Swimming performance of fish constitutes a good ecophysiological tool to evaluate the ability of species to use different types of habitats. In order to understand how the swimming performance is related to the hydraulic environment, we compared the critical velocity of five fish (Characidae): Stygichthys typhlops (groundwater troglobiotic); Piabina argentea and Bryconamericus stramineus (riverine); Hemigrammus marginatus (generalist, found in rivers and floodplains) and Psellogrammus kennedyi (lacustrine). Swimming speed tests were performed in a respirometer-type apparatus. Total body length was the variable that best explained the maximum speed attained by all species under study. The critical swimming speed values (in body lengths per second) for each species were as follows: P. argentea (13.75); B. stramineus (9.32); H. marginatus (6.32); P. kennedyi (4.00); and lower in hypogean species, S. typhlops (3.31). All data of this study suggest a strong correlation between swimming performance and the hydraulic environment in which the species are found. The riverine, generalist and lacustrine species (the troglobiotic being included in the last group) showed a trend toward a decrease in speed.