RESUMO
The encephalon gross morphology of Geophagus sveni is described, compared between male and female specimens and discussed in relation to evolutionary, ecological and behavioural aspects. The Student's t-test revealed that there are no sexual dimorphism regarding the volume or linear measurements obtained from the main encephalon subdivisions (telencephalon, tectum mesencephali, cerebellum, gustative lobes, hypothalamus and hypophysis) in proportion to encephalon length, which is congruent with the absence of external dimorphic characters and presence of biparental care behaviour. In all specimens examined, the tectum mesencephali is the largest structure of the encephalon, which may be explained by feeding habit and by the importance of the vision center in a social context (i.e., brood guarding and territory defence, which are common behaviours in cichlids). Also, the lobus vagi is more developed than usual for other teleosts, which may be explained by the presence, in G. sveni as well as in other Geophagini species, of a differentiated pharyngeal apparatus, probably an adaptation to winnowing, a specialized feeding habit. The little intraspecific variation in neuroanatomical characters observed herein indicates a possible source of morphological characters to be explored in cichlid phylogeny.
