The distribution, abundance and reproduction of the “mandi”, Pimelodus maculatus, were studied in different environments of the Corumbá Reservoir and its main tributaries in Goiás State, Brazil. Samplings were carried out monthly from March 1998 to February 1999, using gillnets and longlines. The species was widely distributed, being caught at every sampling site. In gillnet samples, P. maculatus had high frequency at the Jacuba Reservoir site and high biomass at the site downstream from the dam. Juveniles had high frequency in every environment. Average size at first maturation was 15.6 cm standard length for males and 17.8 cm for females. All individuals were adults at 18.0 and 22.0 cm for males and females, respectively. The reproduction period (November to January) was related to the slightly acid pH, long photoperiod and high temperature and concentration of dissolved oxygen. Reproduction was documented in running water, downstream from the dam, upstream from the reservoir and in the Peixe River, the latter suggesting short migrations to reproduce.