There is a continually growing interest in novel ingredients which can serve as alternatives to fisheries-derived proteins in aquaculture. The alternative ingredients that have been receiving more attention recently include insect meals and single cell proteins obtained from bacteria, algae, and yeasts. The inactivated dry yeast Saccharomyces cerevisiae product DY-Pro (Meridian Biotech, LLC) is produced using co-products of the dry mill corn ethanol fermentation process and holds great potential as an aquafeed ingredient. Although many dry yeast products have been evaluated as providers of various immunostimulating compounds in several aquaculture species, only a few studies have shown that dry yeast products may replace fishmeal in diets for aquatic organisms. Indeed, in a previous collaboration, graded replacement of 2 to 100% of fishmeal protein by DY-Pro did not significantly affect Nile tilapia’s weight gain or gut morphometric parameters, but linearly improved feed and nutrient utilization.
Farm-raised catfish is the largest aquaculture industry in the United States with production valued at approximately $400 million annually. Although fishmeal is typically not a major protein feedstuff in catfish diets, replacing it with alternative protein feedstuffs such as DY-Pro could contribute to reducing diet costs and sparing marine resources. Therefore, this study was conducted to investigate the effect of either partially or totally replacing fishmeal (included at 14.8% by weight in the control diet) by the inactivated dry yeast product DY-Pro. The DY-Pro replaced 0% (DY-PRO0), 5% (DY-PRO5), 25% (DY-PRO25), 50% (DY-PRO50), 75% (DY-PRO75) or 100% (DY-PRO100) of the protein provided by fishmeal in six isonitrogenous and isocaloric experimental diets. Each diet was fed to quadruplicate groups of the experimental fish (initial average body weight 39.4 ± 1.6 g) for 8 weeks.
At the end of the feeding trial, the graded replacement of 5 to 100% of fishmeal protein by the DY-Pro did not have any negative impacts on fish survival, fillet yield, hepatosomatic and viscerosomatic indices. However, as higher levels of DY-Pro were included in the experimental diets, weight gain and feed efficiency were progressively reduced. Broken-line regression analysis of weight gain data indicated that up to 21% of dietary protein contributed by fishmeal could be replaced with DY-Pro without significantly affecting growth performance and condition indices of channel catfish juveniles.