Population structure of Rhamdia hilarii Valenciennes, 1840 (Osteichthyes, Siluriformes, Pimelodidae

Abstract

In order to know some aspects of biology and autoecology of Rhamdia hilarii (Valenciennes, 1840) of Jaguari River (Jaguariúna, SP), the data and material of 1490 fishes collected from July 1973 through June 1975 were analyzed. Chi-square tests indicated a significant difference from the expected 1:1 sex-ratio for total individuals. The sex-ratio varied from one year to another. Females predominated in the first cycle and males, in the second. The length composition of population for each period and during the year was analyzed. The females were larger than the males. The males matured shortly before the females.