Dietary mannan oligosaccharides elevated growth performance, gut morphology, microbiota, body composition, feed and nutrient utilisation of pompano, Trachinotus ovatus

Pompano (Trachinotus ovatus) is a highly economical aquaculture species; however, intensive aquaculture of pompano is associated with pathogen infection, environmental stress, drug and chemical use, causing reductions in growth, survival and economic losses. Mannan oligosaccharide (MOS) is a prebiotic that has been reported to boost the growth and health of many species; however, no study has examined the effects of MOS on pompano. In the present study, the effects of dietary MOS levels on growth, body composition, intestinal microbiota, feed, and nutrient utilisation in juvenile pompano were investigated over an 8-week experiment. Five diets containing five levels of MOS (0.1%, 0.2%, 0.4%, 0.6%, and 0.8%) were fed to pompano (mean weight, 5.16 g±0.05). The results indicated that pompano fed 0.1–0.40% MOS in the diet had the highest growth performance (p ≤ 0.009), but fish fed 0.6–0.8% MOS had no impact on growth (p ≥ 0.056). MOS had no effect on the survival rate of pompano (p ≥ 0.327). The gut surface area increased in fish fed 0.1–0.4% MOS (p ≥ 0.011), but not in fish fed 0.6–0.8% MOS (p ≥ 0.102). Total aerobic bacteria (TAB) increased in fish fed 0.1–0.4% MOS (p ≤ 0.017), but TAB was not affected at 0.6–0.8% MOS (p = 0.315), whereas Vibrio count and ratio of Vibrio to TAB significantly reduced in fish fed any levels of MOS (p ≤ 0.024). Feed conversion ratio (FCR) significantly reduced (p ≤ 0.019), while feed conversion efficiency (FCE) significantly increased (p ≤ 0.014), when pompano were fed a diet containing 0.1–0.4% MOS. Protein in fish increased in fish fed a diet providing 0.1–0.4% MOS (p ≤ 0.011), but when adding higher levels of MOS (0.6% and 0.8%) to the diets, the protein content in fish did not change (p ≥ 0.072). Lipid content was significantly reduced in fish fed 0.1–0.4% MOS (p ≤ 0.035), but not at higher levels of MOS (p ≥ 0.085). The protein efficiency ratio (PER), lipid efficiency ratio (LER), and lipid productive value (LPV) boosted in fish fed diet containing 0.1–0.6% MOS (p ≤ 0.029). Protein productive value (PPV) increased in fish served diet containing 0.1–0.4% (p ≤ 0.008). Those values did not change with 0.8% MOS (p ≥ 0.137). MOS levels had positive correlations with growth performance, FCE, PER, PPV, LER, LPV and TAB (r ≥ +0.481, p ≤ 0.001), while MOS levels showed negative correlations with intestinal Vibrio and FCR of pompano (r ≥ −0.562, p ≤ 0.003). The optimal levels of MOS were 0.424% for pompano's lowest FCR, while the be