Anatomy of finfish and shellfish

Unit 7 - Nervous system in fishes

7.1. Introduction
As in all vertebrates, the nervous system of fishes is the primary mechanism coordinating body activities, as well as integrating these activities in the appropriate manner with stimuli from the environment.
The central nervous system, the brain, and spinal cord, are the primary integrating mechanisms. The peripheral nervous system, consisting of nerves that connect the brain and spinal cord to various body organs, carries sensory information from special receptor organs such as the eyes, internal ears, nares (sense of smell), taste glands, and others to the integrating centres of the brain and spinal cord. The peripheral nervous system also carries information via different nerve cells from the integrating centres of the brain and spinal cord. This coded information is carried to the various organs and body systems, such as the skeletal muscular system, for appropriate action in response to the original external or internal stimulus. Another branch of the nervous system, the autonomic system, helps to coordinate the activities of many glands and organs and is itself closely connected to the integrating centres of the brain.
The nervous system consists of Brain, Spinal Cord and the nervous to co-ordinate various activities (Peripheral nerves and Autonomic nervous) of the body. Fish brain is an enlarged anterior end of the spinal cord. It 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). Its parts progress linearly from a “forebrain” region (enlarged cerebral hemisphere and the connecting tween brain), through the “Midbrain” with its swellings (the optic lobes) to the “hind brain” (cerebellum and medulla) and continue toward the caudal fin with the spinal card (In embryonic) the forebrain is called “Prosencephalon” the mid brain “mesencephalon” and hind brain – Rhombencephalon, the brain and spinal cord are whitish and soft. (The brain is housed in cranium of the skull). The spinal cord runs length wise of the fish in neural canal of the vertebral column. The cerebral hemisphere (forebrain) and cerebellum are more prominent in sharks and relatives (Chondrichthyes) and bony fishes (Osteichthyes) than in the lampreys and hag fishes (Cyclostomes). The “mid brain” prominent in the cyclostomes is also prominent in the Chondrichthyens. However, that of the higher bony fishes (Actinopterygi) is often very large. The cavities of the brain are continuous with that of the spinal cord.
Being highly complex life forms fish need a brain and a nervous system to control their body's actions. The nervous system of fish, much like ours, is composed of a central co-ordinating brain, a spinal cord and many, many nerves.