Reevaluation of dietary condensed tannins on growth, antioxidant and immune response and muscle quality of Chinese seabass (Lateolabrax maculatus)

Abstract

Chinese seabass (Lateolabtax maculatus) is a popular carnivorous fish that is widely cultured in China in recent years. Previous studies suggested that low dose of CT enhanced antioxidant and immune response, but high dose of CT inhibited growth and induced tissue damage of fish. Meanwhile, information regarding effects of CT on muscle quality of L. maculatus is limited. A 63-day feeding trial was performed to assess the effects of dietary CT on growth, antioxidant and immune response and muscle quality of L. maculatus. Four diets were formulated to contain 0 g/kg of CT (G1), 1 g/kg of CT (G2), 2 g/kg of CT (G3), and 2 g/kg of CT plus 4 g/kg of polyethylene glycol (PEG) (G4, as positive control). PEG specifically binds with CT to neutralize CT activity. Fish were randomly distributed into 16 tanks with 4 tanks per diet and 40 fish per tank, and were fed to apparent satiation twice daily during the feeding trial. Results indicated that dietary CT at the concentration of 1 g/kg did not alter (P > 0.05) growth and feed utilization of L. maculatus. Fish fed G3 had lower (P < 0.05) final body weight, weight gain rate, thermal growth coefficient and feed intake than those of fish fed G1, G2 and G4. Fish fed G3 had lower (P < 0.05) total feed intake than those fed other diets in the 1, 2, 3, 4 and 5 week of the feeding trial. As compared with G1, serum catalase and superoxide dismutase activities were higher (P < 0.05) in G2, lower (P < 0.05) in G3, and similar (P > 0.05) in G4. Serum lysozyme activity and immune globulin M concentration were higher (P < 0.05) in G2 and G3 than those in G1 and G4. Muscle fiber density was increased (P < 0.05) as dietary CT increasing from 0 to 2 g/kg, but was similar (P > 0.05) between G1 and G4. Muscle water loss rate of post thawing was higher (P < 0.05) in G2 and G3 than that in G1 and G4, but was similar (P > 0.05) between G1 and G4 as well as G2 and G3. All fish had similar (P > 0.05) muscle amino acid compositions. Fish fed G3 had lower (P < 0.05) mRNA relative expressions of GH, IGF-1, Myf5, MyoD and Pax7 than those of fish fed other diets. The mRNA relative expressions of GH, IGF-1, Myf5, MyoD and Pax7 were similar (P > 0.05) among G1, G2 and G4. All fish had similar (P > 0.05) RNA relative expressions of IGF-2, MyoG and Mstn2 among groups. In summary, inclusion of 1 g/kg CT in L. maculatus diets did not alter growth but enhanced serum antioxidant and immune response, whereas 2 g/kg of CT declined feed intake and growth, decreased antioxidant enzyme activities but enhanced immune response of fish. Supplementation of CT increased muscle fiber density, decreased muscle water holding capacity but did not affect muscle amino acid compositions of L. maculatus. Dietary CT at the concentration of 2 g/kg down-regulated the majority of muscle growth-related genes expression, which may account for the decreased growth performance of L. maculatus.