Immunostimulatory effects of dietary fucoidan from Padina boergesenii on growth, digestive performance, immune response and transcription of immune-related genes in Channa striata and disease resistance to Aeromonas hydrophila.

The objective of this research was to evaluate the antibacterial properties against Aeromonas hydrophila and histological responses, immunological mechanisms, gene expression and disease resistance in Channa striata. The fish were separated into five groups and given meals with various amounts of fucoidan diet (0%, 0.5%, 1.5%, 2.5%, and 3.5%) for 45 days. The study's findings show that adding 2.5% fucoidan to the diet resulted in a significant improvement in the final weight, weight gain, and specific growth rate (SGR) of C. striata. Furthermore, the feed conversion ratio (FCR) decreased significantly fucoidan fed groups. The dietary intake of 2.5% fucoidan resulted in an elevation in the levels of amylase, protease, and lipase enzymes. The antibacterial activity results showed significant dose-dependent antibacterial activities. The metabolic enzymes aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) were significantly increased. The antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) were also highly elevated during A. hydrophila infection and were modulated by fucoidan 2.5% supplementation in the diet. The supplementation of 2.5% fucoidan to fish diets enhanced non-specific immune responses such as Phagocytic activity, Nitroblue tetrazolium test (NBT), lysozyme activity, Complement C3, immunoglobulin (IgM) levels, and histological improvements after exposure to A. hydrophila. The fish-fed diets supplemented with fucoidan resulted in a significant increase (P < 0.05) in the mRNA expression of TNF-α and NF-κB in liver tissues. This study demonstrates that incorporating fucoidan to fish diets may promote growth, immunological and TNF-α and NF-κB increased, and resistance to A. hydrophila.