Effects of dietary lipid levels on growth, lipid metabolism, fatty acid composition and antioxidant capacity of juvenile greasyback shrimp (Metapenaeus ensis)

Abstract

The optimal dietary lipid requirement and underlying lipid metabolic mechanisms remain elusive in greasyback shrimp (Metapenaeus ensis), presenting significant obstacles to the advancement of their culture development. Five isonitrogenous diets (38.39% crude protein) containing lipid levels of 2.25%, 4.72%, 7.50%, 10.18%, and 12.71% were formulated to evaluate the effects of dietary lipid levels on growth, lipid metabolism, fatty acid composition and antioxidant capacity of juvenile greasyback shrimp. The results indicated that shrimps fed a diet with 7.50% lipid exhibited significantly higher percent weight gain (161.36%) and specific growth rate (1.72%/d) than those fed other diets (P < 0.05). As the dietary fat content increased, the lipid levels of the whole shrimp, muscle, hepatopancreas, and serum exhibited similar elevations. Concurrently, H&E staining clearly revealed the occurrence of hepatocyte swelling and hepatocyte vacuolization in the 10.18% and 12.71% groups, and hepatic lipid accumulation was further observed in these groups by Oil red O staining. In addition, with the increase in dietary fat levels, saturated fatty acids (SFA) decreased and polyunsaturated fatty acids (PUFA) increased in both hepatopancreas and muscle. The expression of genes involved in lipogenesis (fas, acc and dgat) was initially up-regulated and subsequently down-regulated with increasing dietary lipid levels, whereas the expression trends of lipolysis genes (hsl, atgl) remained similar. The mRNA levels of genes associated with long-chain PUFA biosynthesis (elovl5, lxrβ, srebp1) and fatty acid oxidation (cpt1, acox1) in the hepatopancreas of shrimp fed a diet with 7.50% lipid were significantly elevated compared to those in other dietary groups (P < 0.05). With the increase in dietary fat levels, the expression of fatty acid transport genes fatp4 and fabp1 was up-regulated. Antioxidant enzyme activities in the hepatopancreas initially increased with dietary lipid levels, peaking in shrimp fed the 7.50% lipid diet, but subsequently declined. In conclusion, optimal dietary fat levels enhance growth performance, while high lipid levels impede growth, decrease antioxidant enzyme activities, and regulate lipid deposition in greasyback shrimp by modulating lipid metabolic pathways.

Keywords

• Antioxidant capacity
• Fatty acid profile
• Growth performance
• Lipid metabolism
• Metapenaeus ensis