Histomorphology of oesophagus and histochemical characterization of oesophageal mucin of the catfish Heteropneustes fossilis

The structural organization of catfish GIT consist of a short, thick-walled oesophagus connected with Jshaped stomach which terminates into three segmented intestine. The histology of gut wall, particularly oesophagus, reveals four typical layers, namely, serosa, muscularis, submucosa and mucosa. The innermost mucosal epithelium is stratified and is made up of basal cuboidal cells, intermediate columnar mucous cells and superficial flattened cells. The middle layer constitutes the major thickness of mucosal epithelium and the taste buds are absent. The mucopolysaccharides present in oesophageal mucosa stain positive with Alcian Blue (pH 2.5) and Periodic Acid Schiff reagent suggesting the presence of acidic and neutral glycoproteins (GPs) where the latter seems to be predominant. There is complete absence of sulphated GP in the oesophagus which is confirmed by the Methylation and Saponification. The neutral GP may aid in lubrication whereas carboxylated glycoproteins may protect the mucosal lining from the invasion of various pathogen. The absence of sulphated moiety may indicate that the functional necessity of this GP may either be diminished or not required at all.