Influence of two organochloride pesticides, Thiodan and Lindane on survival of fingerlings of Oreochromis niloticus (Linnaeus) and Tilapia zillii (Gervais)
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Toxic effects of two organochloride pesticides, Thiodan and Lindane on two tilapia species, Oreochromis (= Sarotherodon) niloticus and Tilapia zillii, were investigated in fresh water at 25–30°C under laboratory conditions. In the case of Thiodan LT 50 (median lethal time) values increased from 78 minutes at 1 ppm to 6.5 days at 0.001 ppm for T. zillii. As for Lindane the LT 50 values increased from 60 minutes at 2 ppm to 4.7 days at 0.125 ppm for O. niloticus while the corresponding LT 50 value s for T. zillii were 46 minutes and 2.7 days. No fish died within one week exposure at 0.0625 ppm Lindane for both O. niloticus and T. zillii. Median lethal concentrations (LC 50), obtained from regressions of pesticide concentrations and LT 50, indicated that the 96 hour LC 50's for Thiodan and Lindane were 0.00142 and 0.11590 ppm for O. niloticus, while the corresponding values were 0.00083 and 0.00597 ppm respectively for T. zillii. The safe concentration of Thiodan for O. niloticus was e stimated as 0.000588 ppm while that for T. zillii was 0.000321 ppm, and for Lindane the safe concentration was 0.0232 ppm for O. niloticus and 0.000762 ppm for T. zillii. The results showed that Thiodan was about 50 times more toxic than Lindane to O. niloticus and about 6 times more toxic than Lindane to T. zillii.