The delayed consequences of the impact of a simulation of the main phase and the initial period of the recovery phase of a typical geomagnetic storm (SMRGMS) in the range of 0−0.001 Hz on roach (Rutilus rutilus L., 1758) embryos were studied. The embryos were exposed to SMRGMS with intensities of 100, 300 and 500 nT before (1−6 h post fertilization) and after (33−39 h post fertilization) gastrulation. The control group was under natural magnetic field. The size-mass, physiological and biochemical characteristics of underyearlings were evaluated. The length and mass of underyearlings exposed to SMRGMS after gastrulation were lower compared to the control. Amylolytic activity and the Michaelis constant (Km) of starch hydrolysis in intestine of fish from experimental groups were higher than in the control group. The relative enzyme activity in vital temperatures was higher and the temperature optimum of starch hydrolysis was wider and shifted to 40° C in fish from experimental groups as compared with the control (50° C). Maximum effects were revealed after the exposure of embryos to SMRGMS 100 nT after gastrulation. The magnitude and direction of observed effects depended on intensity of SMRGMS and time intervals in embryogenesis when the exposures were carried out.