Inclusion of condensed tannins in Lateolabrax japonicus diets: Effects on growth, nutrient digestibility, antioxidant and immune capacity and copper sulphate stress resistance

Condensed tannins (CT) possess antioxidant and immunostimulatory activities and thereby are regarded as a promising alternative to in-feed antibiotics. Although the effect of CT on growth of fish has been evaluated, little information is available about the effect of CT on the oxidative stress resistance of Lateolabrax japonicus. This study was conducted to assess the effects of CT on growth, nutrient digestibility, antioxidant and immune capacity and copper sulphate stress resistance of L. japonicus. A total of 960 juvenile L. japonicus (5.5 ± 0.11 g body weight) were randomly allocated into six groups with four replicates each (40 fish per replicate) and fed six diets containing 0, 0.2, 0.4, 0.6, 0.8 and 1.0 g/kg of grape seed CT respectively for 56 d. Fish were fed to apparent satiation twice daily during the entire experimental period and feces were collected daily for the last 14 d of feeding trial to determine nutrients digestibility using yttrium oxide as an indigestible marker. Fish were suffered with a 3-h acute copper sulphate stress test at the end of feeding trial. Blood and liver samples were collected to analyze antioxidant enzymes and non-specific immune indices, histomorphology and antioxidant-related genes expression. Dietary CT did not affect growth, body composition, liver histological appearance of fish but linearly decreased (P < 0.05) the intraperitoneal fat ratio, serum total cholesterol, triacylglycerol and tumor necrosis factor α as dietary CT increasing from 0 to 1 g/kg. Dry matter digestibility was linearly and quadratically decreased (P < 0.001), whereas digestibilities of organic matter, crude protein, crude lipid and ash were similar (P> 0.05) among treatments. Total antioxidant capacity (TAOC) and catalase (CAT) in serum as well as superoxide dismutase (SOD) and glutathione S-transferase in the liver were linearly increased (P < 0.01), and serum SOD and liver TAOC were linearly and quadratically increased (P < 0.05), whereas liver interleukin 6 was linearly decreased (P < 0.001) with the increased dietary CT concentrations. Expressions of SOD and nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA were up-regulated (P < 0.05) as dietary CT increasing, whereas expression of CAT and heat shock protein 70 (HSP70) mRNA were not affected by the treatments. Fish fed diets containing 0.8–1.0 g/kg of CT had lower (P < 0.05) cumulative mortality rate than those fed other diets as observed in the acute copper sulphate stress test. Superoxide dismutase and glutathione peroxidase in serum and TAOC and CAT in the liver were linearly increased (P < 0.05), liver CAT and Nrf2 mRNA were up-regulated (P < 0.05), whereas HSP70 mRNA was down-regulated (P < 0.05) with increased dietary CT concentrations. Dietary grape seed CT up to 1 g/kg did not affect growth and nutrient digestibility, but enhanced antioxidant and immune capacity as well as copper sulphate stress resistance of juvenile L. japonicus probably by activating Nrf2 signaling pathway. Condensed tannins are beneficial for the lipid metabolism of L. japonicus owing to decreased intraperitoneal fat ratio and blood lipid.