Effect of dietary Sargassum wightii and its fucoidan-rich extract on growth, immunity, disease resistance and antimicrobial peptide gene expression in Labeo rohita

This work aimed to appraise growth performance, immune responsiveness, bacterial disease resistance and mRNA expression of two antimicrobial peptides in Labeo rohita fingerlings fed diets supplemented with seaweed Sargassum wightii and its fucoidan-rich extract. Two hundred and twenty-five fingerlings were divided into five experimental groups in triplicates, each replicate having 15 fish in a 90-L tank. Different groups were fed with isonitrogenous (35% crude protein) and isoenergetic (1408.16 kJ/100 g) diets containing either 0% fucoidan-rich seaweed extract (FRSE), 1% FRSE, 2% FRSE, 3% seaweed powder and 6% seaweed powder for 60 days. Partial nucleotide sequences of the antimicrobial peptides, hepcidin and defensin, were characterized in Labeo rohita fingerlings, and gene expression in the different tissues of experimental fish was studied. The fish-fed FRSE-supplemented diets showed significant increase (P<0.05) in the mRNA expression of antimicrobial peptides in liver, skin and intestine tissues. Bacterial challenge study using Aeromonas hydrophila showed higher survival in the FRSE-fed groups. Fish-fed FRSE-supplemented diets also showed better non-specific immune response (NBT reduction, serum lysozyme activity, serum albumin: globulin ratio and phagocytic activity) in pre-challenge and post-challenge periods. No significant difference was observed in the growth performance in the different experimental groups. The study indicates that although dietary FRSE is a potential immunostimulant in Labeo rohita fingerlings, it does not improve growth performance.