A novel fish meal-free diet formulation supports proper growth and does not impair intestinal parasite susceptibility in gilthead sea bream (Sparus aurata) with a reshape of gut microbiota and tissue-specific gene expression patterns

Abstract

The exponential growth of the aquaculture sector requires the development of sustainable aquafeeds with less dependence on marine products. The maximized replacement of fish meal (FM) and fish oil (FO) with plant ingredients has been extensively studied in the economically important species gilthead sea bream (Sparus aurata). Recently, major progress has been done with other alternative raw materials, though some non-pathological inflammatory response persisted with feed formulations that increased the circularity of resource utilization. In the present study, we evaluated the effects on growth performance, gene expression, intestinal microbiota and disease resistance of a FM-free diet (NoPAP SANA), based on plant ingredients, aquaculture by-products, algae oil, insect meal and bacterial fermentation biomasses as main dietary oil and protein sources, and supplemented with a commercially available health-promoting feed additive (SANACORE®GM). Juveniles of 21 g initial body weight were fed control or NoPAP SANA diets for 34 days, and head kidney, liver and posterior intestine were collected for gene expression analyses using customized PCR-arrays. Each tissue-specific PCR covered 96 genes in total and included markers of growth performance, lipid and energy metabolism, antioxidant defence, immune system, and intestinal function and integrity. From the same fish, the adherent bacteria of the posterior intestine were studied by Illumina sequencing of the V3-V4 region of the 16S rRNA. The remaining fish were challenged with the intestinal parasite Enteromyxum leei for 78 days and sampled for parasite diagnosis. Both control and NoPAP SANA fish grew efficiently considering gilthead sea bream standards. Before parasite challenge, the NoPAP SANA group showed differential expression of 17, 2 and 4 genes in liver, head kidney and posterior intestine, respectively. The intestinal bacterial composition showed no major differences in diversity or at the phylum level. However, 29 abundant OTUs significantly changed with the diet. From these, 10 OTUs were significantly correlated with differentially expressed genes in the different target tissues. Inferred metagenome analyses revealed that the altered microbiota with NoPAP SANA diet could account for changes in 15 metabolic pathways. The intensity and prevalence of infection after the parasite challenge did not significantly vary between dietary treatments, and infected fish from both groups showed similar disease outcome. Altogether, these results indicate that the NoPAP SANA diet promoted optimal growth and a healthy condition in gilthead sea bream without affecting susceptibility against the tested intestinal parasite, as often observed with alternative diets following current industry formulations.