Effects of dietary selenium levels on growth performance, antioxidant capacity and related gene expression of juvenile turbot (Scophthalmus maximus) under copper stress

The study was carried out to investigate the effect of dietary selenium(Se) supplementation on the growth performance, serum antioxidant enzyme activity and expression of related genes in liver of juvenile turbot (Scophthalmus maximus) under copper(Cu) stress. Four experimental diets(D1,D2,D3,D4) were formulated to contain the following diets with increment levels of copper 0, 1 000, 1 000, 1 000 mg/kg and selenium 0, 0, 2, 4 mg/kg. The group D1 as the control. Each diet was randomly assigned to triplicate groups of 40 fish initial weight, (24.85±0.1) g per aquarium. Fish were fed twice daily(8:30 and 16:30) at ratio of 1.5% or 2% body weight for 84 days. Results showed that the different diets had no significant effect on the survival rate of turbot. The weight gain rate, specific growth rate and protein efficiency ratio of D2 group were significantly lower than other groups. Whereas, feed conversion ratio and feed intake reached the maximum in group D2. Crude lipid content of whole body and liver all showed a trend of first decreasing and then rising, and, there were no significant differences of crude lipid and crude protein contents in muscle among all groups. Cu concentration of D2 group in whole body, vertebra and liver was remarkably higher than the others. Zn concentration in whole body, vertebra and liver reached the maximum in the group D4. Hepatic Fe concentration was lower in group D4 than the others. The serum total antioxidant activity, catalase activity, glutathione peroxidase activity decreased in group D2, and increased with further increase of selenium level. While the malondialdehyde content followed the opposite trend. Total superoxide dismutase and CuZn superoxide dismutase activity both reached the minimum in group D4. Both alanine aminotransferase and aspartate transaminase activities showed their highest values in group D2, which were significantly higher than those in the other groups. Glucose, triglyceride, total cholesterol, high density lipoprotein cholesterol, low density lipoprotein cholesterol showed a opposite trend to alanine aminotransferase and aspartate transaminase activities with the lowest value in group D2, significantly lower than that in the control group. Metallothionein expression increased in the liver with the dietary selenium levels under Cu stress, which was significantly higher in group D4 than that in the other groups. Glutathione transferase and lysozyme expression levels decreased initially and then increased with the dietary change, which were significantly lower in group D2 than those in the control group. Heat shock protein 70(HSP70) expression level showed the highest values in group D2, which was significantly higher than those in the other groups. In conclusion, adequate dietary selenium levels could affect the growth performance, increase the total antioxidant capacities, modulate some mRNA expression of gene in liver, and then reduce the metabolic disorders caused by high copper content in juvenile S. maximus.