RESUMO
Sublethal cadmium chloride [0.3 ppm] toxicity induced stress related morphopathological alterations in the accessory respiratory organ of the air-breathing catfish Heteropneustes fossilis [Siluriformes; Heteropneustidae] have been investigated at various intervals of exposure. The histopathological manifestation of the cadmium toxicity includes bulging of the hyperemic secondary lamellae into the lumen of the accessory respiratory organ, necrosis and sloughing of the respiratory epithelium leading to haemorrhage and fusion of SL at various stages of the exposure. Periodic alterations in the densities of epithelial cells and mucous cells along with the development of non-tissue spaces have also been noticed at different exposure periods leading to alterations in the thickness of the respiratory epithelia. The heavy metal salt exposure has affected the mucogenic activity of the respiratory epithelium not only quantitatively but qualitatively also, indicating the probable ameliorative role fish mucus in cadmium toxicity