Environmental Assessment Through the Biotic Integrity Index of Guaíba Lake, Rio Grande do Sul, Brazil

This work aimed to test an adaptation of the Biotic Integrity Index (BII) of in fish assemblages in the environmental monitoring. The fish samplings were standardized and performed seasonally during two years, using seine nets in eleven points of the hidrographic basin of Guaíba lake, Brazil. The results showed that the analyzed points were rated as regular or poor in terms of quality. The scores obtained by BII for the points Gasômetro and B. Ribeiro contradict the results obtained by main components analysis with physico-chemical parameters of the water. The parameters that most influenced the BII results for the points to be rated as fair in terms of quality were the species richness, the number of individuals, the percentage of individuals infected with black spot disease and the percentage of individuals with morphologic alterations. This paper discusses the fragility of the calculation method used to establish the categories of best, medium and low quality. These data demonstrate that other factors may be contributing to the water quality decrease. This study indicated the need to use more than one methodology as an instrument of the environmental quality evaluation.