Subchronic toxicity effects of the residual levels of chlorpyrifos on cytochrome P450 induction, selected hematological and histological parameters of Nile tilapia (Oreochromis niloticus Linn.)
2000
Aragon, M.G.R.
This study aimed to determine the subchronic toxicity effects on the hepatic cytochrome P450 levels, various blood parameters and histology of selected organs of Nile tilapia (Oreochromis niloticus Linn.) following exposure to the detected residual level in rice paddies of the insecticide chlorpyrifos. Weight gain, relative weights of organs, mortality, behavior and morphological traits were also noted. Fish specimens in different treatment groups were exposed to varying concentrations of chlorpyrifos, namely: Treatment A = 0.3 micro g/L; Treatment B = 1.0 micro g/L; Treatment C = 1.6 micro g/L; and Treatment D = control. Exposure period was for 20 days and then fish were examined one, three, and ten days after cessation of treatments. Student's test revealed significant induction in cytochrome P450 levels. Test animals showed significant increase in red blood cell counts one, three, and ten days after the treatment period and in mean corpuscular volume and mean corpuscular hemoglobin one day after cessation of treatment. Moreover, significant increase in heterophils and a decrease in lymphocytes were noted in fish under Treatment C. Histological analysis showed an increase in the size of the melanomacrophage centers in the hepatopancreas of fish under Treatment C. No significant effect on the testes was detected. Though the residual levels of chlorpyrifos did not result in an immediate increase in the motality of the fish, results, however, show that it could still negatively affect the survival of the fish population in rice paddies in the long term
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