Use of fermented tea residues as a feed additive and effects on growth performance, body composition, intestinal enzyme activities, and inflammatory biomarkers in juvenile largemouth bass (Micropterus salmoides)

This study evaluated the effects of fermented tea residues (TF) on growth capacity, body composition, digestive enzyme activity, intestinal immunity, and inflammatory biomarkers in juvenile largemouth bass (Micropterus salmoides). For the study, four diets were produced: T0 (basal diet), T1, T2 and T3 replaced 2 %, 4 % and 6 % of the basal diet with TF, respectively. All fish were classified into four treatments at random, each of which included 20 fish and three duplicates and reared for 56 days. The results of our trials are as follows: 1) Supplementation with 2 % TF increased the weight gain rate (WGR), final body length (FL) and final body weight (FW) of juvenile largemouth bass (p < 0.05 ). 2) Compared with T0, intestinal protease, lipase and amylase activity increased in juvenile largemouth bass in T2 and T3 groups after supplementation with TF (P < 0.05 ). 3) Feeding TF significantly enhanced the alkaline phosphatase (AKP), superoxide dismutase (SOD), lysozyme (LZM), acid phosphatase (ACP), glutathione peroxidase (GSH-Px) and catalase (CAT) activities and total antioxidant capacity (T-AOC) level in the intestine of juvenile largemouth bass and reduced the malondialdehyde (MDA) content in the intestine compared with T0 (P < 0.05 ). 4) Supplementation with TF enhanced the mRNA expression of intestinal anti-inflammatory factors 1L-10 and TGF-β and reduced the expression of pro-inflammatory factors IL-1β, IL-15, TNF-α and IL-8 in largemouth bass (P < 0.05 ). In conclusion, supplementation with TF could promote growth performance, activity of intestinal digestive enzymes and increase intestinal immunity in juvenile largemouth bass, with a 2 % addition being the most effective.