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Fish Fauna and Environments of the Pilcomayo-Paraguay Basins in Formosa, Argentina

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Fish Fauna and Environments of the Pilcomayo-Paraguay Basins in Formosa, Argentina Hydrobiologia 245: 129-146, 1992. © 1992 Kluwer Academic Publishers. Printed in Belgium. 129 Fish fauna and environments of the Pilcomayo-Paraguay basins in Formosa, Argentina Roberto C. Menni 1, Amalia M. Miquelarena 2, Hugo L. Lopez 2, Jorge R. Casciotta2 , Adriana E. Almiron & Lucila C. Protogino 2 1Laboratorio de Ictiologia, Museo de La Plata, Paseo del Bosque s/n, 1900 La Plata, Argentina; 2 Instituto de Limnologia de La Plata, 53 N 484, 1900 La Plata, Argentina Received 16 July 1991; in revised form 1 April 1992; accepted 28 April 1992 Key words: fish zoogeography, ecology, water chemistry, faunistics, Argentina Abstract The ichthyofauna from subtropical (East) and tropical (West) areas in the Formosa province (North- ern Argentina) is analyzed. An up-to-date list of fishes is provided, including 18 new reports for envi- ronments associated with the Pilcomayo and Paraguay rivers, considering the detailed distribution of the fishes. Dominant families in terms of number of species are Characidae, Pimelodidae, Loricariidae and Curimatidae. Percentage of individuals (about 5000 examined) were 66% for characoids and 25% for siluriforms, with less than 10% for other groups. Comparisons were made with other South American environments. Most frequent species were Psellogrammus kennedyi, Astyanax bimaculatus, Gymnocorymbus ternetzi, Hoplosternum thoracatum and Cichlasomaportalegrense. The predominant type of environment sampled, of small size and shallow depth, with extensive plant cover, and temporal level variations, explains the dominance of the above groups. This interpretation is supported by independent studies. Diversity values ranged between 0.71 and 3.92. A marked reduction in number of species from East to West was observed (79 and 41 species respectively, 31 shared). No species of Gymnotidae, Hemiodidae, Characidiidae, Trichomycteridae, Lebiasinidae nor Aspredinidae were captured in the West. The higher number of species in eastern environments is considered to be due to the influence of the Paraguay river and the complex hydrology of the area. Other factors, both historical and ecologi- cal are considered. A correlation between total phosphorous content in the water and fish richness is also suggested. Water chemistry is compared with near by environments. Sites studied showed pH values from 6.14 to 7.5. The dissolved solid contents ranged from 51.8 to 474.3 mg 1- ', within the hypohaline level. Ionic composition differed somewhat between East and West, water in the East being mainly hypocalcic, as in the Paraguay river. Conductivity was rather variable and Secchi disk values similar to those in the Parana river. Introduction Bermejo river to the South, the Paraguay river to the East, and about 64 ° W to the West (Figs 1 Formosa is a province in northeastern Argentina, and 2). Most of its territory is subtropical except between the Pilcomayo river to the North, the for a small NW sector within the tropical belt. 130 Fig. 1. Localities samples in Eastern Formosa (1-17 + 18 and 19 from MLP). The insert shows the Formosa province in Argen- tina, and the Eastern (1) and Western (2) areas. 131 the tropics, corresponds to the 28-29 C iso- therm in summer (January the warmest month), and to the 17 C isotherm in winter (July the coldest month). The E zone has respectively the following values: 27-28 °C and 17 °C. Both areas are frost free over 340 days yr- . Total an- nual rainfall is between 700 mm y-' in the NW and 1100 mm y- 1 in the E. Bucher (1980) maintains that the most impor- tant factors for the terrestrial fauna (rainfall, sea- sonality, soil type) show a well defined E-W gra- dient which has a stronger influence over the biota than the weak N-S temperature gradient. The climate is subtropical with a dry season (in win- ter) at the center and in the West, and a small stripe without a dry season in the East (Chiozza & Gonzalez van Domselaar, 1958). Many eco- logical aspects of the area can be seen in Neiff (1986). The area studied belongs to the La Plata river Fig. 2. Localities (22-30) samples in western Formosa. basin, zoogeographically within the Paranoplat- ensean province in the sense of Ringuelet (1975). Though it is presumed to be a rich fish zone, available information about the number and iden- The territory of the province is part of an enor- tity of the fishes is fragmentary and scattered. The mous pluvial valley without elevations, so the re- most comprehensive data on the ichthyofauna of lief is determined by alluvial deposits. The general this area influenced by the Pilcomayo and Para- slope is in a NW-SE direction, with a similar guay rivers are provided by Ringuelet et al. (1967), pattern in the orientation of rivers and creeks. who reported 84 species from localities in For- The low slope conditions the water runoff. Ac- mosa. Other references have been provided by cording to Siragusa's (1975) hydrographic Lopez & Castello (1966), Castello et al. (1978), scheme, the lakes, 'lagunas' and salines of the Azpelicueta & Braga (1980), Lopez (1972, several area belong to the 'Chaquean' province, agreeing species) and Bayley (1973). Pignalberi de Hassan in general terms with other geographic and phy- & Cordiviola de Yuan (1988) provide a list of togeographic criteria (Bucher, 1980; Cabrera, 76 species (some synonyms excluded). 1976). Considering main characteristics of the For the present paper 30 aquatic environments soil, the NW section is called the Flooding zone related to the Pilcomayo and Paraguay rivers were of the Pilcomayo river (Fig. 2), and the E section surveyed in the Formosa province (Figs 1 and 2). the Eastern depression (Morgan, 1980) (Fig. 1). Samples are divided according to the above men- This eastern zone is, according to Neiff(1986), an tioned zones, with 6 localities in the Flooding extensive system of autochthonous rivers with a (Western) zone (Fig. 2) and 17 localities in the surface area of nearly 82 700 km 2. Within this area Eastern depression (Fig. 1). there are only two allochthonous rivers, the Pil- The aim of the paper is to provide an up-to- comayo and the Bermejo, which transport sedi- date list of the fishes occurring in the Formosa ments from the eastern slopes of the Andes. After province, analyse the distributions of 18 species Burgos (1970), who describes in some detail the which are new for the area, and to report and climate of the area, the NW zone, mainly within discuss limnological observations. 132 Material and methods Table i. (Continued) The studied material Loc. 3. A man-made pond at the crossing of the national was gathered from: route 11 with the road to Tte. Gral. J. C. Sanchez ( = Riacho a) 23 localities sampled by the authors (RCM, He-He), 27 km far from Clorinda, Pilcomayo Dept. HLL, JRC) during August 1986 (steady wa- Loc. 4. * A man-made pond along the secondary road from ters at the end of dry period) and April 1988 the national route N 11 to Tte. Gral. J. C. Sanchez, km 884, (about the end of the rainy period). Of these, Pilcomayo Dept. Astyanax fasciatus, 1 spec., 27-VIII-90-2. Hyphessobrycon luetkeni, 1 spec., 20-IX-90-1. Moenkhausia 17 belong in the Paraguay and Pilcomayo riv- sanctafilomenae, 1 spec., 20-IX-90-2. Tridentopsis pearsoni, ers basins in the East of Formosa (Locs. 1 to 1 spec., 27-VIII-90-1. Apistogramma borelli, 3 spec., 24-VIII- 17, Fig. 1), and 6 belong in the Pilcomayo river 90-6. basin in the West of the province (Locs. 23 to Loc. 5. A man-made pond along the secondary road from the 28, Fig. 2). national route N 11 to Tte. Gral. J. C. Sanchez, km 892, Pil- b) 5 localities were obtained from material in the comayo Dept. Rhamdia cf. quelen, 2 spec., 24-VIII-90-7. collection of the Museo de La Plata (MLP), Loc. 6. A man-made pond along the secondary road from the collected before this work was done (Locs. 18 national route N 11 to Tte. Gra. J. C. Sanchez, km 896, Pil- to 22; 18 and 19 in the East, 22 in the West, comayo Dept. Astyanax fasciatus, 15 spec., 29-VIII-90-1. 20 and 21 imprecise so not on map). Hyphessobrycon luetkeni, 2 spec., 25-IX-90-1. Rhamdia cf quelen, 3 spec., 29-VIII-90-2. Tridentopsis pearsoni, 1 spec., c) 3 localities in the Pilcomayo basin, with ma- 25-IX-90-2. terial gathered by Toba-Pilaga indians from Loc. 7. A creek under the first bridge in the road from Tte- Vaca Perdida and El Churcal offered by Mr. Gral. J. C. Sanchez to Colonia Pastoril, km 921, Pilcomayo Pastor Arenas (CONICET) (Locs. 23, 29, Dept. Astyanax fasciatus, 1 spec., 25-IX-90-3. Disichthys and 30). iheringi, 1 spec., 30-VIII-90-1. Moenkhausia intermedia, 1 spec., 25-IX-90-4. Samples of fishes which are new reports for the area are deposited at the MLP, together with de- Loc. 8. * A creek crossing the national route N 11, km 103, 36 km far from Clorinda, Pilcomayo Dept. Astyanaxfasciatus, tails of species and number of specimens caught 2 spec., 30-VIII-90-3. Hyphessobrycon luetkeni, 1 spec., 25-IX- at each locality. 90-5. Moenkhausia intermedia, 1 spec., 25-IX-90-6. Geographical information under each new re- M. sanctafilomenae, 4 spec., 30-VIII-90-5. Characidium port includes the most comprehensive references fasciatum, 3 spec., 30-VIII-90-4. Rhamdia cf quelen, 5 spec., and other of particular interest (A full references 30-VIII-90-2. list is not given for editorial reasons). Table 1 lists Loc. 9. * Riacho (small river) Timbo-Pora.
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