
In this present study, the mortality rate of heavy metal lead nitrate (Pb(NO3)2) was determined in the freshwater fish Catla Catla. The median lethal concentration was determined using static and renewable method through Probit analysis. The median lethal concentration (LC50) value of (Pb(NO3)2) was found to be 190.56, 181.81, 172.43 and 163.04 mgL-1 for 24, 48, 72 and 96 hrs respectively. The dose and time dependant responses (mortality rate and behavioural changes) in the test fish was observed. The behavioural changes observed in the experiment includes hyper activity, loss of balance, vertical and downward swimming pattern, frequent surfacing activity, convulsion, difficulty in breathing and mucus secretion over the body. No behavioural changes or death were observed in the control group during the experiment. The results of the study showed that, acute lead toxicity severely affects the normal behaviour and results in death.