Replacement of Fish Meal with Ethanol Yeast in the Diets of Sunshine Bass

Increasing demand and rising costs of fish meal (FM) coupled with static landings of reduction fisheries have made continued use of FM-rich aquaculture feeds environmentally and economically unsustainable. Animal- and plant-derived proteins have been investigated as alternatives to FM, with variable success. Observed limitations of commonly used alternative proteins have led nutritionists to investigate new alternatives to FM. Ethanol yeast, a co-product of bioethanol production and potential new alternative protein source, was evaluated as a FM replacement in the diets of sunshine bass (female white bass Morone chrysops x male striped bass M. saxatilis). Five diets were evaluated, including a control diet containing 30% FM and four experimental diets (22.5, 15, 7.5, and 0% FM) in which 25, 50, 75, or 100% of the FM content was replaced with ethanol yeast. Juvenile sunshine bass (16 g) were fed twice daily to apparent satiation for 45 d. Production performance of sunshine bass was not impaired by partial FM replacement and in some cases was marginally improved by dietary inclusion of ethanol yeast. Feed conversion ratio, specific growth rate, and feed intake were equivalent among fish fed the control, 22.5% FM, 15% FM, and 7.5% FM feeds; weight gain was significantly increased in the 15% FM group compared with the control. However, complete replacement (0% FM) resulted in significantly impaired growth performance and conversion efficiency. Whole-body composition did not differ with respect to moisture, ash, or protein content; however, crude lipid content was significantly elevated in the 7.5% FM treatment, suggesting a protein-energy imbalance in this formulation. Although our study was a short-term screening trial, based on our results we suggest that an optimal level of FM in ethanol-yeast-based feeds for sunshine bass would be between 7.5% and 15%.