Aquaculture industry is con tinuously interested in a deeper understanding of the impacts of farm practices on the nutrition and health of targeted species with the aim to improve and adjust its sustainable development. It is well known that fish intestinal microbiota has strong interactions with numerous physiological processes lik e immune responses, homeostasis and metabolism among others. Intestinal microbiota composition fluctuates depending on various parameters, including species, diet, environmental conditions and the exposure to chemical components like antibiotics, w hich can lead to rapid emergence of resistant bacteria threating global human health.
A 130 -days feeding trials was performed in open circulating aquaculture system on healthy Sparus aurata (8.3g initial body weigth , n=48 fish/50L tank, 4 replicates, water temperature of 20°C±2 ) receiving a 90-days feed supplementation of a marine probiotics consortium constituted of four marine Bacillus strains encapsulated in algae (marine symbiotics) to evaluate, first of all, the positive modulation on the intestinal microbiota in normal condition. Supplementation was then stopped and a 10-days antibiotic treatment with oxytetracycline (OTC, 90 mg of active principle/kg) was administered before a new period of 30-days of supplementation with marine symbiotics. A control group fed with a conventional food instead of probiotics underwent the same antibiotic treatment. P robiotics presence in intestinal tract (qPCR with specific probiotics strains primers ) and evolution of microbiote composition (metabarcoding) before and after the OTC treatment and at the end of the 30-days supplementation period was analyzed . The well known dysbiosis induced by OTC treatment in healthy gut microbial community will be presented (on going analysis) . Dietary inclusion impact of marine symbiotics after OTC treatment will be shown on the intestinal microbiota recovery. We already demonstrated that t he colonisation of intestinal microbiota by marine symbiotics was associated with the emergence of other beneficial bacterial. T his study characterized the dysbiosis induced by an antibiotic treatment on fish gut microbiota and how marine symbiotics could enhanced and improved the restoration of the intestinal flora in an innovative way to limit negative impact on fish health and economic loss. A similar study on Salmon salar from commercial farm are on going to confirm results of the present study.