Histochemical analysis of glycoproteins in the gill epithelium of an Indian major carp, Cirrhinus mrigala

Glycoproteins were analyzed by a range of histochemical methods in the epithelium of gills of Cirrhinus mrigala, a valuable food fish of great economic importance cultured extensively in India. The gills consist of gill arches, gill rakers, gill filaments and secondary lamellae. Major components of the epithelium of gill arches and gill rakers are epithelial cells, mucous goblet cells, rodlet cells, lymphocytes, eosinophilic granular cells and taste buds. In contrast, in the gill filament epithelium, rodlet cells and taste buds, and in secondary lamellae epithelium, rodlet cells, lymphocytes, eosinophilic granular cells and taste buds are not discernible. The epithelial cells, the mucous goblet cells and the eosinophilic granular cells elaborate glycoproteins with oxidizable vicinal diols and glycoproteins with sialic acid residues without O-acyl substitution. In addition, glycoproteins with O-sulphate esters are secreted by the mucous goblet cells. The rodlet cells elaborate glycoproteins with oxidizable vicinal diols. Different types of glycoproteins elaborated on the epithelial surface of gills are discussed in relation to physiological significance of glycoprotein classes with special reference to their roles in lubrication, protection and inhibition of invasion and proliferation of pathogenic micro-organisms.