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Effects of dietary canola oil level on growth, fatty acid metabolism and physiology of red sea bream fingerlings and spring chinook salmon parr Huang, Shih-Yin Susie

Abstract

Lipids are an invaluable dietary component for fish because they furnish the indispensable essential fatty acids (EFA) that are required for normal growth and development of the animal EFA generally refers to 18:3n-3, 18:2n-6 and their metabolic derivatives, 20:5n-3, 22:6n-3 and 20:4n-6. Marine and freshwater species have distinct EFA requirements largely due to differences in the lipid compositions of their naturally available diets as well as differences in their metabolism of lipids and fatty acids (FA). Nonetheless, marine fish oils (FO) are the traditional lipid sources for finfish aquafeeds in both the marine and freshwater environments. However, recent environmental and economical constraints have generated interest in non-marine sources of lipid in finfish aquafeeds. This thesis examined the physiological effects of partially substituting canola oil (CO) for FO in practical commercial diets of two high-value finfish species during their early development. In the first experiment, triplicate groups of red sea bream fingerlings (Pagrus major) were fed 4 soenergetic, isonitrogenous and isolipid commercial diets with varying levels of refined CO up to 70% of total dietary lipid content over a 12-week period. In the second experiment, triplicate groups of spring chinook salmon parr (Oncorhynchus tshawytscha) were fed practical dry diets in which CO comprised up to 72% of total lipid (mostly FO) over a 30-week period. No adverse effects of diet on growth and whole body proximate constituents were found in either study. Whole body FA composition correlated strongly to the diet FA compositions. Signs of specific FA retention were observed in both species, but to a much greater degree in the spring Chinook salmon. Nonetheless, specific FA were strongly retained in the red sea bream liver polar lipids. Ionoregulatory development in the spring chinook salmon was uncompromised by diet treatment. However, whole body [Cl⁻] was influenced by diet at week 10 and 15, where body [Cl⁻] was - negatively correlated to dietary CO content. Overall, results demonstrated excellent potential for CO to be the main source of supplemental lipid in commercial aquafeeds for juvenile Japanese red sea bream and spring chinook salmon parr.

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