Fresh water fish, Motsugo was reared in aquarium water tank containing about 1 ppm of 3 organophosphorus and 3 carbamate insecticides for about 30 days. The persistence of these insecticides in water and uptake and excretion of insecticides by fish were examined. Among organophosphorus insecticides, malathion is the most unstable in water, and degraded more than 99% for 7 days. Fenitrothion is moderately stable, and degraded 97% for 29 days. Diazinon is the most stable, and degraded 72% for 30 days. Among carbamates, carbaryl is the most unstable in water, and degraded more than 95% for 6 days. BPMC is moderately stable, and degraded 80% for 32 days. XMC is the most stable, and degraded 45% for 34 days. As for the uptake of the pesticides by fish, organophosphorus insecticides were generally higher than carbamate insecticides. The concentration of diazinon in fish reached to 211 ppm of the maximum level after 3 days, and that of fenitrothion reached to 162 ppm of the maximum level after 4 days. Afterwards, the concentration of both the insecticides decreased gradually due to the metabolism and excretion of the insecticides in fish. Uptake of malathion was very low and metabolized rapidly, and its concentration became to less than 0.01 ppm after 7 days. Among carbamate insecticides, the concentration of carbaryl in fish after one day reached to 7.5 ppm which was the maximum level of uptake. On the other hand, the concentration of BPMC in fish after 4 days became to 4.8 ppm, which was the maximum level, and decreased gradually. The concentration of XMC in fish was only 1.4 ppm after one day, but the metabolism rate of XMC in fish was fairly slow. Therefore, 0.55 ppm of XMC in fish remained even after 34 days. Moreover, in the test tank of diazinon, fenitrothion and BPMC, the appearance of deformed fish with spinal curvature of back bone came out at the rate of 10 to 30%.