Morphological investigation and functional aspect of the skin of the snout region in koi fish (Cyprinus carpio)

Fish's skin serves a variety of functions that are essential for survival, including communication, respiration, sensory perception, excretion, ion regulation, and heat regulation. This research aimed to examine the snout skin of koi fish (Cyprinus carpio) to determine its structural characteristics. Using light microscopy, the histochemical elements of the skin were examined in a total of 20 adult, healthy koi fish. The skin of was made up of three layers: epidermis, dermis, and hypodermis. The epidermis consisted of epidermal cells, club cells, mucous goblet cells, rodlet cells, eosinophilic granular cells, serous goblet cells, and melanocytes. large amounts mucous of cells which reacted positive to Alcian blue (AB) and Periodic Acid–Schiff (PAS), few club cells which reacted positive to bromophenol blue and light green. many eosinophilic granular cells (EGCs) reacted positive to PAS and light green. Moreover, many taste buds also were demonstrated. The dermis was consisted of collagenous bundles, bundles of myelinated nerve fibers, blood vessels and immune cells. Many telocytes were detected in dermis in close relation to nerve fibers, blood vessels and immune cells. The lateral line system was well-developed in koi fish, where it was arranged into mechanoreceptive superficial and canal neuromasts and electroreceptive tuberous and ampullary organs. In conclusion, the epidermis of snout region in Koi fish consisted of a variety of cells with diverse functions.