Aqualase®, a yeast-based in-feed probiotic, modulates intestinal microbiota, immunity and growth of rainbow trout Oncorhynchus mykiss

Yeast probiotics have great promise, yet they received little attention in fish. This study investigated the influence of Aqualase((R)), a yeast-based commercial probiotic composed of Saccharomyces cerevisiae and Saccharomyces elipsoedas, on health and performance of rainbow trout (Oncorhynchus mykiss). Probiotics were incorporated in the diets at three different inclusion levels (1%, 1.5% and 2%) and administered to the fish for a period of 8 weeks. After the feeding trial, intestinal total viable aerobic bacterial count was significantly higher in fish group that received 2% in-feed probiotics. In addition, a significant increase in at least 11% in intestinal lactic acid bacteria population was observed in all probiotic-fed groups. Total protein level and lysozyme activity in skin mucus were significantly elevated following probiotic feeding. Inhibitory potential of skin mucus against fish pathogens was significantly enhanced by at least 50% in probiotic-fed groups. Humoral and cellular immune parameters were influenced by probiotic feeding and the effects were dependent on inclusion level. Digestive physiology was affected by infeed probiotics through improvement of intestinal enzyme activities. All growth performance parameters were significantly improved following probiotic administration specifically at inclusion rate 1.5% and above. Taken together, the results revealed that Aqualase((R)) is a promising yeast-based probiotic for rainbow trout with the capability of modulating the intestinal microbiota, immunity and growth.