ABSTRACT
The skin of a fish is a multifunctional organ and may serve important roles in communication, sensory perception, locomotion, respiration, excretion, osmoregulation, and thermal regulation. The skin is a self-active secretory organ that their cellular components provide many useful products. Goblet cells secrete mucus that keeps the body surfaces moist and protects it from stressors, while the club cells produce the alarm substances that initiate the alarm reaction. The dermal chromatophore units provide patterns of coloration and absorb or reflect radiations. They include melanophores, xanthophores, erythrophores, and iridophores. The skin of fish shows various inter-species differences, as some species have scales and others have special cells, such as sacciform cells, eosinophilic granular cells, and rodlet cells. The skin is also a vehicle for cutaneous sense organs that allowed the fish for the detection of predators and foods. Among them are taste buds and the lateral line system. The lateral line is a sensory system that allows fish to sense objects and motion in their surrounding aquatic environment. The lateral line system is categorized into two subsystems: mechanoreceptive neuromasts and electroreceptive ampullary and tuberous organs. Two types of neuromasts occurred in fish species: superficial and canal neuromasts (CNs). The tuberous organ is more frequently occurring in the head region and contains four to five sensory receptor cells that play a significant role in the sensation of weak electrical stimuli. CNs are embedded in the dermis in the form of tunnel-like canals. A large number of superficial neuromasts are located at the lower lips and the head of a red-tail shark. The ampullary organ (AO) is localized in the head region behind the eye and is formed of specialized receptors that play important roles in detecting the electromagnetic fields, as well as temperature gradients. AOs have been classified into two different types based on the size and the length of the canals.
100Skin is the structure that covers the body and protects it not only from the entry of pathogens or allergens but also from the leakage of water, solutes, or nutrients. These outside-in and inside-out barrier functions are dependent on the epidermis. The skin of a fish is a multifunctional organ and may serve important roles in communication, sensory perception, locomotion, respiration, excretion, osmoregulation, and thermal regulation. Teleost skin, in particular, is unique and histologically diverse. It is very different from that of mammals because it secretes mucus, which is involved in immune functions. Its structure and function reflect the adaptation of the organism to the physical, chemical, and biological properties of the aquatic environment and the natural history of the organism. The aquatic environment is rich in pathogenic organisms; hence, the skin of aquatic vertebrates is extremely important as the first line of defense against the invasion of environmental pathogens.
The skin is a self-active secretory organ that their cellular components provide many useful products. Goblet cells secrete mucus that keeps the body surfaces moist and protect it from stressors, club cells (CCs) produce the alarm substances that initiate the alarm reaction and melanocytes (MCs) produce pigments to provide the fish with specific colorations. The skin is also a vehicle for cutaneous sense organs allowed the fish for the detection of predators and foods. Among them are taste buds (TBs) and lateral line systems that include neuromasts and electroreceptive organs. The skin of fish shows various interspecies differences, as some species have scales and others have special cells. The skin was composed of the epidermis of nonkeratinized stratified squamous epithelium, followed by dermis of dense regular connective tissue.
