Date of Award
Master of Science
Traditionally, the aquaculture industry has utilized fish oil in aquafeeds as a source of energy and n-3 long-chain polyunsaturated fatty acids (LC-PUFA). Use of fish oil has the added benefit of increasing the n-3 LC-PUFA content of farmed fish, increasing its nutritional value to human consumers. Aquaculture continues to rely heavily on reduction fisheries and fish oil as the only economically viable source of n-3 LC-PUFA, however this practice is arguably unsustainable. In order to meet growing demand for fish and its associated health benefits, aquafeed ingredients and feeding strategies that yield equivalent production performance and edible product fatty acid (FA) profile must be developed. My goal was to screen a range of plant oils as alternatives to fish oil in feeds for hybrid Striped Bass Morone chrysops x M. saxatilis (objective 1), and then assess the optimal alternative oil in the context of graded fish oil sparing and implementation of finishing as a strategy to augment fillet n-3 LC-PUFA content prior to harvest. In objective 1, production performance and fillet FA profile were evaluated in juvenile hybrid Striped Bass (67.8 ± 0.2 g, mean ± SE) fed practical feeds (40% protein, 15% lipid) containing fish oil (FO) or 50/50 blends of fish oil and standard (STD SO), saturated fatty acid (SFA)-enriched (SFA SO), low alpha-linolenic acid (LO ALA SO), or monounsaturated fatty acid (MUFA)-enriched (MUFA SO) soy oil. Feeds were offered to quadruplicate tanks of fish (8 fish/tank, 67.8 ± 0.2 g) in a water reuse system for 12 weeks. Production performance was largely unaffected by dietary treatment. No significant differences were observed in weight gain (214 ± 5%) or specific growth rate (1.4 ± 0.0% body weight/day) among treatments. Some differences were observed in feed conversion ratio among SO-fed treatments; however, these treatments were not significantly different from the FO control (1.2 ± 0.0). Fillet fatty acid composition was generally observed to reflect dietary fatty acid composition and intake. The STD SO and LO ALA SO diets resulted in a significant decrease in LC-PUFA content and substantial increases in medium-chain polyunsaturated fatty acids (MC-PUFA) and n-6 fatty acids within the fillet. Both the SFA SO and MUFA-SO diets resulted in fillet LC-PUFA levels similar to the FO diet; however, the MUFA-SO feed yielded significantly elevated levels of MUFA. Of the alternative oils evaluated, all would be acceptable as partial substitutes for fish oil in terms of production performance, though the SFA SO appeared to be the most suitable in terms of both production performance and maintaining a fatty acid profile similar to that associated with feeding fish oil. The goal of objective 2 was to further evaluate the SFA-enriched soy oil at graded levels of fish oil sparing in grow-out diets fed in conjunction with finishing with a fish oil-based feed for different durations prior to harvest. Quadruplicate tanks of fish (8 fish/tank, 110.6 ± 0.4 g) were fed experimental diets in which 50, 75, or 100% of the dietary fish oil was replaced with SFA-enriched soy oil in conjunction with 4, 8, or 12 weeks of finishing with a 100% fish oil feed (10 feeding regimens total) for 21 weeks. Significant differences in growth performance were found among the feeding regimens evaluated in this experiment. Final individual weight was significantly different between treatments with the 50-SFA-SO + 8 weeks and 100-SFA-SO + 12 weeks, but none of the treatments was significantly different from the 100-FO control; when expressed in terms of percent weight gain, growth did not vary significantly among treatments. FCR varied significantly among feeding regimens, with the lower values generally associated with regimens receiving greater amounts of fish oil; more specifically, FCR values were significantly elevated among all three 100-SFA compared to the 100-FO control (1.4-1.5 vs. 1.2). Furthermore, treatments providing the least amount of fish oil exhibited increased levels of MUFA, MC-PUFA and n-6 FA. Finishing significantly affected fillet fatty acid profile, with longer finishing periods generally resulting in more comprehensive fillet modification, effectively reversing the deviations associated with feeding the SFA-enriched soy oil. My results indicate that fish oil can be replaced with SFA-SO at 50% and 75% with minimal effects on both growth performance and fillet FA. Although substantial amounts of fish oil may still be needed in concurrence with SFA-SO in order to provide ideal FA composition in fillets, any significant reduction in fish oil may be useful in further alleviating the oceans finite resources as well as decreasing production costs for the aquaculture industry.
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