Abstract The brain gross morphology of Rhamdia quelen is described and compared with seven species of six genera of Heptapteridae. Interspecific variation in shape, size, and position of brain subdivisions was observed in all examined species. The posterior position of the hypophysis on the hypothalamus and presence of a lateral subdivision on the lobus facialis are shared by all examined heptapterids. Rhamdia quelen and Pimelodella gracilis, currently considered closely related within the family Heptapteridae, exhibit the anterior and posterior area of the telencephalon with equivalent widths, and the lateral line lobe reaching the anterior area of the lobus vagi. Members of the so called Nemuroglanis sub-clade (Cetopsorhamdia iheringi, Heptapterus mustelinus, Imparfinis mirini, and Phenacorhamdia tenebrosa) share the lobus vagi proportional smaller than the lobus facialis; the lateral line lobe reaching the half length of the lobus facialis; the tectum mesencephali in contact with the telencephalon, and thinner anterior area of the telencephalon. The results reveal several features that are phylogenetically informative among the heptapterids examined, and corroborate previous hypotheses based on other non-neural anatomical characters.

A morfologia externa do encéfalo de Pseudopimelodus bufonius é descrita e comparada com seus congêneres. As análises foram feitas no cérebro removido após a eliminação dos ossos do topo da cabeça e secção dos nervos cranianos e cordão espinhal. Nove caracteres morfométricos foram obtidos das principais subdivisões do encéfalo, dos quais em sete ocorreram diferenças significativas entre as espécies. Em todas as espécies examinadas do gênero o corpus cerebelli é a maior estrutura do encéfalo. O comportamento das espécies de Pseudopimelodus ainda é desconhecido, mas em outros teleósteos esta característica é normalmente correlacionada com uma boa coordenação motora. Além disso, as proporções relativas do tectum opticum, eminentia granularis, lobus facialis e lobus vagi podem ser relacionadas a hábitos carnívoros e boa capacidade de selecionar alimentos.

The gross morphology of the brain of the pseudopimelodid Pseudopimelodus bufonius is described and compared with congeners. Observations were made on removed brains after elimination of bones from the top of the skull and severing of the cranial nerves and the spinal cord. Nine morphometric characters associated with the major subdivisions of the brain were identified, seven of which revealed significant differences among the species examined. The corpus cerebelli in all examined species of the genus is the largest structure of the brain. The behavior of the species of Pseudopimelodus is still unknown, but in other teleosts that condition is typically correlated with a higher degree of motor coordination. Relative size proportions of the tectum opticum, eminentia granularis, lobus facialis and lobus vagi, might be related to carnivory and an enhanced capacity for food selection.