Abstract
Rhyacichthys aspro has one of the highest encephalization indices of the Gobioidei, at the level of the amphibious Periophthalmus (Gobiidae, Oxudercinae). This high encephalization can be explained by its adaptation to the turbulent waters of mountain torrents. The brain morphology is typical of a perciform fish and similar to that of a gobioid except in the form and size of the cerebellum. The quantitative analysis of the brain structures shows a large size of the olfactory centers, a small size of the visual centers (compared to those of other Gobioidei) and a very large size of the cerebellar centers (more than twice the size in other Gobioidei). The brain organization shows that Rhyacichthys aspro, although some of its brain structures are typically gobioid (tegmentum, medulla oblongata), is not a generalized gobioid, because of the high degree of its biological adaptation and the correlated large size of its cerebellum.
