Effects of maturation, polyploidy, and nutrition on growth, composition, and gene expression within fatty acid metabolism in rainbow trout

In many cultured fish species, such as salmonids, gonadal development occurs at the expense of stored energy and nutrients, including lipids. Mobilization of intramuscular lipid during gonadal development decreases fillet quality. The aquaculture industry induces triploidy to generate sterile individuals; however, differences in lipid metabolism of female diploid (2N) and triploid (3N) trout may alter fillet quality. In addition, there is concern that genetic selection for increased growth negatively impacts fillet quality and muscle lipid content. Research in these areas would aid in the development of better management practices for efficient food-fish production that optimizes product quality.;The goal of this research is to assess the specific impacts of sexual maturation, polyploidy, and nutrition on growth responses, fillet quality attributes, and fatty acid content. Additionally, changes in gene expression of 35 genes within the regulatory pathways governing fatty acid metabolism of various energy stores were investigated to elucidate mechanisms regulating nutrient repartitioning during sexual maturation. Four studies were conducted to assess these variables. In the first study, effects of feeding level and polyploidy on fatty acid composition and metabolism of energy stores were considered. This study showed that ploidy had greater impact on fatty acid metabolism and composition of energy stores than moderately restricted diets at sexual maturation. A second study investigated changes in fatty acid metabolism of 2N and 3N female trout throughout sexual maturation. These data showed that there are no physiological differences between 2N and 3N females prior to 18 M of age; however, there are dramatic differences in energy store compositions and gene expression beginning at 20 M of age. In general, data indicate 2N fish have increased fatty acid beta-oxidation in white muscle that was associated with altered gene expression within the mTOR pathway and in visceral adipose tissue that was associated with increasedpparbeta expression. In contrast, increased expression of genes involved in fatty acid synthesis in 3N female liver appears to be associated with increased expression of PPARgamma as well as altered expression within the mTOR pathway, consistent with continued deposition of lipids in these fish. A subsequent study examined differences in fatty acid composition and gene expression between immature male and female rainbow trout. Females had higher muscle polyunsaturated fatty acid (PUFA) content; albeit, no differences were observed for other fatty acids measured. Gene expression data indicate possible increased fatty acid turnover in female trout muscle through increased expression of genes involved in both fatty acid synthesis and beta-oxidation. Male livers have higher expression of genes within beta-oxidation, which may contribute to the lower PUFA content. Lastly, to evaluate specific associations of fillet yield and fat content with differences in fatty acid metabolism, growth, fillet fatty acid composition, and gene expression were assessed for 100 fish chosen based on fillet yields and fat contents. This study indicated that high-yield/low-fat fish produced the highest quality fillets as measured by instrumental texture and composition. In addition, high-yield/low-fat fillets had the greatest long-chain, polyunsaturated fatty acid content. Overall, data suggests that differences in growth and fillet quality phenotypes may partially result from variation in the capacity for fatty acid, beta-oxidation through altered gene expression within the mTOR signaling pathway.;In general, sexual maturation, triploidy, and gender have profound affects on fatty acid composition, metabolism, and gene expression. Furthermore, the mTOR and PPAR signaling pathways have altered gene expression that is associated with differences in fatty acid composition and metabolism in rainbow trout