The present study aimed to unravel the effects of partial (50%; 50LSAqua) and total (100%; 100LSAqua) replacement of fish meal (FM) by a commercial protein source (LSAqua SusPro ) made of bacterial and processed animal proteins (PAP) in farmed juveniles of gilthead sea bream (Sparus aurata ). The trial lasted 8 weeks, and the feasibility of replacement was assessed in terms of growth performance, histopathological scoring and composition of mucosal adherent microbiota from anterior intestine (AI).
Specific growth rates (SGR) of 50LSAqua fish were undistinguishable from the CTRL group, whereas a slight but significant growth impairment was found with the total replacement. Histological signs of inflammation across the intestine were more evident at the highest level of FM replacement. Illumina sequencing of gut mucosal microbiota yielded a mean of 130,439 reads per sample assigned to 1,567 OTUs at 97% identity threshold. The bacterial richness was similar in all groups, but a significantly higher Simpson diversity index was found in 100LSAqua fish. At the phylum level, Proteobacteria were the most abundant in all groups, whereas Firmicutes decreased and Actinobacteria increased with the FM replacement.
Figure 0 : Inferred metagenome pathways found in fish fed with LSAqua diets in comparison with control. Green and red represent under- and overrepresented pathways, respectively.
The inferred metagenome analysis suggested that these discriminant bacteria could be implicated in a counter-regulatory anti-inflammatory response (Fig 1) .
It also pointed to an over-representation of mucosal microbes that can potentially be involved in the natural production of antimicrobials in fish fed the experimental diets.
Funding: This work was funded by the TNA programme (project ID AE170009) within H2020 AQUAEXCEL2020 project (652831) to DVM and PSJ for accessing to the facilities and services of Nutrigenomics and Fish Growth Endocrinology Group (2) and Fish Pathology Group (3) both from t he Institute of Aquaculture Torre de la Sal (IATS-CSIC), Castellón, Spain.
References: Solé-Jiménez, P., et al. , 2021. Frontiers in Marine Science, 8, 842. https://doi.org/10.3389/fmars.2021.705041