Effects of dietary n-6 polyunsaturated fatty acids (PUFA) composition on growth performances and non-specific immunity in pacific white shrimp (Litopenaeus vannamei)

This study was aimed to investigate the effects of dietary arachidonic acid (ARA) and linoleic acid (LA) on growth, fatty acid composition, antioxidant capacity and immunity of Litopenaeus vannamei. Eight diets were prepared with different LA or ARA content and approximately equal amounts of alpha-linolenic acid (ALA), eico-sapentaenoic acid (EPA) and docosahexaenoic acid (DHA), including a control diet (CK0) without ARA and LA supplementation. 720 shrimp were fed above diets in triplicate for 56 days. The results showed that, the specific growth rate (SGR) and weight gain (WG) of shrimp fed the experimental diets were significantly enhanced compared to the control group. In general, the content of LA or ARA in the experimental shrimp tissues closely mirrored their respective dietary fatty acid levels. The expressions of delta 6 fatty acid desaturase (delta 6FAD) and fatty acid elongase 5 (Elovl5) genes in the intestine and hepatopancreas increased significantly with increasing dietary LA from 5.3 to 9.5, or ARA from 0.2 to 11.1 g kg-1. The activities of superoxide dismutase (SOD) and catalase (CAT), and content of malondialdehyde (MDA) decreased with increasing dietary LA from 5.3 to 9.5, or ARA from 0.2 to 3.8 g kg(-1), then increased as dietary LA increased to 16.2, or ARA increased to 11.1 g kg(-1). The activities of lysozyme (LZM), acid phosphatase (ACP) and alkine phosphatase (AKP) increased accordingly with the increase of dietary LA from 5.3 to 9.5 or ARA from 0.2 to 1.9 g kg(-1). SOD and CAT gene expressions were opposite to the enzyme activity in ARA groups. The results suggested that appropriate dietary LA (9.5 g kg(-1)) or ARA (3.8 g kg(-1)) had positively effects on growth, EPA biosynthesis, antioxidant ability and immunity of L. vannamei.