Introduction
Recent research has revealed the significant impact of novel feed ingredients on fish gut microbiota, affecting both the immune status and digestive performance. As a result, analyzing the microbiota modulatory capabilities may be a useful method for assessing the potential functionality of novel ingredients. Therefore, this study aimed to evaluate the effects of dietary polychaete meal (PM) from Alitta virens on the autochthonous and allochthonous gut microbiota of European seabass (Dicentrarchus labrax).
Materials and methods
Two diets were compared: a control diet with 25% fishmeal (FM) and a diet replacing 10% of fishmeal with PM, in 13-week feeding trial with Juvenile European seabass (Dicentrarchus labrax). Homogeneous groups of 40 fish were then distributed into 6 fiberglass tanks of 160-L in a saltwater re-circulation system. Each diet was randomly assigned to triplicate groups of fish, which were fed to apparent satiation three times daily (9h, 12h30, and 16h30) using automatic feeders. At the end of the trial six fish per tank were sacrificed for intestinal microbiota sampling. The intestine digesta was collected by squeezing. The autochthonous intestinal bacteria were collected by scraping the intestinal mucosa. Both digesta and mucosa were pooled into three groups of two fish per tank (n = 9 per dietary treatment). Additionally, 10 g of each feed was collected for analysis of the feed microbiota. All the samples were stored at room temperature until DNA extraction. The feed, digesta, and mucosa-associated microbial communities in fish intestines were analyzed using high-throughput sequencing of the 16S rRNA gene on the Illumina MiSeq platform.
Results and Discussion
The results of feed microbiota analyses showed that the PM10 feed exhibited a higher microbial diversity than the FM diet. However, these feed-associated microbiota differences were not mirrored in the composition of digesta and mucosal communities. Regardless of the diet, the digesta samples consistently exhibited higher species richness and diversity than the mucosa samples. Overall, digesta samples were characterized by a higher abundance of Firmicutes in PM-fed fish. In contrast, at the gut mucosa level, the relative abundances of Mycobacterium , Taeseokella and Clostridium genera were lower in the group fed the PM10 diet. Significant differences in metabolic pathways were also observed between the FM and PM10 groups in both mucosa and digesta samples. In particular, the mucosal pathways of caffeine metabolism, phenylalanine metabolism, and sulfur relay system were significantly altered by PM inclusion. The same trend was observed in the digesta valine, leucine, and isoleucine degradation and secretion pathways.
Conclusions
These findings highlight the potential of PM as an alternative functional ingredient in aquafeeds with microbiota modulatory properties that should be further explored in the future.
Acknowledgements
This work was subsidized by Project SIDESTREAM, funded through the ERA-NET BLUE BIOECONOMY COFUND by FCT (BLUEBIO/0005/2019). Part of the work was also funded by ATLANTIDA – Platform for the monitoring of the North Atlantic Ocean and tools for the sustainable exploitation of the marine resources” (NORTE-01-0145-FEDER-000040). CIIMAR acknowledges FCT funding (UIDB/04423/2020, UIDP/04423/2020). The authors would also like to thank Tiago Sá and Alexandra Marques for their help during the feeding trial and analytical work.