Date of Award
Master of Science
Numerous alternatives to fish meal (FM) have been investigated by aquaculture nutritionists in order to reduce aquacultures reliance on this finite and costly resource. Traditional protein alternatives derived from terrestrial plants and animals have shown varying success and limitations. In order to produce effective, least cost feeds new alternative proteins must be investigated. Ethanol yeast (EY), a co-product of bio-ethanol production may be a novel protein source. The increasing capacity of the bio-ethanol industries has made EY an increasingly available commodity. However, no studies have been done to evaluate ethanol yeast as a FM replacement in diets of carnivorous fish. Accordingly the objectives of this trial were to evaluate the suitability of EY as a FM alternative in aquafeeds in terms of production performance of sunshine bass. Then based on the results of the first feeding trial, identify any limitations to increased implementation of EY and undesirable effects on physiological robustness of sunshine bass. The first feeding trial using feeds in which EY replaced 0%, 25%, 50%, 75% and 100% of the FM protein from a 30% FM basal diet found that up to 75% of the FM protein could be replaced without significant effects on production performance. Fish reared on the 15% FM treatment (50% replacement) exhibited significantly higher weight gain than the control treatment (30% FM). Low intake in the complete replacement treatment (0% FM) indicated poor palatability. A second trial was conducted using the 15%, 7.5% and 0% FM treatments (50%, 75% and 100% replacement levels respectively), with and without the addition of a palatant in an effort to increase intake. A stress challenge was conducted at the end of the trial to measure dietary effects on physiological robustness. Production performance followed the same trends as the first trial with the 15% FM and 7.5% FM treatments being similar. Whole carcass composition was significantly affected by increasing EY inclusion. Unlike the first trial survival for the 0% FM treatments was significantly affected during the second trial, with an increase in cannibalism and starve outs being noted. Dietary inclusion of EY had no significant effects on hematology before or after stress. Stress however, did significantly affect glucose and lysozyme levels. Cortisol was uncharacteristically high in unstressed fish. Further studies are needed to better determine utilization and digestibility of EY based feeds as well as their effects on hematology at rest and after stress. Based on the results of this study however, the optimal FM inclusion level in EY based feeds is between 75 g/kg and 150g/kg.
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