A Comparative Study on The Acute Toxicity Bioassay of Dimethoate and Lambda-cyhalothrin and Effects on Thyroid Hormones of Freshwater Teleost Fish Labeo rohita (Hamilton)

Dimethoate (organophosphate insecticide) and Lambda-cyhalothrin (synthetic pyrithroid) are two frequently used pesticides due to their high effectiveness and rapid breakdown into environmentally safe products. The aim of this present study was to assess and compare the acute toxicity of Dimethoate (Rogor30%EC) and Lambda-cyhalothrin (5%EC) on Labeo rohita (Hamilton). Acute toxicity bioassay was carried out in a static renewal system to assess the toxicity. The fishes were exposed to different concentration of dimethoate and Lambda-cyhalothrin to determine the LC50 values for 96hrs. The mortality data obtained were analyzed by SPSS 16.0 based on Finney’s Probit Analysis Statistical method. The 96h LC50 values for Dimethoate and Lambda-cyhalothrin were found to be 24.55 µl/L and 0.7 µl/L respectively. Effects of these two insecticides on serum T 3, T4 and TSH were investigated under sub-lethal toxicities which cause decrease in the serum T 3, T4 and increase in TSH level. It shows significant difference from control fish (p < 0.05)..