The freshwater fishes are threatened by anthropic disturbances. Modification of natural patterns of fish biodiversity are often coincident with the environmental degradation, introductions of non-native species and the biotic homogenization. Our study investigated the trends of a retrospective analysis and the changes on the structure of fish assemblages in a tropical reservoir. To attempt it, information between the 1970's to 2010's decades of Lobo-Broa reservoir were compilated, integrating long-term environmental data. The results obtained suggest the composition of species had an increase in similarity, being referred as a biotic homogenization process. Thus, 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 reported the anthropic impacts on local fish assemblages' changes and homogenization that can increase species extinction risk. This long-term environmental monitoring is an important alert about the ecological risks and uncertainties posed by anthropic disturbances, supporting the development of fishery policy and management on the regional and global conservation.