A histochemical study on the respiratory epithelium of an eel fish - Amphipnous cuchia (Ham)

The respiratory epithelium of the air sac and that of the buccal cavity resemble each other in having high vascularization, very small air/blood pathway (below 1 mum), phospholipid, ascorbic acid content and having two morphologically distinct mucous cells. The larger mucous cells appear to secrete strongly acidic sulfated mucopolysaccharides while the smaller ones are responsible for secreting sialic acid containing glycoproteins. Elongated mucous cells with foamy cytoplasm and tapering apex of the vascularised buccal epithelium are similar in histochemical properties to the same type of mucous cells reported in the epidermis of the skin. These cells secrete weakly acid mucopolysaccharides. Negligible number of mucous cells are present along the margin of the fused gill filaments of the gill. Presence of large amount of scattered phospholipid globules in the respiratory epithelium appears to be true of all the air breathing fishes utilising oxygen from air. Foreceful water or air breathing for nearly 5 1/2 h by the fish does not indicate change of phospholipid content of the respiratory epithelium but prevention of surfacing a continuous flow of water system resulted in 35% increase in blood ascorbic acid and more concentration of vitamin C granules along the respiratory epithelium.