Histochemistry and the structure of the skin of a murrel, Channa striata (Bloch, 1797) (Channiformes, Channidae). I. Epidermis.

Abstract

The functional organization and cytochemistry of the epidermis of an air-breathing fish, Channa striata, is described. In the basal cells a dense population of mitochondria, strong alkaline phosphatase, and succinic dehydrogenase activity indicates high metabolic activity. In the outermost layer, polygonal cells showed strong succinic dehydrogenase activity and elaborated sulfated acid mucopolysaccharides and lipids. Mucous cells were also numerous. A new term, 'sacciform granulated cells,' is proposed for the 'sacciform cells' or 'granular cells.' The contents of these cells are basic proteins. A thick coat of slime containing mucopolysaccharides, lipids, and basic proteins is probably important in keeping the skin moist for cutaneous respiration, retarding the rate of water loss by evaporation, facilitating burrowing in the mud and swimming movement in water, and protecting the skin from bacterial and fungal attacks. A relatively thin epidermis (32 μm on the general surface, 18 μm at the posterior free margins, and 6 μm below the scales) in conjunction with vascularization of the stratum laxum probably assists cutaneous respiration.