In the present study, an attempt has been made to assess the acute toxic effect of cypermethrin (25%EC) on nucleic acids in different tissues of freshwater fish. Short-term acute toxicity tests were conducted by static renewal bioassay test, using different concentrations of cypermethrin. Fishes were exposed to sub lethal concentrations (5, 10, 15 and 20 per cent of 96h LC50 value) of cypermethrin for three different exposure periods, 5, 10 and 15 days. Decreased tendency was observed in both DNA and RNA in all the vital tissues of test fish exposed to cypermethrin over control. DNA and RNA contents were not altered by cypermethrin at 5 day exposure period. Both the nucleic acids gradually decreased with increased exposure period and the decrease was observed to be directly proportional to increased sublethal concentrations. The reduction in the DNA content in cypermethrin exposed fishes is comparatively less in muscle when compared to the other tissues studied. Maximum percentage of decrement in DNA was (17.17%) in liver and minimum was (13.94%) in muscle at the longest exposure period (15 days) and highest sublethal concentration (20% 96h LC50). RNA content decreased significantly in liver (29.90%), muscle (25.53%), brain (23.38%), kidney (21.82%) and gill (20.34%). The decrease was comparatively higher at 15 days exposure period at highest test concentrations. In all the organs studied, the influence of cypermethrin was found to be time and exposure period dependent.
