Ecology of Pimelodus maculatus (Siluriformes) in the Corumbá Reservoir, Brazil

Pimelodus maculatus, were studied in different environments of the Corumby Reservoir and its main tributaries in Goias 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 22.0cm 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.Original Abstract: Pimelodus maculatus, ont ete etudiees dans differents biotopes du reservoir de Corumba et dans ses principaux affluents dans l'Etat de Goibas, Bresil. Les echantillonnages ont ete realises mensuellement, de mars 1998 a fevrier 1999, en utilisant des filets maillants et des palangres. L'espece presente une large distribution et a ete capturee dans toutes les stations d'echantillonnage. Dans les peches au filet maillant, un grand nombre d'individus a ete recolte a la station Jacuba du reservoir et cette espece a represente la plus grande biomasse a la station en aval du reservoir de Corumba. La premiere maturite sexuelle est atteinte a la longueur standard de 15,6 cm pour les males et de 17,8 cm pour les femelles. La totalite des individus etait adulte a 18,0 et 22,0 cm, respectivement pour les males et les femelles. La population etait composee d'une forte proportion de jeunes individus dans tous les sites. La periode de reproduction, de novembre a janvier, est liee a un pH legerement acide, a de longues photoperiodes, a de hautes temperatures et a de hautes concentrations d'oxygene dissous. La reproduction a ete observee dans les stations d'eau courante en aval et en amont du reservoir, au-dela de la riviere du Peixe, ce qui indique que les individus realisent des migrations de faible amplitude afin de se reproduire.