Dietary spermine supplementation enhances growth, protein synthesis, and antioxidant capacity in hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

Spermine, a natural polyamine, plays important roles in regulating growth, protein synthesis and antioxidant capacity of organisms. The purpose of this study was to assess the effects of dietary spermine supplementation on growth, protein synthesis and antioxidant capacity in hybrid grouper ( Epinephelus fuscoguttatus ♀ ×  Epinephelus lanceolatus ♂). Seven isoproteic, isoenergetic, and isolipidic diets containing different levels of exogenous spermine were formulated and fed to juvenile fish for 8 weeks. At the end of the feeding trial, nine fish were randomly selected from each tank and subjected to ammonia nitrogen stress for 57 h. The results showed that with increasing dietary spermine levels, the daily feed intake significantly decreased ( P  < 0.05), and significant cubic variations of protein efficiency ratio, protein productive value and dorsal muscle / body weight ratio were observed. There were no significant differences in serum growth hormone, insulin-like growth factor 1, spermine, and spermidine levels among the groups. The expression levels of target of rapamycin ( tor ), eukaryotic initiation factor 5 A ( eif 5 a ) and TOR phosphorylation level were also affected by dietary spermine. For gut histology analysis, only villus height of foregut was changed. After the ammonia‑nitrogen stress, there was a cubic correlation between spermine levels and cumulative mortality rate. The serum catalase, heme oxygenase 1 concentrations and the expression levels of NAD( P )H: quinone oxidoreductase 1 ( nqo 1) exhibited a cubic variation as dietary spermine levels increased. In summary, the optimal dietary spermine level for maximum percentage weight gain was estimated to be 19.9 mg/kg dry matter.