Immune Response and Disease Resistance of Barramundi, Lates calcarifer (Bloch), Offered Diets Supplemented with Replete Levels of Tryptophan or Whey

Abstract

AbstractA basal diet containing 45% protein, 10% lipid, and 1.95% tryptophan (Trp) was formulated, and then supplemented with crystalline Trp (0, 0.1, 0.5, and 1% of the diet) or whey (16.9%) to evaluate the physiological effects of juvenile (initial weight: 0.57 ± 0.15 g) barramundi over a 58‐d rearing period. Significant reductions in growth and feed intake were observed in fish offered diets supplemented with Trp as compared to those offered the basal diet or the whey diet. Brain serotonin increased in fish fed the 1% Trp and whey diets albeit a decrease in cannibalism was not observed. Phagocytic activity, and Mx gene expression in spleens were not significantly changed among all groups. There were significant increases in lysozyme activity in the 1% Trp and whey groups, respiratory burst in the whey group, and Mx gene expression in head kidneys in the 1% Trp group 12 h after nerve necrosis virus (NNV) injection and in the whey 12 group and 24 h after NNV injection. Cumulative mortalities of fish fed the whey diet were significantly lower than those of fish fed the basal diet after Aeromonas hydrophila infection, but not Trp groups. Based on these results, diets supplemented with whey had reduced mortality when challenged with A. hydrophila and consequently function as an immunostimulant.