Feed additives are emerging as a suitable strategy to mitigate the potential negative effects of low fishmeal (FM) diets on fish growth and gut health. D ietary butyrate and taurine supplementation can reverse , at least partially, some of these drawback effects and alter the gut microbiota composition . However, their effects are underexplored in gilthead seabream ( Sparus aurata ) and other farmed fish. Thus, this study aimed to evaluate the potential benefits of butyrate and taurine dietary supplementation on fish performance and gut microbiota composition of gilthead seabream juveniles after 10 weeks of feeding and after crowding stressor exposure. To this aim, juveniles (~11 g) were fed with an FM-based diet (CTRL) or FM-free diet without supplementation (NOFM), supplemented with 0.1% butyrate alone (BUT), or with 0.1% butyrate plus 0.5% taurine (BUTTAU). After the nutritional trial , fish were exposed to a crowing stress for 10 days with a two-fold increase in rearing density. After the nutritional trial and after the stressor event, DNA from mucosal adherent bacteria from the anterior intestine was collected for the amplification and sequencing of 16 rRNA V1-V3 regions, using the Oxford Nanopore MinION . The best growth performance was achieved in fish fed the BUTTAU diet compared with CTRL , NOFM and BUT fish groups. In agreement with this, Partial Least Square-Discriminant Analysis (PLS-DA) of gut microbiota clearly separated NOFM fish, clustering together CTRL, BUT and BUTTAU fish with a high level of confidence (pR2Y=0.002; pQ2=0.002), explaining the two first components more than 96% of the total variance. Such separation was driven by 222 discriminan t taxa (VIPs ≥ 1) that comprised 9 abundant genera (at least 1% in one of the groups). Seven out of nine, including Photobacterium and Shewanella , were over-represented in NOFM fish and decreased in BUT and BUTTAU fish. The other two abundant discriminant taxa (Enterobacter, Escherichia ) decreased with the FM replacement and the BUT supplementation but increased again in BUTTAU fish. The key role of Enterobacter was depicted also by Bayesian network clustering , emerging as a pivotal parent node. On the other hand , it is of relevance that most of the gut microbiota changes driven by the matrix diet (CTRL vs NOFM) persisted after the stressor challenge, but the reshaping role of supplemented diets was transient, and it mostly disappeared after 10 days of crowing exposure. Altogether, the results reflect the important driving role of the environment upon gut microbiota, reinforcing the dynamic nutrition, environment, and microbiota interactions in farmed fish.
This work was supported by the TNA programme (PID:26681) within H2020 AQUAEXCEL3.0 project (871108) to I. García-Gallego for accessing to IATS-CSIC facilities, H2020 Marie Skłodowska-Curie ITN Programme (EATFISH; 956697), and by the Portuguese Foundation for Science and Technology (Ministry of Science and Higher Education, Portugal) through UIDB/04326/2020, UIDP/04326/2020 and LA/P/0101/2020 to CCMAR and contract DL57/2016/CP1361/CT0033 to CA. This abstract reflects the views only of the authors, and the European Union cannot be held responsible for any use which may be made of the information it contains.