Use of Metabolically Modified Canola Oil as a Replacement for Fish Oil in Practical Diets of Pacific White Shrimp Litopeneaus vannamei
Type of DegreeMaster's Thesis
School of Fisheries, Aquaculture, and Aquatic Sciences
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The rapid growth of the aquaculture sector can be stifled by the inadequate supply of fish oil, leading the sector to search for alternative oil sources. The efficacy of metabolically modified canola oil (MCO) has not been extensively tested in shrimp. Hence, the objective of this research was to quantify the effect of MCO on shrimp growth performance at various menhaden fish oil (FO) and menhaden fishmeal (FM) replacement levels. FO was replaced by MCO, while FM was replaced by poultry meal (PM). Ten diets were formulated to contain 8% lipid and 36% protein with varying levels of fish oil and tested in both clear and green water tank systems. In the first experiment, all ten diets were evaluated under clear water conditions using indoor glass aquaria. Results indicated shrimp reared on treatments with above 90% FO replacement had significantly lower (p<0.05) growth and feed utilization likely due to a nutritional deficiency of long chain highly unsaturated fatty acid (LC-HUFA), docosahexaenoic acid (DHA). In the second experiment, five experimental diets were utilized in a green water growth trial, with FO replacement levels from 75% to 95%. At conclusion, no significant differences were observed between treatments that indicated an effect of treatment on shrimp growth and survival, suggesting that all replacement levels were successful. Shrimp tissues from both experiments were analyzed for fatty acid (FA) profiles. Lipid results indicated that the diets containing 90% FO replacement or higher in the clear water trial were very close to the nutritional LC-HUFA requirement but were deficient in DHA. Significant differences in shrimp growth were observed in the clear water growth trial, but not in the green water growth trial. This difference could possibly be attributed to the consumption of algae from the system, supplementing the contribution from the diets and meeting nutritional requirement for limiting fatty acids like DHA. Whole shrimp were kept from the green water growth trial to be used for human sensory analysis. Cooked shrimp samples were evaluated on appearance, juciness, texture, flavor, and overall acceptability. Shrimp fed FM-MCO received consistent complaints of less desirable texture, but there were no significant differences between sensory parameters. Diets FM-FO, FM-MCO, PM-FO, and PM-MCO were used for a shrimp palatability trial to determine if growth differences could be attributed to poor palatability of MCO or PM. No significant differences were observed in amount of feed consumed by the shrimp, indicating that all diets were equally palatable. Results of this research confirm that albeit MCO has sufficient DHA as a pure oil source, the dilution effect of native oils results in the 100% replacement being deficient in DHA. MCO is not yet suitable to fully replace fish oil in shrimp diets, but is able to be replaced at levels up to 90% without large sacrifices in growth and survival. Because results from these experiments are conflicting, more research with this product is warranted. Further experiments in green water conditions should evaluate the lipid profile of shrimp that are not fed any feed in order to determine how much of the EFA nutritional requirement is fulfilled by the natural foods present in green water systems.