Amalia María Miquelarena

Fish and limnology of a thermal water environment in subtropical South America

Two thermal sources with water temperatures from 51 to 59°C flow into a stream of 2 to 5 m width and about 0.5 m depth at Agua Caliente (23° 44′, 64° 38′) in Jujuy province, Argentina. Data from 3 years sampling show that the influence of the thermal sources maintains the water temperature of the stream section at a high and constant level (from 24 to 35°C), different from the thermal regime of other streams in the area. Composition of water (N=13) has the following mean values: pH 8.36, conductivity 1591 µS cm-1, dominant ions (in mg l-1) CO3-- 12.77, CO3H- 140.27, Cl- 246.86, SO4-- 460.14, Na+ 400.45, K+ 2.18, Ca++ 27.68 and Mg++ 2.14. Mean total dissolved solids: 1.3 g l-1. Large amounts of SO4--, Na+, and Cl- Sixteen fish species (2460 specimens) were captured in the warmed reach. Dominant families were Characidae, Cichlidae and Loricariidae. New geographic distribution information is provided for eight species, some of them with restricted northwestern Argentina distributions. Most abundant species were the eurytopic characid Astyanax bimaculatus, followed by the cichlid Bujurquina vittata. These species have the highest critical thermal maximum according to field experiments. Temperature of acclimatization is closer to lethal than in fishes from ‘normal’ habitats. Agua Caliente differs from other thermal habitats in the lack of isolation, its placement in a rain forest area, a high number of species, and the lack of cyprinodontoids. The fish fauna here represents an opportunistic invasion of a habitat with water parameters strongly different from those in the area, particularly temperature and salinity. Both faunistic and limnological traits make of Agua Caliente a new type of environment within the subtropics.

Fish fauna and environments of the Pilcomayo-Paraguay basins in Formosa, Argentina

The ichthyofauna from subtropical (East) and tropical (West) areas in the Formosa province (Northern Argentina) is analyzed. An up-to-date list of fishes is provided, including 18 new reports for environments 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 Cichlasoma portalegrense. 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 ecological 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 1−1, 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.

Nuevas localidades para peces de agua dulce de la argentina: IV. Adiciones a la ictiofauna del río uruguay y algunos afluentes(1)

From 58 species collected in the Uruguay river and some of its affluents, new localities are reported for six Characoidei species (Schizodon platae, Glandulocauda terofali, Holoshestes pequira, Hyphessobrycon luetkeni, H. meridionalis and Aphyocharax rubropinnis) and for three Siluriformes (Megalodoras laevigatulus, Auchenipterus nuchalis and Bunocephalus ihe‐ringi). For these nine species morphological data and complete Argentine references are given. Chemical data on the affluents are checked with those from neighbouring areas.

Fishes and environment in northwestern Argentina: from lowland to Puna

The fish fauna and its relationships with physiography and climate were studied in northwestern Argentina from 21°30′ S to 26°30′ S and 63°30′ W to 65°50′ W, an area about 10,276 km2. Along a southeast–northwest gradient, the Chaco forest at low altitudes gives way to the Yungas cloud forest in highlands, and then, to an increasing desertic landscape, with xerophytic vegetation and scarce rainfall along the Grande River. Finally, extreme desert conditions prevail in the most northern part at the Puna plateau. Water chemistry was sampled from sites from 400 to over 3800 m a.s.l. In all 3278 fish specimens of 52 species were collected. Previous lists included 84 species. Only 19 were shared, meaning that 40 species are new for the area and/or particular localities, including 7 reports from Aguas Calientes. These results increase by one third the number of species in northwestern Argentina. The fish fauna was represented by eurytopic species of Paranensean genera as Astyanax, Bryconamericus and other characoids, mixed with locally distributed siluriforms. Under extreme climatic conditions, species of Trichomycterus predominate. Species assemblages show a combination of a large number of species typical of, sometimes endemic to or rather abundant in, the area, combined with a few species of Paranensean character. Fish assemblages were clearly defined by faunistic composition and distribution related with physiography and climate traits. A significant negative correlation is observed between both species number and abundance, and increasing altitude, and positive relationships exist with mean annual temperature and other climate traits. Diversity values (Shannon index) agree with the described pattern of increasing impoverishment of the fish fauna of northwestern Argentina, along gradients of increasing altitude and dryness and decreasing temperature.

Hyphessobrycon nicolasi (Teleostei: Characidae) a new species from the Uruguay River basin in the Mesopotamian Region, Argentina

Hyphessobrycon nicolasi is described from the Uruguay River basin in the Mesopotamian Region, Entre Rios, Argentina. The new species can be distinguished from all congeners by the presence of a well-defined oblique and marginal black stripe on each lobe of the caudal fin. Other characters defining H. nicolasi are the possession of 1-3 teeth with 3-10 cusps on maxilla; outer premaxillary row with 2-3 small teeth, with 5 or 7 cusps; iv-vi, 27-36 anal-fin rays; 33-36 scales on the longitudinal series; two vertical dark spots on the humeral region; dorsal and anal fins dappled in black and base of caudal fin bearing conspicuous black spot; and the presence of bony hooks on the rays of dorsal, anal and caudal fins of the mature males.

Cyanocharax alburnus (Hensel, 1870) (Characiformes: Characidae): First distribution record in Argentina

This note reports the presence of Cyanocharax alburnus in the Argentinian Mesopotamia. This represents the southern distributional limit for the species in South America and the first record for Argentina’s fresh water fish fauna.

Actinopterygii, Characiformes, Characidae: Ectrepopterus uruguayensis (Fowler, 1943): new record for Argentina

Ectrepopterus uruguayensis Fowler was recently redescribed, with occurrence in lower tributaries of Rio de la Plata and lower Rio Uruguay, Uruguay. Herein its occurrence is extended and confirmed to Argentina, arroyo El Molino, in Uruguay Department, Entre Rios Province, Uruguay drainage.