Acute Toxicity of Cadmium to Benthic Oligochaete Worm, Branchiura sowerbyi Beddard, 1982 and Juvenile Catfish, Clarias batrachus Linnaeus, 1758

The present study was done to determine the toxicity of cadmium to Branchiura sowerbyi and juvenile Clarias batrachus. The 96 h median lethal concentrations (with 95 % confidence limit) of cadmium for B. sowerbyi and juvenile C. batrachus were 15.98 (10.78–20.82) and 29.39 (23.70–33.42) mg/l respectively. It indicates that B. sowerbyi was more susceptible to cadmium toxicity than C. batrachus. A significant relationship (p < 0.05) was recorded between mortality rate and all the exposure times at 15, 25, 30 and 35 mg/l of the toxicant for B. sowerbyi and at 26, 30, 36, 48 and 50 mg/l for C. batrachus. Similarly, significant variation was also observed between mortality rate and all the exposure concentrations at all the exposure times (p < 0.01) for both the worm and fish. Excessive mucous secretion, loss of balance and reduced movement were observed in both the worms and fish at higher concentrations during 72 and 96 h of exposure. With progress of time and increasing concentration fish showed behavioural changes like erratic fin movement, hyperactivity, suffocation and increased surface attachment followed by death. The findings of the work can be used in ecological risk assessment and in the determination of safe disposal level of cadmium. © 2014, Zoological Society, Kolkata, India.