Dietary glycine supplementation enhances growth, feed utilization, and antioxidant capacity of large yellow croaker Larimichthys crocea
Abstract
Glycine is a dispensable and functional amino acid that promotes fish growth, however, the optimal glycine content in fish diets is not known. This study assessed the effect of dietary glycine content on growth, feed utilization, and antioxidant capacity of large yellow croaker (LYC) Larimichthys crocea . A diet containing 400 g/kg fishmeal served as the reference (R), and five low‐fishmeal diets (G0, G1, G3, G5, and G7) were formulated by substituting 60% of the fishmeal with a compound of rendered protein ingredients (CRP) in R and adding crystal glycine at 0, 1, 3, 5, and 7 g/kg, respectively. Dietary glycine contents of R, G0, G1, G3, G5, and G7 were 28.5, 28.9, 30.3, 32.2, 34.4, and 36.4 g/kg, respectively. Fish weighing 18.7 ± 0.2 g/ind. were fed the test diets in net‐pens for 8 weeks. Dietary glycine supplementation significantly affected final body weight (FBW), weight gain, nitrogen retention efficiency (NRE), feed conversion ratio (FCR), waste outputs, reduced glutathione (GSH) content and catalase (CAT) activity in liver, ratio of GSH to oxidized glutathione (GSH/GSSG) in plasma and liver, and protein‐carbonyl content in plasma. The FBW, weight gain, and NRE were higher, while the nitrogen waste was lower, in G5 than in G0. The regression equation indicated the maximum weight gain occurred at 35.3 g/kg dietary glycine content. Fish fed G0 exhibited lower GSH/GSSG in the plasma and liver compared with fish fed G5, and lower GSH content and CAT activity in liver, but higher plasma protein‐carbonyl content, compared with fish fed G3, G5, and G7. Fish fed R exhibited lower weight gain, plasma GSH content, liver CAT activity, and GSH/GSSG in plasma and liver compared with fish fed G5, and higher fishmeal reliance and plasma GSSG content compared with fish fed the low‐fishmeal diets. This study illustrates that appropriate glycine supplementation improved growth, feed utilization, and antioxidant capacity of LYC fed the low‐fishmeal diets, and the glycine content for maximum fish growth should be 34.4 to 35.3 g/kg.