
rivers Jáchal, San Juan, Mendoza, Tunuyán, Diamante and Atuel. The collector river for 
these streams flows through an area of dry courses, sloughs and lagoons, and finally into 
the upper course of Colorado river.  

There is also the lacustrine complex  of Guanacache lagoons, situated in the border 
between the provinces of San Juan, Mendoza and San Luis.  

The saline Llancanello lagoon (650 km2) lies south of the city of San Rafael (Mendoza); 
it receives waters from Mendoza river, Mocho and Chacay creeks and  also significant 
contributions from  phreatic waters (Iglesias & Pérez, 1998).  
Surface area: 365,000 km2. 

Terrestrial habitats 
Following a W-E direction, this ecoregion features the Cordilleran mountain area with 

the highest mountains of the American Continent, such as Mt.  Aconcagua with 6,959 m 
(Mendoza province) and Mt. Mercedario with 6,770 m (San Juan province); eastwards, 
the Precordillera (Subandean ranges), and in the east,  arid plains, sometimes called 
‘travesías’, with some isolated hills that belong to the Pampean orographic system. The 

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plant communities that grow in  this area are poorer than in the so-called ‘Monte de 
Sierras y Bolsones’ biome; these two are considered as the most xerophytic of 
Argentinian biomes.   

In the provinces of La Rioja and San Juan, the valleys that lie between the mountains 
originate plains with little slope (depressions) where some basins with poor or non-
existent drainage (known as ‘bolsones’) develop. In these areas the dominant plants are 
species of Larrea, along with ‘retamo’ (Bulnesia retama), ‘pichana’(Cassia aphylla), ‘brea’ 
(Cercidium praecox), and others that conform the typical ‘jarillal’ (Creosote bush) 
community (Monte de Sierras y Bolsones). 

The Chaco Seco (see description of terrestrial habitats in Central Endorrheic 
ecoregion is also represented in the eastern sector of La Rioja province. 

Aquatic habitats 
The Desaguadero river basin that crosses the ecoregion arises in the border between 

the provinces of Catamarca and La Rioja, at about 6,000 m above sea level, and it covers  
30 % of La Rioja, 90 % of San Juan, 50 % of Mendoza, the western border of San Luis 
and part of La Pampa.  Several dams have been built along the course of this system. 
There are also some small streams, often temporary (e.g. the Bermejo or Vinchina  river 
in La Rioja). 

Some of the fluvial systems have undergone artificial interconnecting of their courses 
for better exploitation of their flow, e.g. the canals that connect the middle courses of  
Mendoza and Diamante rivers to Tunuyán and Atuel rivers respectively. 

Mendoza and San Juan rivers feed the Guanacache lacustrine system, which has a 
length of  about 200 km and a surface area of some 5,800 km2. This system was once an 
important center for fishery activities (Larrain, 1906, In: Villanueva & Roig, 1995; Bucher & 
Chani, 1998). Throughout the years it suffered diverse anthropogenic impacts and the 
effects of climatic cycles, which altered the water levels; the system was receding until 
1998, but at present it has entered a recovery stage.  

Llancanelo lagoon, situated to the southwest  of Mendoza province, occupies an 
ecotonal area between the biogeographical provinces of Monte, Andean and Patagonic, 
receiving faunistic and floristic elements of pampean, Andean and subandean origin 
(Iglesias & Pérez op.cit.) 

Biodiversity  
Mendoza river: 9 species (2.0 %). 
Main collector for Desaguadero system: 8 species (1.8 %). 
Tunuyán river: 6 species (1.4 %). 
San Juan river: 3 species (0.7 %). 
Tributaries of Chilecito valley (La Rioja province): 2 species (0.5 %). 
Jáchal river: 2 species (0.5 %). 
Diamante river: 1 species (0.2 %). 
Atuel river: 2 species (0.5 %). 
Bermejo de La Rioja river (La Rioja province): 1 species (0.2 %). 
Tributaries to Llancanelo lagoon: 4 species (0.9 %). 
Occurring families: Table 2. 

The distinctive ichthyofaunistic elements are families Diplomystidae and 
Percichthyidae, which are endemic for the Neotropica and reach their southernmost 
distributional range within this ecoregion. Among the Ostariophysi, there are 
representatives of orders Characiformes, with genera Astyanax and Cheirodon; and 
Siluriformes, with the endemic species Diplomystes cuyanus, Trichomycterus alterus, T. 
heterodontum, T. riojanum and Silvinichthys mendozensis  (Tables 2 and 6). In addition, 

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there are species of orders Atheriniformes, Cyprinodontiformes (Jenynsia pygogramma), 
Synbranchiformes, Perciformes and exotic Salmoniformes. To sum up, the Subandean-
Cuyan ecoregion has presently  20 recorded species distributed among eight families, 
four of them exotic (Tables 2 and 3). 

Ichthyofaunistic remarks 
The presence of a species of order Synbranchiformes in the central-southern areas of 

San Juan province (Murúa & Acosta, 1995) supports the pressumption that Synbranchus 
marmoratus might inhabit the area of Guanacache lagoons (Mac Donagh, 1950; Rusconi, 
1961, In: Villanueva & Roig, 1995) and in Meré lagoon (coast of Araujo, in Lavalle, 
Mendoza province) (H. Sosa, pers. comm.). The record in San Juan (31°37’S, 68° 30’W) 
is the westernmost reference for this species, which constitutes yet another Paranensean 
element in the Subandean-Cuyan Ichthyogeographic Province. The system of 
Guanacache lagoons, according to the zoogeographical outline for Mendoza province 
(Roig & Contreras, 1975), are part or the so-called “Fauna of aquatic and halophyle 
environment”. The presence of S. marmoratus within these brackish habitats suggests 
that the species may have currently unidentified special ecophysiological traits  (see 
Cione & Barla, 1997). In addition to the exotic species that have been introduced and are 
discussed below, the 'Bonaerensean Silverside' (Odontesthes bonariensis) has been 
transplanted into this ecoregion.  
Vulnerable species: the intense exploitation of the watercourses for different purposes, 
such as irrigation, dams, etc., represents a  threat for the entire aquatic life  in the area, 
which is occupied by the Diplomystidae and Percichthyidae,  endemic Neotropical families 
forming a group with particular ecological adaptations. With   respect to the diplomystid 
catfishes, their biology and ecology are poorly known, as most of the research about the 
group has been focused on phylogenetic issues (Arratia, 1987, 1992). Arratia et al. (1983) 
state that the distribution of family Percichthyidae is not clear due to the management 
implemented by governmental organizations, and add that ‘Ultimately, the limit of the 
natural distribution of Percichthys in Argentina extends more towards the south than it 
does in Chile’. 

Biological value 
It comprises some of the “areas of outstanding biodiversity” of  Monte biome. 
Llancanelo lagoon possesses very diverse and numerous avifauna (Sosa, 1995; 

Martínez et al., 1997). It is also a nesting area for its most representative species, the 
common flamingo (Phoenicopterus chilensis). The rodent Tympanoctomys barrerae, 
found in this area, inhabits halophyle areas and is endemic to Mendoza province.  

The Guanacache lacunar system is situated in an ecotonal area between the Chacoan 
region and the desertic areas that occupy the west of Argentina. 

Impacts/Threats 
Advance of agropecuary activities; alteration of watercourses (hydraulic works, dams 

such as El Nihuil and Valle Grande); habitat fragmentation; inadequate management and 
destruction of the vegetation of the basin; unregulated tourism/recreation; urban 
conglomerates; resource overexploitation; oil extraction, mining and industrial activities; 
poaching; consumptive water extraction (e.g. from Malargüe river, that feeds Llancanelo 
lagoon).  

In addition, the presence of exotic species such as Cyprinus carpio, Ctenopharyngodon 
idella, Carassius auratus and Oncorhynchus mykiss (Table 3).  

National Protected Areas 
San Guillermo National Park (San Juan province). 
Western sector of Sierra de las Quijadas National Park (San Luis). 
Talampaya National Park (La Rioja). 
El Leoncito Strict Natural Reservation (San Juan). 

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Ramsar Sites 
Llancanelo lagoon (Mendoza). 
Guanacache lagoons (San Luis, San Juan and Mendoza). 

Correspondence 
Wetlands: Regions 2 and 4. 
Ecoregions: Altos Andes, Monte de Sierras y Bolsones, Monte de Llanuras y Mesetas. 
Zoogeography: Central or Subandean Domain, Patagonic Domain. 

Rationale 
The elements that validate the proposed ecoregion are the following:  

♦ Presence of endemic families such as Diplomystidae and Percichthyidae, which occur 
exclusively in South America and reach their southern distributional limit within this 
ecoregion (San Juan province) at about 31° S. 

♦ The basal phylogenetic position of the Diplomystidae that supports the high-priority 
conservation interest (Stiassny & Pinna, 1994).  

♦ Presence of one endemic genus and species of Trichomycteridae, Silvinichthys 
mendozensis. 

♦ The ecotonal character of the eastern and southeastern portions of this ecoregion, in 
the areas occupied by Guanacache and El Rosario lagoons, and Llancanelo lagoon, 
respectively. 

♦ Presence of Odontesthes hatcheri,  an endemic Atherinopsidae that also occurs in 
Chile. 

Relevant Bibliography 
Wernicke (1932); Peñafort (1981);Villanueva et al. (1992); Arratia (1998). 

10) PATAGONIAN ECOREGION 
Limits  

To the N it’s bound by the Subandean-Cuyan ecoregion and an imaginary line that 
runs in west-east direction from the northern limit of the Colorado river basin, bordering 
the "no-records" hiatus situated in the north-center portion of the province of La Pampa 
and continuing eastwards until reaching the Atlantic coast at Verde peninsula 
(approximately 39°30’S, 62° 10’W). To the E, the ecoregion is limited by the Atlantic 
ocean. To the W, the Andean heights establish the watershed separating the Pacific 
drainage watercourses (not included).  

Description 
The Argentinian Patagonia is situated south of Colorado river, bound to the west by the 

Andes mountain range and  to the east by the Atlantic Ocean. Patagonian relief is not 
even; the moderately high mountain range that extends in N-S direction is the most 
conspicuous geomorphologic feature. In their middle section and eastwards, the 
mountains lose height and give way to hilly elevations, and finally blend with the 
Patagonides orographic system. Nevertheless, the major morphological unit corresponds 
to the plateau. This doesn’t have a regular surface but has many different aspects: the 
extensive plains that receive the name of pampas (e.g. Pampa del Castillo, Chubut 
province, at 1,000 m above sea level); the sierras, with heights ranging from 1,000 to 
1,800 m.; the river valleys (called ‘cañadones” when they are dry) that cross the plateau in 
W-E direction; and the lowlands known as ‘bajos’ (the great lowland in Valdés Peninsula, 
situated 45 m under sea level).  

The geomorphology of the area is the result of a complex geological history, due to the 
Pleistocene glaciations that affected severely the middle latitudes in South America. By 

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the end of that geological period, the climatic warming fostered the formation of many 
lakes along the Andes mountain range. These lakes, that can have tectonic, periglacial, 
volcanic, eolic or karstic origins (Markgraf, 1988) range from shallow to deep, and from 
intermittent to permanent. Those of periglacial and volcanic origin are situated close to the 
Andes, while those of eolic erosion origin are found in extra-Andean Patagonia. Aluminé 
lake (Neuquén province) is the first in the series of cordilleran lakes, among which we may 
mention lakes Nahuel Huapi, Buenos Aires and Fagnano, the latter shared with Chile.  

In the mountain area of Santa Cruz province there are immense glaciers such as Perito 
Moreno, with a front area 5 km wide and 60 m high. 

The eastern part of Grande de Tierra del Fuego island is occupied by the Argentinian 
province of Tierra del Fuego, bordered by the Argentinian Sea (Atlantic Ocean) and 
separated by Beagle channel from several Chilean island situated southwards. This 
province has moderately high plateaus in the north and center of the territory, and the 
south part is occupied by an extension of the arid Andes creating a mountainous relief.  
Surface area: 756,400 km2. 

Terrestrial Habitats 
The dominant plant communities are shrubby steppes, while the more humid regions 

are occupied by  cushion plants and grassy steppes. In the valleys where the small 
streams form bogs, dense graminaceous and cyperaceous prairies called ‘vegas’ grow 
along with other herbaceous plants. In the areas of low saline soils the plants are 
halophyte and generally  have succulent leaves.  

The subpatagonian (also called subantarctic or Andean-patagonian) forests develop in 
a narrow area along the mountain slope from the northern regions of Neuquén province 
extendind to Tierra del Fuego and Estados island. The dominant plant formation is a 
semideciduous temperate-humid forest. To the north this assemblage is replaced by the 
Chilean Valdivian Forest with several characteristic tree species such as Araucaria 
araucana and Nothofagus species. 

Aquatic Habitats 
This ichthyogeographic province is included in the categories Ríos interiores sin 

derrame al mar and Ríos de vertiente atlántica  (Mazza, 1961) and Región III – Ríos 
de vertiente atlántica de la Subregión Patagónica Chilena (Bonetto, 1998). Some of 
the lotic water courses arise in complex headwaters situated in the Andean macizo and 
then become connected with lesser water courses and, in some cases, with oligotrophic 
lakes. These courses pass onto the Patagonic plateau, where they don’t receive any 
tributaries, and finally flow into the Atlantic ocean (e.g. Negro river). There are also 
endorrheic basins, wide oligotrophic lakes (such as Nahuel Huapi, Fontana, Fagnano, 
etc.) and impoundments such as Alicurá, Florentino Ameghino, etc. (see Calcagno et al., 
1995). In addition, the Vertiente Pacífica (Mazza, 1961) or Pendiente del Océano 
Pacífico (Daus, 1975) comprises a fluvio-lacustrine system arising on the eastern slope 
within Argentinian territory and draining into the Pacific ocean in Chile (e.g. lakes Lácar, 
San Martín and Fagnano). 

According to Baigún (2001) there are three groups of lakes: 
1) Oligotrophic Andean lakes, which are stratified and have low conductivity (including 

the large very deep lakes), and shallow lakes, which are never stratified, have 
higher conductivity and low transparency.  

2) Ecotonal lakes, situated in Andean and Subandean spurs; these are very deep, 
never stratified, meso- to eutrophic and have moderate to high levels of nutrients 
and conductivity.  

3) Plateau lakes and impoundments, with two types: a) deep, oligotrophic and with 
summer stratification; b) large lakes and impoundments with moderate depth, 

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generally non-stratifying, with high levels of nutrients and conductivity and low 
transparency. 

Biodiversity  
Colorado river: 13 species (2.9 %). 
Negro river: 12 species (2.7 %). 
Chubut-Senguer