Genetically superior European sea bass (Dicentrarchus labrax) and nutritional innovations: Effects of functional feeds on fish immune response, disease resistance, and gut microbiota

The objective of this study was to determine if selected fish genotypes could benefit from the use of functional additives in novel aqua feed formulations to improve growth performance, gut microbiota, immune response, and disease resistance in fish. Two batches of juvenile European sea bass selected for high growth (HG; selected sires x selected dams), and wild types (WT; wild sires x selected females) were fed a “future diet” coated with three different functional additives for 12 weeks as follows: (i) 2 weeks with a high dose, followed by (ii) 10 weeks with a low dose. The functional additives tested were a mixture of probiotics (PROB), organic acids (ORG), and phytogens (PHYTO). A pathogen challenge test (Vibrio anguillarum) and a stress condition (overcrowding) were performed after each dose. At the end of the feeding experiment, fish from the HG group performed better than fish from the WT group in terms of body weight, relative growth, SGR, and DGI. The results of the two challenge tests performed after two weeks of high dose and ten weeks of low dose showed a significant effect of diet on fish survival. GALT-associated gene expression analysis revealed an interaction between the genotype and diet for il-1β in the distal gut. Finally, regarding the gut microbiota, discriminant analysis showed no clear separation between fish fed the future diet and those fed the same diet with experimental additives. Nevertheless, the relative abundance of certain taxa varied between experimental groups. For example, fish fed the ORG diet had higher relative abundance of Streptococcus in both genotypes, whereas fish fed the PHYTO diet had higher abundance of Lactobacillales. In contrast, fish fed PROB had lower bundance of Pseudomonas and Acinetobacter

The genetic background drives the reshape of gut microbiome by feed additives in farmed gilthead sea bream (Sparus aurata)

Resumen del trabajo presentado en 6th International Symposium on Genomics in Aquaculture, celebrado en Granada (España) del 04 al 06 de mayo de 2022.The use of feed additives has expanded rapidly as an alternative for antibiotics and chemotherapeutics, with also the capacity to modify the composition of gut microbiota. In farmed fish, and in gilthead sea bream in particular, there is evidence that the host genetic background has a major impact on gut microbiota. Thus, families selected for fast growth have a more flexible microbiota capable of exerting a wider nutritionallymediated response with less microbial community changes. However, nutrition and genetic interactions remain poorly explored in fish, and the aim of this study was to unravel how the microbiota of fish selected (GS) and unselected (NGS) for growth is differentially regulated by oil-coated feed additives. The basal diet (CTRL, no feed additives) was a low fish meal/fish containing algae oil, poultry by-products, and plant ingredients. Experimental diets were oil-coated with the additives: organic acids (OA), Bacillus-species probiotics (PROB), or natural plant extracts (PHYTO). Fish were fed to visual satiety with the CTRL diet during two weeks. After this adaptation period, the different supplemented diets were used with a high additive dose (7.5-10 g/kg) during 2 weeks, decreasing thereafter to 2-5 g/kg until the end of the trial (97 days). Then, adherent microbiota was obtained from the anterior intestine. Illumina sequencing of microbiota yielded a mean of 62,594 reads per sample, which were assigned to 1,156 OTUs at 97% identity threshold. A significant lower richness and diversity was found in the GS fish, which was mainly evidenced by a higher abundance of Actinobacteria in GS-PROB. To study in more detail the observed differences on gut microbial populations, supervised partial least-squares discriminant analyses (PLS-DA) were used. When all populations were analysed as a whole (GS vs NGS), dispersal was markedly lower in GS fish. This pattern was further evidenced for fish fed the CTRL, PROB and OA diets but not for the PHYTO additive, explaining the statistically validated PLS-DA models more than 80% of the total variance. This genetically-guided group differentiation was driven by a total of 104 OTUs. Regarding diet and genetic interactions: i) no effect was detected with the PHYTO additive, ii) the OA reshaped the gut microbiota in NGS with a decrease of Photobacterium damselae sp. and an increase of Paracoccus and Acinetobacter genera, and iii) the PROB diet modified the gut microbiota of both GS and NGS fish, with a higher abundance of Kocuria and Bacillus genera, which reflected the establishment of the probiotic bacteria in the mucosal adherent surface, favouring long-term health promoting probiotic effects.AquaIMPACT (H2020 #818367), RYC2018-024049-I & ES