Background. The magnetic field is known to exert its influence on both adult and juvenile fishes, as well as the embryos. The effects are diversified and pertain to, practically all, life aspects of an individual. Another aspect of this issue can be the existing and still growing magnetic pollution of the natural environment. In view of the above we decided to study the embryonic motorics of fish, exemplified by pike, affected by constant- and alternating magnetic fields. Materials and methods. Eggs of pike (Esox lucius L.) after period of adaptation (control) were subjected to 30-min action of the magnetic field (constant 4 mT and alternating 15 mT). The inflicted changes in the embryonic motorics were observed under a microscope and recorded on videotape. Results. The following aspects of the embryogenesis were affected: Quasi-peristalsis (increased angular velocity and the amplitude of ectoplasmic waves-at the stages of blastula end gastrula). Heart muscle action (in alternating field-short, small acceleration in the heartbeat is followed by a sudden rise of the number of contractions). Somatic motorics (no visible effect of neither constant- nor alternate field). Conclusion. Three different mechanism of the magnetic field are taken into consideration: a) directly on actomyosin structures in the quasi-peristalsis, b) on automatic centres of the developing heart, and c) on developing structures of the central nervous system (no effect presently observed).

magnetic field, fish, pike, embryonic locomotor activity