Anatomy of finfish and shellfish

Unit 11 - Sensory System in fishes

11.4. Skin organs
Numerous microscopically small opening of skin sensory organs are developed on the surface of the fish body. In most fishes a series of these pores, extending along each side in a single row from the head to the caudal fin comprises the lateral line. The lateral line system forms branches about the head, including one above and one below the orbit of each eye. In some fishes like Pikes, Esox lucius and Silver sides, the pores and their sensory organs are not linearly concentrated on the body but are rather widely scattered. In sharks and their relatives, there are extra and specialized parts of the lateral line system, especially in the snout region. In few fishes taste buds occur in the skin and intigumentary tactile sensory structures.
A catfish uses taste and touch when examining a food object with its oral barbels. Like most other animals, fishes have many touch receptors over their body surface. Pain and temperature receptors also are present in fishes and presumably produce the same kind of information to a fish as to humans. Fishes react in a negative fashion to stimuli that would be painful to human beings, suggesting that they feel a sensation of pain.
An important sensory system in fishes that is absent in other vertebrates (except some amphibians) is the lateral line system. This consists of a series of heavily innervated small canals located in the skin and bone around the eyes, along the lower jaw, over the head and down the midside of the body where it is associated with the scales. Intermittently along these canals are located tiny sensory organs (pit organs) that apparently detect changes in pressure. The system allows a fish to sense changes in water currents and pressure, thereby helping the fish to orient itself to the various changes that occur in the physical environment.