Genetic variability of three Pimelodidae species, Pimelodus maculatus, Iheringichthys labrosus, and Pinirampus pirinampu, collected at one site in the Tibagi River, was comparatively analyzed using protein data for six systems which code 15 loci in liver, muscle, and heart. The proportion of polymorphic loci (<img src="http:/img/fbpe/gmb/v21n4/21n4a14.jpg" alt="21n4a14.jpg (768 bytes)" align="middle">) for P. maculatus, I. labrosus, and P. pirinampu was 13.33, 20, and 6.67%, respectively, and mean heterozigosity was 6, 8.3, and 4.3%. The genetic identity value (I) was 0.32 between P. maculatus and I. labrosus, 0.37 between P. maculatus and P. pirinampu, and 0.58 between I. labrosus and P. pirinampu. This value suggests that these two latter species are congeneric. However, morphological characteristics place these species in distinct genera.
