The effects of pulsing magnetic fields on pineal melatonin synthesis in a teleost fish (brook trout, Salvelinus fontinalis)

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 μT, 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.