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

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 (R2 = 0.861), 0.385% at day 28 (R2 = 0.877), 0.371% at day 42 (R2 = 0.891) and 0.365% at day 56 (R2 = 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% (R2 = 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.