Effects of extremely low frequency alternating-current magnetic fields on the growth performance and digestive enzyme activity of tilapia Oreochromis niloticus

Extremely low frequency magnetic field (ELF-MF), as a ubiquitous ecophysiological factor, has been determined to influence the health of human and animals worldwide. In this study, we focused on the effects of ELF-MF on growth performance and digestive enzyme activity in juvenile tilapia, Oreochromis niloticus. Totally 450 fish were exposed to ELF-MF (50 Hz; 0, 30, 100, 150 and 200 mu T) for 30 days, respectively. The effects on growth and digestion were monitored on the 10th, 20th, and 30th day after induction (immediate effect), as well as 20th day after cessation of exposure (delayed effect). The activities of pepsin and intestinal protease of tilapia were significantly decreased after exposure in certain intensities of ELF-MF, but recovered when the ELF-MF exposure was removed 20 days later. Similar effects were also observed in the growth parameters, moreover interestingly, the specific growth rate (SGR) even represented a compensatory growth. To our knowledge, the present research provides the first determination that a certain extent of ELF-MF exposure could inhibit the growth and digestion of fish, and cause compensatory restorations after being removed upon a time.