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.

[Quantitative analysis of the teleost brain: evolutionary and adaptive characteristics of encephalization. III. Multivariate analysis of the cephalic index].

A multivariate analysis of 9 brain indices from 83 teleost species showed a marked opposition between the non-olfactory telencephalon (and diencephalon) and the medulla oblongata (phylogenetic characters) and between the olfactory bulbs and the optic tectum (adaptive characters). Results of three different classifying algorithms allowed determination of 6 stable groupings and 9 intermediate ones, some with systematic importance and some purely adaptive. For this reason brain organization criteria must be used with precaution for systematic purposes.

[Quantitative analysis of the teleost brain: evolution and adaptation. 1. A comparative interspecies study].

The intraspecific brain-body weight allometric coefficient, although high in Teleosts (0.49), is different enough from the interspecific one (0.65, almost 2/3) to use only adult specimens for quantitative studies.

[Quantitative analysis of the teleost brain: evolutionary and adaptive features of encephalization. II. Primary brain subdivisions].

1. Frequently there is an opposition between olfactory and visual senses. Fresh water fishes are generally macrosomatic and microptic, marine fishes (especially coral reef fishes) are microsmatic and macroptic while piscivorous pelagic fishes are macrosmatic and macroptic.