Introduction
Nowadays, the aquaculture industry faces the challenge of reducing its dependence on fish oil and fishmeal. Therefore, it is of paramount importance to develop successful innovative aquafeeds which may contribute to achieving truly sustainable rearing practices. On such account, omnivorous low trophic level species like Chelon labrosus have been proved to provide optimal performance results when fed with alternative land-based protein diets (Sanz Latorre, 2024). What is more, novel diets have been also evidenced to influence the fish gut microbial community and its functionality, improving the fish nutrient utilization and enhancing their immune response (Agboola et al., 2023). For this reason, this research aims to formulate and test the impact of three alternative experimental diets on C.labrosus growth, microbial biodiversity and its functional role.
Materials and methods
Three isolipidic and isoenergetic diets were formulated using alternative ingredients and containing a 40% protein inclusion. The first one was 100% plant-based (V), the second one was a mix of vegetal and animal protein (VA) and the last one had a mixture of fishmeal and plant protein (FM). Then, 300 Chelon labrosus were kept in triplicate tanks and subjected to a 153 day trial phase in which they were administered the experimental diets. Zootechnical parameters were measured every 30 days. At the end of the experiment, 60 fish were sacrificed to obtain gastrointestinal tract samples for microbiome analysis. Composition and structure of the microbial community was assessed through the amplification and sequencing of the 16S rRNA gene. The bioinformatic analysis of the microbial metagenome was conducted using the Integrated Microbial Genome database, and the microbial functional annotation was based on the KEGG and COGs databases.
Results and discussion
Growth performance and nutritional parameters of Chelon labrosus with experimental protein sources.
Individuals that were submitted to the V treatment showed an overall higher growth performance as well as more efficient nutritional rates, whereas the VA group provided the lowest zootechnical parameters values (Table 1). Furthermore, the alpha and beta diversity metrics confirmed the V diet had a significant impact on the fish microbiome, revealing distinct taxonomic differences compared to the other experimental groups.
As for the taxonomical groups found in the fish GIT, all experimental treatments modified the initial fish gut microbial community. However, slight biodiversity differences were observed between the three analyzed treatments (figure 1). Despite not having found any significant difference between the treatment’s taxonomical biodiversity, the COGs and KEGGs terms analysis suggest that the experimental diets could have an effect in the fish gut microbial’s community functionalities.
Although many previous works have studied the viability of providing innovative feeds with alternative protein sources to different intensive aquaculture species, little is known when C.labrosus becomes the target species of the nutritional study. Therefore, despite the lack of knowledge regarding this species’ nutritional requirements, C.labrosus individuals reach optimal growth and zootechnical indexes when exclusively fed with vegetal protein-based diets. Such results could be due to the fact that inclusion of animal protein sources and hemoglobin affected the feed acceptability and palatability of the VA and FM pellets. This higher growth is aligned with a differential intestinal microbiota profile, as the Pseudomonas, Methanobacter and elusimicrobiaceae species that were exclusively found in the GIT from the V fish are known to have beneficial effects on nutrient digestion, fatty acids synthesis and immune defense boosting. In contrast, Vibrio cholerae proliferated in the fish gut of the VA specimens, which presence altered some physiological pathways (as observed in the KEGG analysis) and caused detrimental effects, having negative consequences to the fish growth and health.
Conclusion
In summary, the manufacturing of plant-based diets for low trophic species like C. labrosus leads the aquaculture industry towards an optimistic future in which the sector reduces its dependency on fishmeal and fish oil, becoming truly sustainable.
Acknowledgements
This study is part of the ThinkInAzul programme and has been funded by the Spanish Ministry of Science and Innovation with European Union NextGenerationEU funds (PRTR-C17.I1) and by the Government of Cantabria (Spain).
References
Agboola, J. O., Rocha, S. D. C., Mensah, D. D., Hansen, J. Ø., Øyås, O., Lapeña, D., Mydland, L. T., Arntzen, M. Ø., Horn, S. J., & Øverland, M. (2023). Effect of yeast species and processing on intestinal microbiota of Atlantic salmon (Salmo salar) fed soybean meal-based diets in seawater. Animal Microbiome, 5(1), 21. https://doi.org/10.1186/s42523-023-00242-y
Sanz Latorre, M. (2024). The thicklip grey mullet Chelon labrosus, as a candidate for intensive aquaculture diversification: optimization of culturing conditions and development of specific feeds based on alternative ingredients.