Effects of dietary administration of mannan oligosaccharides on growth performance, intestinal Vibrio, non-specific immunity and tolerance to low salinity in golden pompano, Trachinotus ovatus (Carangidae)

Abstract The effects of dietary supplementation with mannan oligosaccharide (MOS) on growth performance, haematological parameters, intestinal Vibrio , immune response, and stress tolerance to low salinity were evaluated in pompano ( Trachinotus ovatus ). Pompano (9.24 ± 0.15 g) were fed with 0 (control), 0.1, 0.2, 0.4, 0.6%, or 0.8% dietary mannan oligosaccharides for 8 weeks. The results showed that pompano fed 0.1–0.4% MOS had significantly improved (P < 0.039) specific growth rates. Dietary mannan oligosaccharides did not impact the survival rates of pompano (P = 0.192). The WBC was significantly higher in fish fed diets containing 0.1–0.6% MOS. Dietary MOS supplementation increased lymphocytes in pompano (P ≤ 0.042), while it reduced monocytes and basophils (P ≤ 0.019), but MOS did not show any effects on neutrophils and eosinophils (P ≥ 0.064). Intestinal Vibrio counts were reduced in pompano fed diets containing 0.1 to 0.4% MOS supplementation (P ≤ 0.035). The phagocytic ratio (PR) significantly increased in pompano fed diets containing 0.1 to 0.6% MOS (P ≤ 0.015), while the phagocytic index (PIs) and lysozyme in fish fed 0.1 to 0.4% MOS were significantly higher than fish fed control (P ≤ 0.035). There were significant positive correlations between MOS levels and fish growth at days 14, 28, 42, and 56 (P ≤ 0.049). In addition, dietary mannan oligosaccharide levels were highly correlated with blood parameters, intestinal Vibrio , and the immune index. Optimal dietary mannan oligosaccharides requirements for maximal growth of pompano were predicted to be 0.440% at day 21 (R 2 = 0.861), 0.385% at day 28 (R 2 = 0.877), 0.371% at day 42 (R 2 = 0.891) and 0.365% at day 56 (R 2 = 0.750), showing a reduction in MOS requirement when fish size increased. Furthermore, optimal MOS concentrations for maximal immunity based on lysozyme were predicted to be 0.431% (R 2 = 0.817) at day 56. Also, fish fed 0.1–0.4% MOS showed better resistance against low salinity stress (P ≤ 0.014). In conclusion, the 0.1–0.4% MOS supplementation could effectively enhance the growth, intestinal microbes, immune system, and tolerance capacity to the low salinity of the cultured pompano, T.ovatus .