Author(s): Gautam Das, Nabajyoti Das and Dr. Parag Deka

Abstract: The present investigation deals with the toxicological effect of mercuric chloride on a model fish organism Heteropneustes fossilis on haematological parameters as well as behavioural changes keeping most of the physicochemical parameters in the experimental aquariums are at optimal level. The LC₅₀ concentration where 50% death of the fishes occur is experimentally carried out which is found to be 0.10 mg/l, a very lesser quantity, thus showing the level of toxicity of mercuric chloride. The fishes were treated at sub lethal concentration of LC₅₀ (1/5^th of LC₅₀ concentration i.e. 0.02 mg/l) for a period of 24hrs, 48hrs, 72hrs and 96hrs to get haematological alteration. The result shows that RBC and Haemoglobin decline significantly as the increase of time of exposure of mercuric chloride. Haemoglobin % was observed to drop about 50% after 96 hours of exposure of mercuric chloride. However, WBC is found to be increased with time initially and attain maximum at 48 hours of exposure and steadily decline thereafter. Differential Leucocytes Count (DLC) shows an increasing trend as the exposure of mercuric chloride increases. Lymphocytes shows an increasing trend from lower to higher as exposure time increases with more or less similar trend with Basophil, where the highest peak is observed at 48 hours exposure time and then decline slowly. On the other hand Eosinophil, Neutrophil and Monocytes show a reverse phenomenon where the number of counts decreases steadily as exposure time increases. The various behavioral changes like restlessness, abnormal swimming behavior, vigorous jerks of body, loss of balance, surfacing, encircling, mucus secretion and anorexia observed in Heteropneustes fossilis indicates the effect of the level of toxicity of mercuric chloride.

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