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Sustainable aquafeed production requires fishmeal replacement, leading to an increasing use of plant-derived ingredients. As a consequence, higher levels of antinutritional substances, such as non-starch polysaccharides and phytate, are present in aquafeeds, with negative effects on fish performance, nutrient digestibility and overall gut health. To alleviate these negative effects, providing exogenous digestive enzymes and/or probiotics can be an effective solution. In this study, we tested the effect of dietary supplementation of enzymes (phytase and xylanase) and probiotics (three strains of Bacillus amyloliquefaciens) on nutrient digestion kinetics and volatile fatty acid content along the gut, and the distal gut microbiome diversity in Nile tilapia. Chyme volatile fatty content was increased with probiotic supplementation in the proximal gut, while lactate content, measured for the first time in vivo in fish, decreased with enzymes along the gut. Enzyme supplementation enhanced crude protein, Ca and P digestibility in proximal and middle gut. Enzymes and probiotics supplementation enhanced microbial interactions as shown by network analysis, while increased the abundance of lactic acid bacteria and Bacillus species. Such results suggest that supplementation with exogenous enzymes and probiotics increases nutrient availability, while at the same time benefits gut health and contributes to a more stable microbiome environment.

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Background Fish gut microbial colonisation starts during larval stage and plays an important role in host’s growth and health. To what extent first colonisation could influence the gut microbiome succession and growth in later life remains unknown. In this study, Nile tilapia embryos were incubated in two different environments, a flow-through system (FTS) and a biofloc system (BFS); hatched larvae were subsequently cultured in the systems for 14 days of feeding (dof). Fish were then transferred to one common recirculating aquaculture system (RAS1, common garden, 15–62 dof), followed by a growth trial in another RAS (RAS2, growth trial, 63–105 dof). In RAS2, fish were fed with two types of diet, differing in non-starch polysaccharide content. Our aim was to test the effect of rearing environment on the gut microbiome development, nutrient digestibility and growth performance of Nile tilapia during post-larvae stages. Results Larvae cultured in the BFS showed better growth and different gut microbiome, compared to FTS. After the common garden, the gut microbiome still showed differences in species composition, while body weight was similar. Long-term effects of early life rearing history on fish gut microbiome composition, nutrient digestibility, nitrogen and energy balances were not observed. Still, BFS-reared fish had more gut microbial interactions than FTS-reared fish. A temporal effect was observed in gut microbiome succession during fish development, although a distinct number of core microbiome remained present throughout the experimental period. Conclusion Our results indicated that the legacy effect of first microbial colonisation of the fish gut gradually disappeared during host development, with no differences in gut microbiome composition and growth performance observed in later life after culture in a common environment. However, early life exposure of larvae to biofloc consistently increased the microbial interactions in the gut of juvenile Nile tilapia and might possibly benefit gut health.