Dietary ascorbic acid and eicosapentaenoic acid in abalone Haliotis discus hannai: Size-dependent interactions on lipid metabolism and immunity

Abstract

A 93-day feeding trial was conducted to examine the effects of dietary eicosapentaenoic acid (EPA) and ascorbic acid (AA) on the immunity and lipid metabolism of two different sizes of abalone Haliotis discus hannai, with initial weights of 26.89 ± 0.26 g for large-sized and 4.11 ± 0.10 g for small-sized abalone. A 3 × 2 two-factor design was employed to formulate the six experimental diets, consisting of three levels of dietary EPA (0.25 %, 0.75 %, and 1.25 %) and two levels of dietary AA (0 and 1260 mg/kg). The results revealed that in the 1.25 % EPA-supplemented groups, the content of total triacylglycerol (TG) was significantly increased, while low-density lipoprotein cholesterol (LDL-C) was decreased in the cell-free hemolymph (CFH) of large-sized abalone, regardless of dietary AA levels. The TG and LDL-C contents were significantly increased in the CFH of a small-sized abalone fed diet with 1260 mg/kg AA. Dietary supplementation of EPA and AA changed the fatty acid compositions in large- and small-sized abalone by mediating the expression of lipid metabolism-related genes (such as pparα, hsl, atgl and srebp-1c). Additionally, the impact of EPA and AA on immune function was equally notable. Supplementation of 1260 mg/kg AA and 1.25 % EPA in the diet increased the anti-oxidation and immune enzyme activities, and downregulated the levels of pro-inflammatory factors, and thus improving the anti-oxidation and immune abilities of abalone. In summary, there was an interaction between EPA and AA on the immunity and lipid metabolism in abalone. Supplementation with 1.25 % EPA and 1260 mg/kg AA had a more pronounced effect on large-sized abalone than smaller ones, including enhancing the lipid metabolism, immunity and overall health status. These findings implied the importance of developing dietary supplementation strategies for abalone, and the size of abalone is an important factor in determining the most effective approach.