Patterns and processes of brain diversification within esociform teleosts

The richness of nervous systems represented by extant fishes has not yet been fully determined; the brain morphology of many groups remains undescribed. For this reason we have begun to examine the brains of esociforms, a group representing basal euteleosts, focusing here on three goals: 1) to provide the first general descriptions of the brains of two esociform teleosts, Esox masquinongy (muskellunges) and Esox lucius (northern pikes); 2) to describe the neuronal development of E. masquinongy; and 3) to compare the differences in neuronal features between E. masquinongy and E. lucius with reference to the ontogeny of E. masquinongy. We demonstrate that relative to the brains of E. lucius and other basal euteleosts, the brains of E. masquinongy exhibit several paedomorphic features involving the position and morphology of nuclei present throughout the brain. This heterochronic shift parallels differences in nonneural morphological features described between these two species. We conclude that at finer taxonomic levels in some groups such as esocids, aspects of neuronal diversification may be explained by evolutionary transformations involving all body systems. © 1996 Wiley-Liss, Inc.