Physiology of Finfish and Shellfish (2+1)

3.3.1. Introduction

The nervous system of fishes is poorly developed, compared to that of other vertebrates. A bony fish's brain is divided into three sections: the forebrain, the midbrain, and the hindbrain. The forebrain is responsible for the bony fish's ability to smell. Bony fishes that have an especially good sense of smell. Eels, have an enlarged forebrain. The midbrain processes vision, learning and motor responses. Blind bony fishes, such as blind cave fishes in the family Amblyopsidae, have a reduced midbrain. The hindbrain (medulla oblongata and cerebellum) coordinates movement, muscle tone, and balance. Fast-swimming bony fishes usually have an enlarged hindbrain.

The brain of the fish is divided into several anatomical and functional parts, all closely interconnected, but each serving as the primary centre of integrating particular kinds of responses and activities. Several of these centres or parts are primarily associated with one type of sensory perception such as sight, hearing, or smell (olfaction).

The sense organs receive physical or chemical stimuli from the environment. Physical changes in heat flow or touch are felt through skin receptors. Visual stimuli involve changes in light intensity and quality and acoustical ones are received through the inner ear or lateral line. Chemical stimuli are those experienced through either smell or taste organs.