Constant magnetic field of low value slows down the embryonic development of trout(Salmo trutta), rainbow trout (Oncorhynchus mykiss).Hatchlings were longer and heavier, and also more motile than those in the control experiment. Magnetic field induces a change in the circulation motion in embryos and larvae of pike(Esox lucius)and carp(Cyprinus carpio), and in the embryos of trout (5.tnitta).Exposure to magnetic field in embryos causes an increase in a heart rhythm, particularly during the early pulsation period of the forming heart. Magnetic fields cause a change in the gas exchange in embryos of a rainbow trout (O.mykiss).Intensity of breathing processes increase in a magnetic field, however, is dependent on stage of embryonic development, and it is especially manifested in the period of an advanced organogenesis. Embryos of rainbow trout (O.mykiss)and trout(S. tnttta)exhibit a sense of direction both in natural and artificially created magnetic field.