To reveal which alternating magnetic field frequency falls in the field of efficiency upon survival and development for Daphnia magna, to determine if the magnet-biological effect depends on the stage of ontogenesis and to reveal if the exposure causes long-term effects.
Four different experimental variants were studied: 1) control-control, 2) control-exposure, 3) exposure-control and 4) exposure-exposure. The first part indicates the conditions under which Daphnia developed and matured, and the second part indicates under which conditions progeny was released. In the acute experiment, the magnetic field exposure lasted seven days and different frequencies (17 Hz, 50 Hz, 500 Hz, 5 kHz, 50 kHz, 200 kHz) were tested. Additionally, the frequency of 500 Hz was used for a chronic experiment (21 days).
Acute experiment: The alternating magnetic field with a frequency of 50 Hz had a weak stimulating effect upon maturation and survival of Daphnia magna. This could be due to the fact that the animals have lived for generations under laboratory conditions where they were exposed to 50 Hz fields and may have adapted to these conditions (preliminary assumption).
In all other trials, the effect was negative. The most negative effects upon survival and maturation were observed in D. magna exposed to alternating magnetic fields with the frequency of 17 Hz and 500 Hz.
Chronic experiment: Exposure to a frequency of 500 Hz during the juvenile stage of ontogenesis caused a malfunction in the reproduction program. This was manifested by an increase in the share of nonviable progeny and smaller body sizes of newborns from the first litters of parental daphnia exposed during the juvenile stage. Moreover, exposure to 500 Hz in a further reproductive period during the juvenile stage resulted in an increased number of newborns. The body sizes of newborns decreased, while the share of nonviable juvenils increased. The field thus had a long-term effect.