Abstract
The rivers that are potential breeding grounds of Cirrhina mrigala are subject to heavy metals pollution through industrial effluents and domestic sewage. In present investigation, laboratory experiments were conducted to study the acute toxicity of metals viz. iron, zinc, lead, nickel and manganese on the three age groups viz. 30-, 60- and 90-day of Cirrhina mrigala. Data obtained from the acute toxicity tests were evaluated by using the Probit Analysis Statistical Method. The study includes the determination of 96-hr LCso and lethal toxicity to the fish. The tests were performed, separately, at constant temperature (30 DC), pH (7) and hardness (100 mql,") of water. Physico-chemical variables viz. dissolved oxygen, total ammonia, sodium, potassium and carbondioxide were also studied during the experiment. The 96-hr LCso and lethal concentrations of all metals varied significantly in fish. This fish showed significantly highest sensitivity (determined LCso as 29.55 ± 5.39 mg L-1 ) against nickel, followed by that of lead (39.51 ± 5.84 mg L-\ zinc (48.41 ± 6.79 mg L-\ manganese (79.97 ± 8.48 mg L-1 ) and iron (86.24 ± 16.87 mg L-\ The responses of three fish age groups in terms of LCso and lethal concentrations were statistically significant also. Among the three fish age groups, 90-day fish showed significantly higher tolerance against all metals than that of 60- and 30-day fish. The ammonia excretion by the fish increased significantly with increase in metals concentrations of the mediums. However, carbondioxide contents of the test medium increased at higher metals concentrations. Key words: Cirrhina mrigala, 96-hr LCso, lethal, iron, zinc, lead, nickel, manganese
