ABSTRACT. Dis tribution and relative abu ndance of the catfish Trachelyopterus striatulus Steindachner (Osteichthyes, Auchenipteridac) in the Lajes Reservoir, Rio de Janeiro, Brazil. The catfish Tra che/yopterus striatu[us Steindachner, 1877 is a very ab undant fi sh species in reservoirs in Southeast Brazil , and its re lati ve abu ndance seems to be increasing in severallentic environments. Despile of being a very common species, few info rmation is avai lable on ils di stribution and other aspects of ecology. The Lajes reservoir (22°42' -22°50'S e43°53 ' -44°05 ' W) is the largest manmade lake forhydropowe r purposes in Rio deJ aneiro Slate, where Ihi s specie rank arnong the top abundant fi shes, bot h in number and in biomass. lts re lati ve abundance were compared in three zones of the reservoir (upper, centra l and lower), based on a standardi zed program , during three annual periods (monthl y sampling in 1994 and bi-monthly sampli ng in 1996 and 1997), with a total of three hundred twenty samples, using gi ll nets. Environmental variables of water temperature, pH and lransparency were taken in each sampling occasion, and information on rainfall and leve i of lhe water were recorded. Trachelyopterus striatulus showed an increasing abundance during lhe study pe riod, risi ng from fifty rank in 1994 to the most ab undanl fi sh in 1997, coinciding with decreasing waler levei, and suggesling lhat lhi s species take advantage of the harsh condi tions in the reservoi r to increase population. Hi ghesl number and weighl were recorded in lhe upper zone, which presented lhe lowest tran sparency. Seaso nally no significance (p > 0,05) differen ce in abundance was fo und over the whole peri od. KEY WORDS. Auchenipteridae, distri bution, abundance, environmental pararneters, Lajes, reservoir Membros da família Auchenipteridae, conhecidos como cangatis ou cumbacas, encontram-se distribuídos em rios e represas de toda a América do Sul tropical estendendo-se desde o Panamá até a Argentina ( NELSON 1976). Esta família é representada no reservatório de Laj es por uma única espécie, T. striatulus Steindachner, 1877, e pouco é conhec ida sobre sua distribuição e abundância, apesar de suas elevada ocorrência.
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