Live Yeast (Saccharomyces cerevisiae var. boulardii) Supplementation in a European Sea Bass (Dicentrarchus labrax) Diet: Effects on the Growth and Immune Response Parameters

Simple Summary: In animal science, dietary supplementation with probiotics offers several advantages, in terms of both environmental sustainability and production, and probiotic supplementation in aquatic animals is known to enhance stress tolerance, disease prevention, and growth, as has already been documented for several fish species. Among the various probiotics, the yeast-based ones have been stimulating a great deal of interest because of their ability to produce polyamines, which participate in numerous biological processes, and Saccharomyces cerevisiae var. boulardii (LSB), one of the most studied yeasts, has been used throughout the world for the prevention and treatment of a variety of gut inflammatory diseases. In our study, in order to obtain insights into the potential beneficial effects of this yeast as a probiotic, the dietary inclusion of an LSB strain (CNCM I-1079) was evaluated, at increasing concentrations (0, 100, and 300 mg kg(-1) of feed) for 90 days, on the welfare and health status of juvenile European sea bass, an important fish species in Mediterranean aquaculture. Our results indicate that LSB has an immunomodulatory action, and the observed lowering of pro-inflammatory gene transcripts in the gut suggests a possible anti-inflammatory action of this probiotic strain on the gut immune system of sea bass, with a possible enhancement of fish disease prevention. LSB also exerted a low, albeit insignificant, stimulating effect on the hematological and immunological parameters. The present study has been aimed at evaluating the effects of the dietary inclusion of the live yeasts, Saccharomyces cerevisiae var. boulardii (LSB) administered at increasing concentrations (0, 100, and 300 mg kg(-1) of feed, here referred to as LSB 0, 100, 300) for 90 days, on the health conditions of European sea bass. The main zootechnical parameters, histological and morphological analyses, innate immunity response parameters (intestinal cytokine expression, lysozyme content, spontaneous hemolytic and hemagglutinating activities, antibacterial activities, and peroxidase activity) were measured as fish welfare parameters. LSB did not impair either growth parameters or the morphometric indexes. LSB down-regulated interleukin-1 beta transcription in the distal gut of fish treated with 5.4 x 10(5) CFU g(-1) (LSB100) for 21 days. The interleukin-6 mRNA level decreased significantly in the proximal gut for both doses of yeast, after 21 days of feeding; the gene expression of interleukin-6 was significantly lower in the sea bass fed 10.81 x 10(5) CFU g(-1 )(LSB300) probiotic. The levels of TNF-alpha mRNA were not influenced by probiotic supplementation. Increases, although not significant, in the hematological and immunological parameters were also recorded. The data collected in the present study suggests that an LSB-supplemented diet acts on the gut immune system of sea bass by modulating the expression of the key inflammatory genes.