In order to evaluate the efficiency and selectivity of the mechanism transposition of fish from a PCH, 4 collecting expeditions were performed. The collection was made in a period of 24 hours until the end of a Piracema, January 31, 2008. It was collected a total of 3017 specimens, representing 18 species, which 6 belongs to families and 3 to orders. The most abundant species were Pimelodus absconditus (Azpelicueta, 1995) and Schizodon nasutus (Kner, 1858), resulting in a percentage of 48.36 and 26.95 respectively. Hence, the analysis was made regarding sex and stage of maturation of individuals of these species. From the P. absconditus specie, 66 females were collected in stages B (36.67%), and 99 males in stages A (1.11%), B (53.89%) and 15 were immature individuals (8.33%). Already in S. nasutus, 27 females were found in stages A (7.59%), B (18.99%), C (7.59%) and 52 males in stages B (56.96%), C (3.80%) and D (5.06%). It was concluded that the ladder is selective, which shows that only species of small size can rise it, because most of the individuals were at maturation stage.