Influence of Electromagnetic Field and Thermal Stress on Physiological and Biochemical Parameters of Juvenile Prussian Carp Carassius gibelio with Different Mercury Content

The effect of short-term exposure to a low-frequency electromagnetic field (50 Hz, 10 μT) and thermal stress (water heating at a rate of 8°C/h) on amylolytic and proteolytic activities (AA and PA, respectively), maltase activity (AM) in the intestine, acetylcholinesterase (AChE) activity, and water-soluble protein (WSP) content in the brain of juvenile Prussian carp Carassius gibelio fed a specific diet for 2 months with low (LMC; 0.07 mg/kg wet weight) and high (HMC; 0.182 mg/kg wet weight) mercury content have been studied. After 1st and 2nd months of exposure mercury content in the fish muscles of the HMC group (0.40 and 0.66 mg/kg, respectively) was approximately 2 times higher compared to the LMC group (0.22 and 0.30 mg/kg, respectively). After 2 months of the experiment, AA increased by 30–48% and PA decreased by 30% only in the HMC group, however, no statistically significant differences have been revealed in the fish of the two studied groups. After two months of the experiment, the AM levels was 77% (LMC) and 340% (HMC) higher compared to the correspondent values after one month; furthermore, it was 36% higher in the HMC group than in the LMC group. No changes in the AChE activity were revealed either during the experiment or between the LMC and HMC groups. A comparison of the WSP content after the 1st and 2nd months of the experiment revealed a 40% decrease in the fish of the LMC group. The subsequent temperature stress (T) decreased AA and PA, while electromagnetic field (EMF) and its combination with T, as a rule, increased the activity of these enzymes in fish of both groups. A decrease in the activity of AChE (EMF + T) and WSP (T) was found only in fish of the HMC group. In general, mercury uptake with food increases the activity of the studied digestive enzymes, but does not affect the brain AChE activity. The WSP content decreases only in the 1st month of exposure to mercury. Subsequent temperature stress and the action of EMF can change the magnitude and direction of the effect. The obtained results are important for assessing the environmental risks of chronic mercury exposure in areas of thermal and electromagnetic pollution of water bodies.