Keratinization and mucogenesis in the epidermis of an angler catfish Chaca chaca (Siluriformes, Chacidae): A Histochemical and fluorescence microscope investigation.

The present study describes keratinization and mucogenesis in the epidermis of an angler catfish Chaca chaca, using a series of immunochemical, fluorescence and histochemical methods. The epidermis is primarily mucogenic and shows characteristic specialised structures at irregular intervals. These structures are identified keratinized in nature. The superficial layer epithelial cells in the keratinized structures often detach from the underlying epithelial cells and exfoliate either singly or in the form of sheet. This is associated to provide protection by removing silty depositions, pathogens, and debris along with exfoliated keratinized cells/sheets periodically to keep the skin surface clean. Mucogenic epidermis is equipped with the mucous goblet cells and the club cells. Nevertheless, these cells are not discernible in the keratinized structures. This suggests an inverse relationship between mucogenesis and keratinization in the epidermis of the fish. The mucogenic epidermis is involved in the secretion of different classes of glycoproteins. These include glycoproteins with oxidizable vicinal diols, glycoproteins with O-sulphate esters and glycoproteins with sialic acid residues without O-acyl substitution. Secretion of these glycoproteins on the surface are associated to control the acidity of the acidic glycoproteins, to protect the skin surface against bacterial, viral infection and other pathogens, and help in lubrication to protect against abrasion during burrowing. Epidermal keratinization and glycoprotein characterization are associated with the physiological adaptations in relation to the characteristic habit and habitat of the fish.