Fish assemblage dynamics in a shallow floodplain lake in the South of Brazil

MALTCHIK¹, L.; MÜLLER, D.A. & STENERT, C.

¹Laboratório de Ecologia e Conservação de Ecossistemas Aquáticos, Universidade do Vale do Rio dos Sinos, CEP 93022-000, São Leopoldo, RS, Brasil; e-mail: maltchik@.unisinos.br

ABSTRACT: The flood pulse concept suggests that the flood is the principal driving force responsible for the existence, productivity and interactions of the major biota in river floodplain systems. The main goal of this study was to analyze the effects of the floods events and abiotic variables (water temperature, depth, conductivity and transparency) on the fish composition, length, abundance, richness and diversity in a shallow floodplain lake over an annual cycle (2000-2001). Fourteen fish collections were carried out and fishes were sampled using electrofishing equipment. A total of 3,103 individual fish representing 25 species in six families was collected. The Characidae family (12 species) comprised 90.7% of sampled individuals. The fish abundance and richness increased along the annual cycle and the flood events contributed to it. However, the percentage of change on fish numbers and richness was not related with the flood duration. Water temperature, depth, conductivity and transparency influenced fish abundance and richness. The mean length of the six more abundant fish species over the studied annual cycle (representing 91.62% of the total number of collected fishes) was below the estimated length for the first gonadal maturation, showing that the majority of the collected fishes were juveniles. Our results confirm the hypothesis that the floodplains are crucial habitats for the development of juveniles and for the recruitment of the fish assemblages in the South of Brazil.

Key-words: floodplain, flood pulse, fish assemblage, recruitment, Neotropical region.