Subacute and chronic intoxication of copper sulphate on goldfish and carp were tested under lower concentrations than those in usual cases of TLm test in 24 or 48 hours.The effects were measured, in tanks containing the water of 48 or 50l with 5 fish of similar size placed as one experiment lot, referring to the maximum and minimum periods of survival (days), the growth in length and weight of body, the condition factor and amount of food consumed. The temperature of the water was kept at 23±1°C, and pH value at 5.7±0.1 during the test extending the maximum of 30 days.Also, seven kinds of copper compounds were examined on the survival (in hours) of carp. The tests revealed, among others, that the concentrations which permitted the survival of more than 30 days were 0.17 ppm for goldfish, and 0.08 for carp in the maximum and that the growth showed lowering at 0.08 ppm for goldfish and 0.024 for carp in the minimum. The amount of food consumed decreased to 70% at the concentration of 0.008 ppm in carp against 100% at 0ppm, though the fish survived more than 30 days in apparent healthy condition at this low concentration.The decrease of intake of food by carp was believed to have resulted from the toxic effects of copper sulphate on the mucous epithelia and on the enzymes in the digestive tract as usually observed in mammals. Discussion was made from the results of the present study and from literature referring to the so-called safety concentrations of copper compounds, which are often applied for the extermination of parasitic animals and plants to fish.The concentrations of copper sulphate used for such purposes range from 500 to 0.04 ppm.The safety level has been often calculated from the TLm in 24 or 48 hours. However, the results gained in the present study will indicate that the allowance on the safety concentration of copper sulphate of fish should be made on the basis of the bioassay tests aimed to the seeking of the concentrations which effect subacute or chronic intoxication rather than on usual TLm test in shorter periods as above mentioned.