Action of the magnetic field (72.5 Hz, 150 μT), solutions of Cu²⁺ ions (0.01 mg/l and 0.001 mg/l) and the combined effect of these factors on the eggs of roach Rutilus rutilus was studied. Survival and hatching rate of eggs, size-weight and morphological indices of fingerlings were considered. It is shown that the direction and intensity of biological effects caused by the combined effect of the magnetic field and Cu²⁺ solutions can be differ from the effects caused by these factors separately.