Gross variations in relative size of brain and its subdivisions among fishes: An overview

Abstract

Fishes are the aquatic vertebrates inhabiting all the levels of the water column. Different species of fishes are well adapted to successfully live in all types of water bodies. They possess a well-developed nervous system to combat all the challenges they encounter in their specified habitat in the water column. Fishes that are migratory in nature are also able to overcome the problems faced by them in moving from one type of water body to the other. Although the sub divisions of the brain in different species of fish are same, there occurs a considerable variation among them owing to the whole brain size, shape and size of sub divisions etc. Studies have reported variations in whole brain size and enlargement of a particular brain subdivision that may be correlated with the body size, ecological niche or habitat of the species or cognitive ability of the species. Most of the studies performed with this objective reported interspecific variations among fishes. Fewer studies however, reported intraspecific morphological variations in brain/brain subdivisions among the fish population. Nevertheless, brains are energetically costly organs. Super class Pisces including all the fishes is a diverse group with respect to body size and habitat within water column and all such studies are so scattered that it is difficult to summarize them all. Therefore, the aim of this paper is to discuss and provide information about the variations in the brain size and in its subdivisions and unique brain structures found in fishes. Such studies were conducted in earlier times also and are gaining a great interest since past 10 years.