Histopathological analysis of the respiratory organs of Channa striata subjected to air exposure

Effects of air exposure on the respiratory organs of Channa striata possessing bimodal respiration for exploitation of water (via gills and skin) as well as air (through air breathing organs suprabranchial chamber, ABOs) have been investigated. On air exposure the fish survived for 8 h. Following air exposure the fine, thin-walled blood capillaries (BLCs) at the surface of the ABO swelled and bulged out due to congestion when the blood came very close to air in the lumen. In the initial periods, mucous cells (MCs) of all three respiratory organs showed periodic fluctuations in their density and staining properties and stain for sulphated moieties known to hold an additional quantity of water. The sub-epithelial connective tissues of the ABO and skin also contained a large quantity of sulphated mucopolysaccharides. Subsequently, severe wear and tear and sloughing leading to haemorrhage took place from the skin. The outer cellular layers of the epidermis sloughed off. The density of sacciform-granulated cells (SGCs) increased and stained strongly with PAS technique (almost negative in controls). Air exposure also caused extensive damage in the gills. In the initial periods the BLCs showed severe congestion, causing extensive bulging and protrusion onto the surface. Later, the epithelial linings of gill filaments (PL) as well as respiratory lamellae (SL) were detached and lifted up. Subsequently, the neighbouring SL fused, causing decreased surface area, thereby reducing the efficiency of gills. The ladder-like arrangements of the pillar cells blood capillaries (PLCs-BLCs) also collapsed. PAS-positive materials appeared within these PLCs. Subsequently, the BLCs dilated and showed congestion. The RBCs of gills also showed PAS staining. A thin layer of sulphated slime often covered the respiratory epithelia. Prior to death of the fish, the cells of the gills degenerated extensively. Thus, air exposure also prevented normal branchial respiration and the fish died due to anoxia and other physiological disorders.