Based on findings in various mammalian species, where exposure to electromagnetic fields decreased the nocturnal synthesis of the pineal secretory product melatonin, we investigated the effects of magnetic field (MF) exposure in a teleost fish, the brook trout (Salvelinus fontinalis). Fields were generated by Helmholtz coils (maximum flux density 40 microT, frequency 1 Hz, 200 ms on, 800 ms off). Melatonin concentrations were estimated by a specific radioimmunoassay. MF exposure significantly increased night-time pineal (P < 0.001) and serum (P < 0.01) melatonin levels, as compared with the controls. It is suggested that either the pineal glands are directly affected, i.e. by an increased Ca2+-influx into pineal photoreceptors, or that the responses are indirect since induced currents, caused by the rapid rise and decay of the generated MF, may have disturbed the sensory system for electric fields.

Neurosci Lett 1998 Nov 13;256(3):171-3
Lerchl A, Zachmann A, Ali MA, Reiter RJ.
Institute of Reproductive Medicine of the University, Munster, Germany.