Scanning electron microscopic observations of Basic Violet-1 induced changes in the gill morphology of Labeo rohita

Scanning electron microscopic observations were made for the changes in the surface ultra morphology of gill of Labeo rohita as indicators of the stress of lethal (0.1, 0.2, 0.4, 0.6, and 0.8 mg/L dye) and sublethal (0.0225, 0.045, and 0.09 mg/L dye) doses of Basic Violet-1 (CI: 42535, Trade name- Methyl Violet-2B). Present study was taken up as insufficient data exist regarding safety of this dye. The dye was observed to be cytotoxic in nature during the short term (96 h) exposure to lethal doses and tumorogenic as well as cytotoxic during the long term (150 day) exposure to sublethal doses. The dye caused reduction or complete loss of microridges, proliferation of chloride cells, and degeneration of gill lamellae and rakers. The toxic effects became more pronounced with duration as 0.0225 mg/L dye caused remarkable distortion of the normal structure of gills after 150 days of exposure. Such changes may have become the underlying cause for 45-50 % mortality of fish exposed to even sublethal doses of dye as the gills of fish perform a range of vital functions. In the present study, changes in ultra morphology were observed on the 50th day whereas mortality was noticed between 100 and 150 days of subchronic exposure. Therefore, time to time monitoring of ultra morphology of gill will provide us early indicators for the stress of very low levels of pollutants which may later cause mortality of the fish.