Nutritional value of torula yeast as an alternative protein feedstuff for hybrid Striped Bass (White Bass x Striped Bass)

ObjectiveTwo separate trials were conducted to evaluate the digestibility of a novel alternative ingredient, enhanced torula yeast (TY) Cyberlindnera jadinii, in diets for hybrid Striped Bass (HSB; White Bass Morone chrysops x Striped Bass M. saxatilis) and to evaluate graded inclusion levels of this product when replacing soybean products.MethodsIn trial 1, the digestibility of TY was determined by testing a reference diet and a TY diet (reference and TY ingredient at an 80:20 ratio). A total of 90 fish were fed the experimental digestibility diets for 21 days, and fecal samples were collected using the stripping technique. In trial 2, a comparative feeding trial evaluated the replacement of soybean meal by TY on a crude protein basis at 50, 100, 200, and 300 g of TY/kg of experimental diet. A total of 150 HSB (18.6 +/- 0.21 g/fish [mean + SE]) were distributed among fifteen 110-L glass aquaria. Each diet was fed to triplicate groups of fish for 9 weeks.ResultIn trial 1, apparent digestibility coefficients for protein, lipid, organic matter, and energy of TY were 0.97, 0.98, 0.75, and 0.75, respectively. The availability of essential amino acids also was generally high, ranging from 0.74 to 0.99. For trial 2, a second-order polynomial regression indicated that the optimal inclusion levels of TY in diets were 102, 112, and 109 g/kg for weight gain, feed efficiency, and protein conversion efficiency, respectively. However, the muscle yield linearly decreased with the graded inclusion levels of TY. Linear increases in intraperitoneal fat, hepatosomatic index, and whole-body lipid were observed as the inclusion of TY increased in the diet.ConclusionIn conclusion, nutrients from TY were well utilized by HSB, and it can replace soybean products without affecting growth performance, with the optimal TY inclusion level being 102-112 g/kg of diet. There is an increasing demand for environmentally friendly and cost-effective alternative feed ingredients because of many fish species produced in intensive aquaculture requiring high-quality protein ingredients. This study evaluated a torula yeast product that can be grown on complex carbohydrates derived from the wood industry, thereby converting low-value substrates to a high-quality protein ingredient. Based on results from separate digestibility and comparative feeding trials, nutrients from TY were well utilized by hybrid Striped Bass and the torula yeast product could replace soybean products without affecting growth performance, with the optimal inclusion level of 102-112 g per kg of diet.Impact statement