The catfish Trachelyopterus striatulus Steindachner, 1877 is a very abundant fish species in reservoirs in Southeast Brazil, and its relative abundance seems to be increasing in several lentic environments. Despite of being a very common species, few information is available on its distribution and other aspects of ecology. The Lajes reservoir (22º42'-22º50'S e 43º53'-44º05'W) is the largest manmade lake for hydropower purposes in Rio de Janeiro State, where this species rank among the top abundant fishes, both in number and in biomass. Its relative abundance were compared in three zones of the reservoir (upper, central and lower), based on a standardized program, during three annual periods (monthly sampling in 1994 and bi-monthly sampling in 1996 and 1997), with a total of three hundred twenty samples, using gill nets. Environmental variables of water temperature, pH and transparency were taken in each sampling occasion, and information on rainfall and level of the water were recorded. Trachelyopterus striatulus showed an increasing abundance during the study period, rising from fifty rank in 1994 to the most abundant fish in 1997, coinciding with decreasing water level, and suggesting that this species take advantage of the harsh conditions in the reservoir to increase population. Highest number and weight were recorded in the upper zone, which presented the lowest transparency. Seasonally no significance (p > 0,05) difference in abundance was found over the whole period.
Auchenipteridae; distribution; abundance; environmental parameters; Lajes; reservoir