Toxicity of calcium hypochlorite on fingerlings of Clarias gariepinus (Burchell, 1822)

Abstract

The toxicity of calcium hypochlorite (containing 65% chlorine disinfectant) was investigated on fingerlings of Clarias gariepinus. Fish of mean weight of 5.5 ± 0.8g and total length of 7.8 ± 0.5cm were exposed to various concentrations (0.00, 0.011, 0.033, 0055 and 0.077 mg/I) of calcium hypochlorite resulting in residual chlorine of(0.00, 0.002, 0.006, 0.010 and 0.014 mg/l respectively) for 12, 24, 48 and 96h, adopting a static bioassay technique. The water quality, tolerance and behavioural responses, haematological and histopathological parameters of fingerlings of Clarias gariepinus were monitored and measured using standard methods. Blood samples were obtained from the caudal circulation and used for the measurement of Packed Cell Volume (PCV), Haemogolobin level (Hb), Red and white Blood cell count. Erratic swimming, excited competitive movements and gasping for air at the surface were the behavioural changes observed with increase in time of exposure and concentration of the chemical. The water quality parameters were measured during and after the experiment. Significant differences were observed. The PCV showed significant (P<0.05) decrease in values between 25% and 20% in all concentrations compared to the control value of 29% at 96h exposure. Haemoglobin levels were similarly significantly (P<0.05) lowered from the control value of 8.3g/dL to 6.7g/dL in the varying concentrations with increase in time of exposure. Deteriorating changes were observed in the liver, gill and brain of fingerlings of C. gariepinus exposed to calcium hypochlorite with increase in both concentration and time of exposure. It is therefore concluded that treated municipal water supply which usually contains residual chlorine of 0.20ppm is not suitable for aquaculture. It is recommended that the water should be exposed to light between 24 to 48 hours in order to allow for the evaporation of the residual chlorine present in it if it must be used at all. Calcium hypochlorite should not be used indiscriminately in aquaculture systems.