The effect of induced changes in gut microbiota on fish performance

Abstract

The establishment of the early-life gut microbiota plays an important role in fish development and influences the health status and growth performance of the host. The effect of different rearing conditions can have an impact on the initial colonization of the gut microbiota, while addition of probiotics may also affect such colonization. However, how this may affect fish larvae survival and growth remains largely unexplored. In this study, 3 day old Nile tilapia embryos were hatched until 9 days post fertilization (dpf) in three systems, including one flowthrough system (FTS) and two identical recirculating aquaculture systems (RAS). When feeding started at 10 dpf, tilapia larvae in the FTS and in one of the RAS were fed with a control diet, while larvae in the second RAS were fed with the control diet coated with B. subtilis spores (RASB). The feeding trial lasted 26 days, from larvae to fry stage, during which the survival, growth performance and gut microbiota were analyzed. The larvae reared in FTS showed significantly lower survival than the ones in RAS and RASB, while no differences were observed in fish growth and apparent feed conversion ratio between treatments. Different rearing systems resulted in different gut bacterial compositions which strongly correlated with the survival rate and standard body length at harvest. Cetobacterium was enriched in RAS and RASB, while it was barely detected in the gut of FTS-reared tilapia fry. Probiotic supplementation increased the relative abundance of beneficial Bacillus in fish gut. Our findings indicate that rearing fish larvae in RAS supports better survival compared to FTS, while dietary probiotic supplementation further modulates the gut bacterial composition and stimulates presence of beneficial bacteria during early life.