A sudden increase in mortality was observed in a fish pond stocked with 1034 6-weeks old Clarias juveniles, after exhibiting various forms of nervous disorders such as severe irritation and erratic convulsive swimming habits. A total of 165 mortality, with mean of 20.6 ± 14.8/day were recorded within the first week of stocking. A perfect positive correlation of water level in the pond R2= 0.92, with inverse mortality R2= 0.14 and pH values R2= 0.78 within the first 8 days were recorded. Carcasses exhibited various forms of skin discoloration, petechial and ecchymotic hemorrhages were observed on the cranium, base of the fins, body sides and bloated belly. Many carcasses had eroded body mucous, manifested by various forms of grayish bands of skin lesion. Mean optimal values for nitrate (0,mg/litre), nitrite (0.1,mg/litre) and ammonia (0.1mg/litre) in the water were recorded using commercial multiple water testing kit, although declining pH value of 11 to 7.5 was observed within the period. Another set of 200 Clarias juveniles of the same batch was raised in an adjacent pond, and appeared clinically healthy. Spontaneous recovery was observed upon transfer of the whole juveniles to a new pond of fresh water, with mean pH 7.5 and treated with oxytetracycline and vitamin-mineral supplements. Diagnosis of acute lime toxicity was made. Normal growth was restored but, evidence of necrotic skin discoloration was retained to adulthood in 20% of the fishes.
Key words: Clarias gariepinus juveniles, hydrated lime, toxicity
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