Effect of short-term exposure to mercuric chloride on the air-breathing catfish, Heteropneustes fossilis. II. Scanning electron microscopic study of the gill.

Histopathological effects of sublethal (0.1, 0.2, 0.3 ppm) and lethal (0.5, 1.0 ppm) solutions of mercuric chloride (HgCl2) have been studied on the gills of the air breathing catfish, Heteropneustes fossilis at the intervals ranging from 6h to 15 days. Thickening of the epithelium, swelling and hyperplasia of the mucous cells, fusion of secondary lamellae, formation of interlamellar bridge and deposition of mucous over the entire surface are some noteworthy features of mercury poisoning in sublethal concentrations. Acute pathological manifestations are formation of subepithelial space, sloughing of the epithelial layer, hemorrhage and hypertrophy of the mucous cells. Causes and impact of these cellular alterations affecting survival of the fish have been discussed.