Characterization of the bacterial community in tilapia (Oreochromis niloticus) production systems by the In Situ Fluorescent Hybridization technique (FISH)
To increase the growth of aquaculture, there is an urgent need to optimize production systems, making them increasingly efficient and environmentally friendly. The bacteria present in aquaculture systems are of great importance for their better functioning and health. Thus, understanding the interaction of the microbiota with the animals produced is important to establish strategies for disease control and water quality management. For this, quickly and accurately quantifying and identifying the bacterial community is essential to improve production conditions. In this thesis, a molecular biology technique, Fluorescent In Situ Hybridization (FISH), was used,to identify and quantify bacteria in order to (1) identify the similarity of the bacterial community in the intestinal tract of tilapia (Oreochromis niloticus) with the production environment (water and sediment); (2) to verify the colonization efficiency and action of a potentially probiotic bacterium, previously isolated from the production system itself and (3) to evaluate variations of groups of nitrifying bacteria in the water and biofilm in a water recirculation system (RAS) for tilapia production. In chapter 1, we observed that the composition of the bacterial community in the gastro-intestinal tract of tilapia was more similar to the water community, compared to the microbiota of the nursery sediment. In chapter 2, Bacillus sp., Which has great probiotic potential and was isolated from the production system itself,presented great abundance in the intestines of tilapia, after being offered together with the feed. This indicated a good incorporation of this isolate into the microbiota of the intestinal tract of these fish. Bacillus sp. was able to control two species of pathogenic bacteria, which showed less abundance in the presence of this probiotic microorganism. In chapter 3, it was observed that the nitrification process in the RAS is mainly related to the nitrifying bacteria present in the biofilm, but not in the water. In general, the FISH technique was effective in monitoring the qualitative and quantitative changes of the bacterial communities in all the works developed. Thus, we can say that this technique showed great potential for future studies on the ecology of microorganisms in aquaculture systems.