Behavioural surveillance of Indian major carp Cirrhinus mrigala (Hamilton) exposed to free cyanide

The toxicity of free cyanide (i.e. sodium cyanide) to the freshwater fish Cirrhinus mrigala was studied using static bioassay method. The LC50 in 96 h was found to be 35 μg/L. Behavioural changes when exposed to lethal concentration of free cyanide showed increased opercular movement, increased surface behaviour, loss of equilibrium, change in body colour, increased secretion of mucus, irregular swimming activity, rapid jerk movement, ‘S’ jerk, partial jerk and aggressiveness.