The positive impacts of tea polyphenols on the growth performance, immune responses, and hepatic health of largemouth bass (Micropterus salmoides) under high fat diets

The objective of this study was to assess the impacts of tea polyphenols (TP) on the growth performance, immune responses, and hepatic health of largemouth bass ( M. salmoides ) under high fat diets. A total of 375 individuals (average initial weight: 34 ± 0.04 g) were divided into 5 treatments and fed diets with low fat (10 %, LF), high fat (18 %, HF), and HF supplemented with 40, 100 and 160 mg kg −1 tea polyphenols (named HFLT, HFMT and HFHT), respectively. The 60-day experiment revealed that the protein efficiency ratio (PER) was further enhanced in HFMT group, with notable variations found between HFMT group and fat groups ( P < 0.05). Final body weight (FBW), survival rate (SR) and weight gain rate (WGR) were unaffected by the fat and TP contents ( P > 0.05). Dietary TP levels significantly increased the activities of hepatic glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and catalase (CAT), and the contents of immunoglobulin M (IgM) ( P < 0.05), while decreased hepatic malondialdehyde (MDA) contents ( P < 0.05). The gene expression of hepatic bad , bax , rela , tnf-α and il-8 was down-regulated, while the expression of hepatic bag , tgf-β and the proportion of bcl-2 / bax were up-regulated by dietary TP levels ( P < 0.05), with no significant change in bcl-2 expression ( P > 0.05). Histopathological observations indicated that the TP-supplemented HF diets evidently diminished cell vacuolization and swelling, and enhanced the visibility of intercellular space. Meanwhile, a remarkably improved overall SR of largemouth bass following infection with Aeromonas hydrophila was found in TP-treated groups. In summary, the inclusion of TP in HF diets improved growth performance, antioxidant capacity and immune function of largemouth bass. Hence, based on our findings, the inclusion of 40–100 mg kg −1 TP in the HF diets of largemouth bass is recommended. • 40–100 mg kg −1 tea polyphenols (TP) enhanced the growth performance, immune and antioxidant capacity of largemouth bass. • 40–100 mg kg −1 TP was conducive to reduce fat deposits of largemouth bass. • 40–100 mg kg −1 TP contributed to the enhancement of hepatic health of largemouth bass. • 40–100 mg kg −1 of TP ameliorated the resistance to A. hydrophila. of largemouth bass.