Two cohorts of 35 tadpoles were exposed during their immature period (whole larval stage) at two different magnetic flux densities and two comparable cohorts served as controls. The experiment was replicated three times (with litters from three different frog pairs).
The data showed that long-term exposure (about 60 days) of cohort tadpoles to an extremely low frequency magnetic field of 50 Hz caused a significant reduction of tadpoles mean developmental rate of 0.05 stages/day during the whole larval stage, that brought about an increase of 2.5 days in mean maturation time of exposed tadpoles compared to controls. Maturation rates of exposed and control tadpoles changed during the course of the maturation period. Mortality, malformations or teratogenic effects were not observed in exposed matured tadpoles.
The authors conclude that a long-term exposure of Xenopus laevis tadpoles to a relatively weak 50 Hz magnetic field causes a sublethal effect that slows down their larval developmental rate and delays their metamorphosis.