The Paraíba do Sul is a major running water system in southeastern Brazil (22º24' -22º26'S; 43º43' -44º16' W), draining one of the most important industrial regions in the country. Because of its location, it has suffered a large amount of alteration due to discharges of urban and industrial effluents with direct influence in the ichthyofauna. The aim of this study is to up-to-date information on fish assemblage structure and its variation in the vicinity of a major industrial effluent outfall at Volta Redonda industrial complex. A standardized fishing sampling program, using seines, casting nets, gill nets and net trays, was carried out from October 1997 to September 1999, at six sites in three zones of the river (upstream, nearby and downstream the industrial complex), aiming to compare variation in fish assemblage due to anthropogenic alteration. Fifty-two species in 13 families were identified in the total of 7286 fish specimens. Characidae was the most diverse family contributing with 28,85% to total number of species, followed by Cichlidae (17,31 %). Overall 15,38% of the species were introduced from other watershed systems, four exotic cichlids (genera Oreochromis Günther, 1862 and Tilapia A. Smith, 1840) and three aloctone (Cichla ocellaris Bloch & Schneider, 1801, Hyphessobricon callistus (Boulenger, 1900) e Metynnis maculatus (Kner, 1860)). Lebistes reticulatus (Peters, 1859) was the most abundant fish species contributing to 39,7% of the total number of fish, followed by Geophagus brasiliensis (Quoy & Gaimard, 1824) amounting to 27,4%. Fish abundance was higher in the industrial zone, but only a few very dominant species were captured, while the upstream zone showed the most even community. Species replacement tolerance along the alterations gradient in the three zone seems to be a strategy to use the limited resources in the area.
Rivers; fish taxocenose; pollution; ichthyofauna; fish ecology