Date of Award
Master of Science
The aquaculture industry is expanding to supply the demand for sustainable protein, essential nutrients, and energy. Recent reports of worldwide fish production indicate a rise in aquaculture, coupled with near static capture fishery landings. Feed prices represent a major limiting factor for aquaculture as ingredients sourced from wild caught fisheries remains stagnant. Fish oil is included in the realm of expensive, marine sourced ingredients and is a highly nutritious commodity. Lipids are indispensable constituents of aquafeeds because they provide essential energy and nutrients. Some fatty acids are deemed essential because they must be obtained via dietary intake to avoid pathology and ultimately mortality. Depending upon the species, essential fatty acids may include C18 polyunsaturated fatty acids (C18 PUFA) or long chain polyunsaturated fatty acids (LC-PUFA). Despite many years of research, essential fatty acids requirements in aquaculture nutrition are still not fully understood. Therefore, the work described herein was intended to determine the essentiality of C18 PUFA or LC-PUFA (including n-3 and n-6 fatty acids) in diets of hybrid Striped Bass and Rainbow Trout through survival, growth performance, and fatty acid tissue analysis. The essentiality in the two taxa were examined through feeding fish experimental diets that met all other nutrient requirements, except for fatty acid nutrition, for a period of 8 weeks. Diets were created to isolate individual fatty acids with hydrogenated soybean oil, rich in saturated fatty acids (SFA), and the absence or addition of various C18 PUFA or LC-PUFA fatty acid concentrates. An ideal fatty acid nutrition diet was formulated with 100% fish oil. Hybrid Striped Bass are reported to require EPA (eicosapentaenoic acid, 20:5n-3) and/or DHA (docosahexanoic acid, 22:6n-3) at 0.5-1% dietary inclusion rate. For all vertebrates, ARA (arachidonic acid, 20:4n-6) may also be important when determining LC-PUFA requirements. Results of this study indicate that hybrid Striped Bass do have a dietary requirement for LC-PUFA and that provision of C18 PUFA alone is insufficient to avoid essential fatty acid deficiency and support optimal growth of this fish. Existing fatty acid requirements for Rainbow Trout are 0.7 – 1.0% 18:3n-3 (alpha linolenic acid, ALA) and/or 0.4 – 0.5% n-3 LC-PUFA. It is debated whether Rainbow Trout require C18PUFA or LC-PUFA. Results of this study indicate Rainbow Trout are physiologically able to synthesize LC-PUFA from C18PUFA. Therefore, Rainbow Trout do not require LC-PUFA-rich feeds, but providing preformed LC-PUFA in the diet may be energetically advantageous and support improved growth performance. Quantitatively assessing essential fatty acid requirements in representative finfish will allow for more accurate formulations, but aquaculture is incredibly diverse and it will not be possible to conduct requirement students in all cultured taxa. The traditional formulation conventions for fatty acid requirements failed to recognize that the cold-water and marine species that had been evaluated were largely top-level carnivores, whereas the warm-water and freshwater species were largely herbivores, omnivores, or low level carnivores. In more recent work, the use of trophic levels to predict and generalize essential fatty acid requirements is gaining credence. Utilizing the trophic hierarchy ideology to guide EFA requirements may provide more accurate formulation. However, more research on various taxa is needed to determine the exact threshold at which PUFA essentiality, specifically requirements for C18 PUFA vs. LC-PUFA, can be predicted.
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