Dietary mannan oligosaccharide enhances salinity tolerance and gut development of larval cobia

The potential beneficial effects of supplementing live feeds with mannan oligosaccharide (MOS; BioMos®) upon cobia Rachycentron canadum larval performance were examined. Characteristics of fish examined included survival to weaning, growth, ability to withstand osmotic stress and the degree of development of the brush border of the intestine. Live feeds included rotifers (Brachionus plicatilis) and Artemia which were enriched for 24 h with a commercial enrichment media alone or in combination with 0.2% (dry weight basis) MOS. Salinity challenges were performed at 6 days post-hatch (dph) and at 7, 13, and 14 dph (0 and 65 g L− 1 for 6 dph; 0 and 55− 1 7+ dph) corresponding to transitions in feeding, to examine the ability of larval cobia to survive stress. Differences (P < 0.05) in survival, favoring cobia receiving MOS-supplemented feeds were discerned at 6 and 7 days post-hatch (dph) when fish were challenged at 0 g L− 1 and at 13 dph when challenged with 55 g L− 1 salinity water. Electron microscopy of the mid-intestine of developing larvae revealed that MOS-supplemented diets enhanced (P < 0.05) the height of microvilli while reducing (P < 0.05) the occurrence and size of supranuclear vacuoles. Supplementation of diets with MOS could assist cobia larvae in maintaining allostasis especially when reared at sub-optimal salinities.