Effects of selenium-enriched prebiotic on the growth performance, innate immune response, oxidative enzyme activity and microbiome of rainbow trout (Oncorhynchus mykiss)

Abstract

Using prebiotics as functional ingredients in aquafeed is an emerging approach to prevent disease and improve fish production. This study explored the effect of supplementing aquafeed with selenium-enriched prebiotic on the growth performance, plasma lysozyme activity, and oxidative enzymes activities of various tissues of the rainbow trout, Oncorhynchus mykiss. The fish scale and intestinal microbiomes were also characterized. A genetically- modified, whole-cell inactivated Schizosaccharomyces pombe that produces a novel form of selenium called selenoneine was used as a prebiotic supplement in this study. Selenoneine is a novel selenium-containing molecule with an antioxidant activity, suggesting it has potential to improve the production of fish when used as a functional ingredient in aquafeeds. To investigate if this selenium-enriched S. pombe can strengthen the production metrics, modulate the surface and internal microbiome, and improve the health status of fish, an 8-week fish feeding trial was conducted. A commercial feed was supplemented with no addition (control), 5 g Kg−1 (0.5%), or 10 g Kg−1 (1.0%) of selenium-enriched S. pombe. Fish were harvested at the middle (week 4) and end of the trial (week 8). There were no significant differences (p > 0.05) in food conversion ratio, condition factor, or survival of fish during the trial. The microbiome also remained stable during the experiment. No effect (p > 0.05) was observed in the growth performance of the fish at week 4; however, at week 8 fish that were fed 0.5% yeast had a significantly higher weight gain (p < 0.05), hepatosomatic index, and viscerosomatic index than the fish fed control and 1.0% diets. At week 4, the concentration of plasma lysozyme in fish fed 0.5% yeast was significantly higher (p < 0.05) than the control fish and fish fed the 1.0% diet. No significant differences (p > 0.05) were observed in glutathione peroxidase activity in the liver, kidney, or plasma of fish fed experimental diets at the two different sampling times. However, the superoxide dismutase activity of plasma was significantly higher with the 0.5% diet than the control and 1.0% fed fish at week 4. At week 8, both the 0.5% and 1.0% diets led to significant increases (p < 0.05) in superoxide dismutase activity in the plasma of fish when compared to the control diet. This study demonstrates that supplementation of aquafeed with selenoneine-producing S. pombe can improve the growth, immune response, and oxidative status of fish. Thus, this ingredient holds a promising potential to enhance sustainability within the aquaculture industry.