Gross functional anatomy: Integumentary system: Chapter 5

The integument or skin of a fish is the envelope for the body that separates and protects the animal from its environment, but it also provides the means through which most of the contacts with the outer world are made. The integument is continuous with the lining of all the body openings, and also covers the fins. The skin of a fish is a multifunctional organ, and may serve important roles in protection, communication, sensory perception, locomotion, respiration, ion regulation, excretion, and thermal regulation. The most obvious functions of fish integument are protective. For example, mucous secretions help to keep the skin surface free of pathogens by means of constant sloughing and renewal and the presence of antimicrobial substances. Integumentary features can assist a fish during locomotion. The slippery mucus of some fishes has marked friction-reducing properties that enable a fish to move at greater speed with less expenditure of energy. The integument is an important adjunct to the breathing equipment of some fish species. Gas exchange across the skin is known to play a significant role in the respiration of larval fish.