Abstract:Large yellow croaker Larimichthys crocea is one of the most successful marine fish culture operations in terms of the number of juveniles produced and commercial size fish production annually in China. The production of this farmed species was more than 120000 metric tons in 2014 in China. However, large yellow croaker was often encountered with many stress situations, such as net cage changing, typhoon and water temperature oscillations during the grown-up farming. Generally, these could result in the decreases of feed utilization, anti-diseases ability and growth, even causing great economy losses. So, it is important to improve the anti-stress ability of large yellow croaker. The purpose of this study was to investigate the effects of dietary glycine on anti-oxidative and anti-stress responses of large yellow croaker (initial body weight 130.35±8.37 g). There were 6 experimental diets containing graded levels of glycine (1.58%, 2.15%, 2.75%, 3.96%, 6.33% and 7.51%) with different levels of glycine supplementation (0, 0.6%, 1.2%, 2.4%, 4.8% and 6.0%). After a 30 d feeding trial, the experimental animals were challenged with a 30 s trawl stress for three times. The results showed that the survival and body compositions of large yellow croaker had no significant differences among all the treatments (P>0.05). The significant highest value of the total anti-oxidative capacity in liver was found in the treatment with 2.75% dietary glycine. The lowest value of the malondialdehyde in liver was found in the treatment with 3.96% dietary glycine. However, this value of malondialdehyde did not significantly differ from that in the treatment with 2.75% dietary glycine (P>0.05). On the basis of hepatic total anti-oxidative capacity, using the second-order regression analysis, the most reasonable dietary glycine content for large yellow croaker was estimated to be 3.57%. Both the glutamic-oxaloacetic transaminase and the glutamic -pyruvic transaminase activities in serum had the lowest value in the treatment with 2.75% dietary glycine (P<0.05). Before the trawl stress, treatment with 2.75% dietary glycine resulted in the highest concentration of cortisol in serum (P<0.05). After the trawl stress, the serum cortisol concentration in this group kept little change. Meanwhile, the glucose concentration in serum kept at a relative higher level. In conclusion, for the purpose of improving the capacities of anti-stress in large yellow croaker, while had no significant negative effects on the survival and liver health, 2.75%–3.57% of dietary glycine were recommended for large yellow croaker.
