The role of salinity in structuring the fish assemblages in a tropical estuary.

The present study describes the seasonal changes of the fish species composition in three areas of the main channel of the Caeté River estuary, Brazil. The fish faunas of each habitat differed in density, biomass and species composition. Mean fish density and biomass for the Caeté River estuary channel was 0·25 individuals m−2 and 0·9 g m−2 respectively. Analysis of catch data showed that the number of species, total density and total biomass differed significantly between areas and seasons. For the most important species, the mean density ofCathorops spixii, Aspredinichthys filamentosus, Aspredosp. 2,Pimelodus blochii, Pseudauchnipterus nodosusandMacrodon ancylodon, differed significantly between seasons while the mean density ofStellifer rastrifer,Stellifer microps, Aspredo aspredo,Aspredosp. 1 andCynoscion acoupadid not. The mean biomass of these species, with exception ofS. micropsandAspredosp. 1, also differed significantly between seasons. In the Caeté estuary seasonal salinity fluctuations appeared to be the main factor that structured the fish assemblage in the entire estuarine system. At least 85% of the species captured by the artisanal and subsistence fisheries in the Bragantine region required estuarine conditions to complete their life cycle. [ABSTRACT FROM AUTHOR]