Effects of tea polyphenols on growth, antioxidant capacity and lipid metabolism related genes expression of turbot (Scophthalmus maximus)

In aquaculture, high fat diets are widely used for its protein sparing effect which can improve protein utilization efficiency, promote growth and protect environment pollution. Hoevever, it can also lead to excessive lipid deposition of liver and lower disease resistance. In order to solve this problem, additives should be explored. Tea polyphenols are natural plant extracts which have been proved to have the effects of of promoting growth, lipid reduction and immunity improving in many animals. Therefore, the purpose of the experiment is to investigate the effects of dietary tea polyphenols (TP) level on growth, antioxidant capacity and lipid metabolism of turbot. Four diets with graded levels of TP (0.00%, 0.01%, 0.02% and 0.05%. dry weight 0, 100, 200 and 500 mg/kg) was formulated in this experiment. Fish were cultured in indoor aquaculture system, and each diet was randomly assigned to three replicate groups of juvenile fish initial average weight of (13.51+0.31) g and fed twice daily (8:00, 18:00).The feeding trial lasted 70 d. The results showed as follows: ① Compared with the control group, fish fed the diet with 0.01%–0.02% TP had significantly higher weight gain rate (WGR). Feed efficiency (FE) was increased with the increasing TP level and no significant differences were detected among dietary treatments. Compared with the control group, Hepato-somatic index (HSI) was significantly increased by the supplement with TP. ② The lipid contents of whole fish and liver were decreased with increasing TP level and significantly lower in 0.02%–0.05% group compared with the control group. ③ Compared with the control group, the activities of total antioxidant capacity (T-AOC) and glutathione peroxidase (GSH-Px) were significantly higher in fish fed the diet with TP, and no significant differences were detected among fish fed diets with TP. The activity of superoxide dismutase (SOD) first increased and then decreased with the increasing TP level, and 0.02% supplement level was the highest. The content of malondialdehyde (MDA) was decreased with increasing TP level, and significantly higher in 0.02% group compared with the control group. ④ The expression of sterol regulatory element binding protein 1(SREBP-1) was decreased with increasing TP level and significantly higher in 0.02%–0.05% groups compared with the control group. The expression of fatty acid synthetase (FAS) was first decreased and then increased with increasing TP level and significantly lower in 0.02% group compared with the control group. The expression of peroxisome proliferator-activated receptor α (PPAR α) first increased and then decreased with increasing TP level and significantly higher in 0.02% group compared with the control group. The expression of carnitine palmitoyl transferase 1(CPT 1) increased with increasing TP level and significantly higher compared with the control group. This research indicated that high fat diets supplemented with TP could promote growth, reduce liver fat deposition, and increase antioxidant activity. The optimum supplemental level of TP in diets for turbot is approximatly 0.02%.