Pathology of gas bubble disease in two air-breathing catfishes (Clarias batrachus Linn. and Heteropneustes fossilis Bloch.)

Gross pathology in Clarias batrachus and Heteropneustes fossilis, and histopathology in the liver, intestine and kidney and abnormalities in erythrocyte count/mm³ and haemoglobin g% of C. batrachus afflicted with gas bubble disease were studied over 96 h. Histopathology and blood abnormalities in H. fossilis could not be observed due to heavy mortality. A tilt in the swimming posture and an upward bend in the tail region were the first signs of the disease. Exophthalmia was noted and blebs containing gas bubbles appeared on the fins and other parts of the body. The blebs burst producing open lesions after 72 h, and the fins became necrotic.Histopathologic changes included, in the liver, vacuolation of cells, necrosis and cordal disarray; in the intestine, lesions in the villi, degeneration of the submucosa, cellular exudate production in the lumen and air bubbles in the villi; and in the kidney, degeneration of tubules and glomeruli and necrosis of haemopoietic tissue. Erythrocyte count and haemoglobin content showed a consistent and significant fall from 12.87 × 10⁶ to 6.91 × 10⁶/mm³ and from 9.33 to 7.00 g%, respectively, up to 72 h. Empty blood vessels were noted in the liver, intestine and kidney. Fish of both species regained normal swimming orientation, and erythrocyte count and haemoglobin content also showed recovery from the disease.