TROPHIC STRUCTURE OF FISH ASSEMBLAGES OF RIO-SAO-JOAO, RJ, BRAZIL

Qualitative changes in the trophic structure of the Sao Joao river fis h fauna were studied. Fishes were collected monthly from January/92 to December/92 in 6 sample units. During samples, seven physical variabl es (river order, width, depth and slope, water velocity and salinity a nd pluviosity) were measured. Thirty specimens of each species were di ssected for gut contents analysis, which aimed to cluster the differen t taxa into trophic guilds. Temporal variability in the trophic struct ure of the communities was studied applying similarity indices and clu ster methods. Eighty-eight species were collected and 62 were used in the trophic analyses. Twelve trophic guilds were recognized. Positive correlation was obtained between the number of guilds and the river or der, whereas negative correlation was identified involving guild richn ess and the river slope. Trophic stability, complexity and resilience were strongly correlated with the river slope, order and dimensions.