Synergistic effect of L-methionine and fucoidan rich extract in eliciting growth and non-specific immune response of Labeo rohita fingerlings against Aeromonas hydrophila

An experiment of 60 days was conducted to study the immunomodulatory response and growth performance of Labeo rohita fingerlings fed with fucoidan rich seaweed extract (FRSE) and methionine. Four hundred and twenty fingerlings were randomly distributed into seven different experimental groups in triplicates following completely randomised design (CRD). Fishes were fed to satiation with purified diets containing either 0% FRSE with 0.3% methionine (control), 0% FRSE with low dose (0.9%) methionine (T-1), 0% FRSE with high dose (1.5%) methionine (T-2), 1% FRSE with 0.3% methionine (T-3), 2% FRSE with 0.3% methionine (T-4), 1% FRSE with high dose methionine (T-5) or 2% FRSE with low dose methionine (T-6) in the feed. There was a significant (P < 0.05) effect of dietary fucoidan and methionine on the weight gain %, specific growth rate (SGR), feed conversion ratio (FCR) and protein efficiency ratio (PER) with highest weight gain % observed in the T-6 group. At the end of the experimental trial fishes were challenged with Aeromonas hydrophila and the highest relative survival percentage was recorded in the T-6 group, which was not significantly different from T-4 group (P > 0.05). Immunological parameters: respiratory burst activity, myeloperoxidase activity, lysozyme activity, total immunoglobulin, phagocytic activity and total leukocyte count (TLC) were increased with the 2% level of dietary FRSE along with low dose methionine, whereas serum albumin/globulin (A/G) ratio and blood glucose level showed a decreasing trend (P < 0.05). These results suggest the synergistic effect of FRSE and methionine for growth and immunity in contrast to the only immune boosting capacity of fucoidan. Thus, 2% FRSE along with low dose methionine can act as immunostimulant and growth promoter in the diets of L. rohita fingerlings.