Behavioural and hematological effects of zinc on African catfish, Clarias gariepinus

Ololade I. A.^1* and Ogini O²

¹Department of Chemistry and Industrial Chemistry, Adekunle Ajasin University, P. M. B., 001, Akungba-Akoko, Ondo-State, Nigeria.

²Department of Environmental Biology and Fisheries, Adekunle Ajasin University, P. M. B., 001, Akungba-Akoko, Ondo-State, Nigeria.

*Corresponding author. E-mail: olisa200@yahoo.com. Tel.:+234 8077812009.

Accepted 3 July, 2009

   Abstract

Laboratory investigations were carried out on toxic stress and changes in Clarias gariepinus’ blood cells after a 96-h exposure to zinc. The renewal technique was followed using different concentrations in the range of 30 mg/l to 50 mg/l after a preliminary screening exercise. During the treatment, the color of the experimental fish became progressively darker with increasing concentrations and mortality was directly proportional to the concentrations of the tests solution unlike those in the control. The 96-h median lethal concentration (96-h LC₅₀) was 36.7 mg Zn/l using the logarithmic method. The data obtained showed that the exposure duration evidently influenced the value of median acutely lethal concentration (LC₅₀).The erythrocyte, leucocytes, hematocrit, platelets and hemoglobin count of healthy control indicated a mean value of 3.2 ± 1.2 cells x10⁷ μl, 8.5 ± 3.6 x 10³ mm³, 40 ± 4% , 2.04 ± 1.10 cells x10⁵/μl and 2.06 ± 1.03 x10² g/dl respectively. Apart from platelets, other parameters displayed significant reduction with increased concentration of toxicant in the experimental treatment. The results indicate that Zn is toxic at high concentration producing dose-responsive increases in mortality and abnormalities in behavior. The fish species is therefore recommended as good bioindicator for the risk assessment of aquatic environment due to zinc.

Key words: Zinc, acute toxicity, LC₅₀, behavioral changes, hematology, aquatic toxicity, Clarias gariepinus.