BRAIN AND NERVOUS SYSTEM | Functional Morphology of the Brains of Ray-Finned Fishes

Abstract

Ray-finned (actinopterygian) fish are an extremely diverse radiation, as reflected in the wide range of variation in the development and structure of various parts of their brains. Variation in the numbers of neurons that are generated by the germinal zone, which lies along the ventricular surface, and variation in the degree to which the neuron cell bodies migrate away from that zone results in marked differences in brain structure and organization. Many structures in the hindbrain, midbrain, and forebrain of ray-finned fish are similar across this taxon and also regarding those in the other major groups of vertebrates, including many of the cranial nerve nuclei and the various sensory and motor system pathways. Specializations in the hindbrain include marked hypertrophy of some of the sensory regions, including the regions involved in the gustatory system in cyprinids and catfish and the cerebellum and its related structures in electroreceptive ray-finned fish, such as mormyrids. In the midbrain, specializations include those of the oculomotor nucleus and the extraocular muscles they innervate for generation of electric impulses in the stargazer, and some pretectal specializations occur in relation to feeding behaviors in some species. The eversion process that the telencephalon undergoes during development in ray-finned fish makes comparison with other major vertebrate groups difficult, but some sensory system inputs appear comparable, and some of the functional capabilities are surprisingly like other vertebrates, including mammals.