The freshwater fishes are threatened by anthropic disturbances. Our study investigate the trends of a retrospective analysis and the changes on the structure of fish assemblages in a tropical reservoir. To attempt it, we compared scientific publications of Lobo-Broa reservoir from 1975 to 2011, integrating long-term environmental data. The results obtained suggest the composition of species had an increase in similarity. The species with higher constancy of occurrence became constant, reflecting an increased constancy of opportunistic species with a declining number of native species. In conclusion, our study are an important register and alert about the anthropic impacts on fish assemblages, supporting the implementation of fishery management and conservation acts.