In bioassav experiments with Liza parsia to 'Nuvan’ for acute exposure, the 48 and 96 hr LC50 were found to be 0.750 and 0.482 ppm respectively in a brackishwater medium of salinity 10 ± 1.0%_o, temperature 27.5± 1.5^o C and pH 6.0 ± 0.5. For sub-lethal effects the fishes were exposed to l/5^th and 1/5^th concentrations of this 96 hr LC50 value for 45 days. In histological investigations of liver and kidney of the fishes from both these acute and sub-lethal exposures, disorders such as vacuolation. Extensive coagulative necrosis with pyknosis. Karyolysis in liver tissue and enlargement of renal tubules, necrosis of epithelial tubular cells in kidney were observed. Safe levels for long-term use are yet to be found out.