Effects of β-1,3-glucan and ascorbic acid on the nutritional-immune response and antioxidant signaling pathways of live tiger grouper during simulated transport

Transport in water is the most common method for transporting live fish in China, however, transport is a strong stressor. Transport stress could lead to a reduced immune and antioxidant system function of tiger grouper, resulting in sickness and death. Besides, tiger grouper were continuously stressed during transport, which resulted in quality deterioration. It is necessary that find a way to relieve the stress of transportation of tiger grouper. Ascorbic acid is not only a good anti-stress agent, but it is also an effective immunostimulant. β-1,3-glucan is a feed additive that can enhance the immune response of fish. Therefore, this study evaluated the effects of β-1,3-glucan and ascorbic acid on the nutritional-immune response and antioxidant signaling pathways of live tiger grouper during simulated transport. Results indicated that adding β-1,3-glucan and ascorbic acid in transport-water muted the increase of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity. In addition, β-1,3-glucan and ascorbic acid activated Nrf2 and mediated TOR expression and then up-regulate related mRNA expression of antioxidant and immune enzymes. We concluded that the application of β-1,3-glucan and ascorbic acid inhibit the increase of metabolism enzymes and inflammatory factors and activate immune and antioxidant signaling pathways to relieve oxidant stress, immune response, and apoptosis. Reducing the loss of amino acids provided nutrients to relieve oxidative stress and immune response, which demonstrated immune-nutritional response in live tiger grouper during simulated transport. These results may provide a new solution for alleviating the decline of immune and antioxidant function of tiger grouper caused by transportation stress.