AN ELECTRON MICROSCOPIC STUDY OF THE RESPIRATORY EPITHELIUM IN THE AIR RESPIRATION ORGANS OF CLARIAS FUSCUS,CHANNA ASIATICA AND MISGURNUS ANGUILLICAUDATUS

The structure of the air respiratory organs of the fishes,Clarias fuscus with arborescent organs,Channa asiatica with ear-shaped labyrinthine organs and Misgurnus anguillicaudatus with air respiratory intestines has been investigated by scanning and transmission electron microscopy. The resuli suggests that the air respiratory organs are covered by a highly vascularized respiratory epithelium on the surface in all three freshwater species.In C. fuscus,the surface of the respiratory epithelium is corn like. The semicircle cobblestone-shaped protrusions are present on the surface of the labyrinthe organs in C. asiatica. M. anguillicaudatus has a cloud-shaped surface in its inner wall of the intestines. All respiratory epithelial cells of three air respiratory organs are the same type which is a kind of modified squamous epitheial cells. ,They show the ultrastrural characteristics of both type Ⅰ and type Ⅱ epithelial cells of lung alveoli in mammals. At the same time,the blood-air barrier is composed of three layers:the thin layer of the extended cytoplasm of respiratory epithelial cells,the thin sheet of cytoplasm of endothelial cells and the basement membrance between them is similar to that of the respiratory organs in other vertebrates.