Effect of cadmium chloride on general body colouration and chromatophores of stinging cat fish, Heteropneustes fossilis (Bloch)

Chromatophores, specialized pigment cells in poikilothermic animals, have shown great potential in their use as a cell-based biosensor in the detection of a broad range of environmental toxicants, as structure and number of chromatophores alters significantly under toxicant exposure. Skin coloration of Heteropneustes fossilis is due to melanin containing melanophores. Cadmium, the black listed and non essential heavy metal, is widely used that adversely affects vital activities of aquatic biota. H. fossilis, freshwater Indian stinging catfish, were subjected to exposure of 96 hour LC50 dose (392.92 mg/l) and 25% of 96 hour LC50 dose (98.23mg/l) of cadmium chloride (CdCl2) to evaluate toxic impact of cadmium on colouration and chromatophores. A significant decrease was observed in number of chromatophores after acute (highly significant (F = 70.50; P<0.001) and sub acute (significant (F = 0.29; P<0.05) exposure along with heavy nacrotic, lytic and degenerative changes. Chromatophore gradually changed from reticulate to punctate-stellate and punctuate type as they lost their dendritic processes and aggregation of melanin towards centre. Most of the chromatophores lost their cellular entity due to degenerative changes and melanin was found dispersed in surrounding matrix. Peeling and fading of skin was the common feature in all exposure durations. Fish chromatophores may serve as better biomarkers in reference to metallic pollution and will also be helpful in accessing the health status of economically important fishes as well as worsening status of aquatic bodies.