Fish assemblage attributes in a small oxbow lake (Upper Paraná River Basin, São Paulo State, Brazil): species composition, diversity and ontogenetic stage

CARVALHO¹, E.D.; MARCUS¹, L.R.; FORESTI¹, F. & SILVA², V.F.B.

¹ UNESP, Institute of Biosciences, Department of Morphology, Fish Biology and Ecology Laboratory, 18618-000, Botucatu, São Paulo State, Brazil. e-mail: carvalho@ibb.unesp.br ;

² Department of General Biology, UEMS, Mundo Novo, CEP 79980-000 - Mato Grosso do Sul State, Brazil.

ABSTRACT: The composition and diversity of fish species in a seasonally isolated small oxbow lake (area = 8,592 m²), located in the transition zone between the Paranapanema River and the Jurumirim Reservoir (São Paulo State, Brazil), was studied from July/ 1998 to June/1999. Fish samples were taken monthly using three gear types: a 0.5mm-mesh sieve of 0.89m² in area; a seining net (width = 1.40m, length =10.0m, mesh size = 5mm); and gill-nets (1.5 – 3.5 cm between adjacent knots). Species composition and some ecological attributes (diversity, evenness, species richness) were determined for the study period (rainy and dry seasons), using the three gears. Fish caught in all gears were separated according to life stage (larvae, juvenile and adult). Some abiotic and environmental variables were determined in order to verify their correlation with the seasonal distribution of life stages in the study site. Species composition in this lake comprised four orders (Characiformes, Siluriformes, Gymnoformes and Perciformes), 11 families, 21 genera and 24 species. A total of 5,481 individuals were collected with a total weight of 27.53 kg. Characiformes dominated the samples. The Characidae species Serrapinus notomelas and Cheirodon stenodon, prevailed in number whereas the species Cyphocharax modestus, Hoplosternum littorale, Pimelodus maculatus, Prochilodus lineatus and Hoplias malabaricus predominated in weight. There were statistical differences between the dry and rainy seasons only for samples captured with seining net and gill-nets, with the latter presenting greatest diversity, evenness and species richness. A significant relationship among some abiotic variables (dissolved oxygen, suspended solids and conductivity) and biotic variables (life stages) were indicated by the first canonical function. In conclusion, the lentic zones formed by lakes and floodplains, which are found near big rivers, may seasonally offer ideal conditions, such as food and shelter, to most river fish species and thus, play an important role in sustaining the trophic network and increasing fish yield in the different ecosystems of riverine systems.