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) aretwo frequently used pesticides due to their high effectiveness and rapid breakdown into environmentally safeproducts. 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 wascarried out in a static renewal system to assess the toxicity. the fishes were exposed to different concentrationof dimethoate and lambda-cyhalothrin to determine the lc50 values for 96hrs. the mortality data obtainedwere analyzed by spss 16.0 based on finney’s probit analysis statistical method. the 96h lc50 values fordimethoate and lambda-cyhalothrin were found to be 24.55 μl/l and 0.7 μl/l respectively. effects of thesetwo insecticides on serum t3, t4 and tsh were investigated under sub-lethal toxicities which cause decrease inthe serum t3, t4 and increase in tsh level. it shows significant difference from control fish (p < 0.05)..