Encephalization and brain organization of the fishes of the family Osteoglossidae.

Despite their primitive place in the classification of fishes, Osteoglossids have a high level of encephalization, which can be analyzed by studying their brain organization. The quantitative analysis of their main brain parts shows small relative volumes of the olfactory bulbs, normal importance of the optic tectum (linked to vision) and of the cerebellum (linked to motor abilities). The medulla oblongata shows very large gustatory lobes in Heterotis, due to the special microphagous mode of feeding of this species. The cerebral hemispheres are larger in Arapaima than in other osteoglossids, but the lack of data on the comparative behaviour of these fishes does not allow us to give a reliable explantation of this peculiarity.