Variation in Gut Microbiota of Tilapia Larvae raised in Recirculating Aquaculture Systems and Active Suspension Tanks

Detmer Sipkema*, Christos Giatsis, Hauke Smidt, Marc Verdegem and Johan Verreth   Laboratory of Microbiology Wageningen University Dreijenplein 10 6703 HB Wageningen The Netherlands
Introduction: Baas Becking stated in 1934 that "Everything is everywhere, but the environment selects". This idea gives rise to the hypothesis that fish reared in different environments, such as Recirculating Aquaculture Systems (RAS) and Active Suspension (AS) tanks may lead to different microbiota in the water and gut. It may even lead to the development of different microbial profiles in different replicates of RAS or in different tanks that make part of the same RAS.
Experimental setup: We have studied the variation of microbiota in aquaculture systems at different levels: (1) variation within tanks, (2) variation between tanks, (3) variation between replicate RAS and (4) variation between RAS and AS tanks. The microbiota in water and tilapia larvae gut were monitored for 42 days by applying Denaturing Gradient Gel Electrophoresis (DGGE) in combination with 454-sequencing of PCR-amplified 16S rRNA gene fragments.
Results: Data from DGGE and 454-sequencing showed that variation in gut microbiota attributable to tank replication of the same system was not significantly higher than within tank variation. However, when individuals were reared in replicate systems, gut microbiota differed significantly (Fig. 1), and so did water microbiota. Lower variation in gut and water microbiota was measured between individuals reared in replicate systems, than between individuals reared in different systems (RAS vs. AS). Time also strongly influenced the microbial community in the gut, but to a lesser extent than the rearing system.
Conclusion: The choice of rearing system has a profound impact on the microbial communities present in tilapia gut and culture water, and may have implications related to fish health and nutrition management.