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Title: Differences in growth, fillet quality, and fatty acid metabolism-related gene expression between juvenile male and female rainbow trout

Author
item MANOR, MEGHAN - West Virginia University
item Cleveland, Beth
item KENNEY, P. BRETT - West Virginia University
item Leeds, Timothy - Tim

Submitted to: Fish Physiology and Biochemistry Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2015
Publication Date: 3/19/2015
Citation: Manor, M.L., Cleveland, B.M., Kenney, P., Leeds, T.D. 2015. Differences in growth, fillet quality, and fatty acid metabolism-related gene expression between juvenile male and female rainbow trout. Fish Physiology and Biochemistry Journal. 41(2):533-547.

Interpretive Summary: Much of what is known in rainbow trout regarding differences between male and female fish is collected after the fish begin to sexually mature, a process that begins at 1.5 yr of age and negatively affects fillet quality. Most trout are harvested as food fish between 1-1.5 yr of age, prior to when sexual maturation begins, and it is unknown if attributes of fillet quality differ between male and female fish at this time. Male and female rainbow trout were harvested at 14 months of age, and analyzed for growth, fillet quality, lipid profile, and expression of genes related to lipid metabolism. Female fish produced firmer fillets with greater fillet yield. Differences in lipid profiles were evident between the sexes, as were expression of lipid metabolism-related genes. These findings indicate that there are differences in economically important traits between harvest age male and female rainbow trout, and from a production standpoint these differences tend to favor the female. Therefore, management decisions like production of all-female fish is advantageous not only to avoid the problem of early-maturing males (fish that sexually mature at 1 yr), but because the females appear to produce a better fillet.

Technical Abstract: Sexual maturation occurs at the expense of stored energy and nutrients, including lipids; however, little is known regarding gender effects on nutrient regulatory mechanisms in rainbow trout prior to maturity. Thirty-two, 14 month old, male and female rainbow trout were sampled for growth, carcass yield, fillet composition, and gene expression of the liver, white muscle, and visceral adipose tissue. Growth parameters, including gonadosomatic index, were not affected by gender. Females had higher percent separable muscle yield, but there were no gender effects on fillet proximate composition. Fillet shear force indicates that females produce firmer fillets than males. Male livers had greater expression of rictor, suggesting increased mTOR signaling through TORC2. In addition, male livers demonstrated increased expression of ppar', with subsequent increases in expression of lipoprotein lipase and malic enzyme genes, which are transcriptionally regulated by ppar'. Male liver also exhibits increased cpt1b expression while females have increased expression of cpt1a in the liver and cpt1d and cpt2 in white muscle. These findings are indicative of increased mitochondrial ß-oxidation through differential regulation of carnitine palmitoyltransferase isoforms. Compared to males, females exhibited increased expression of raptor in white muscle, suggesting increased signaling through TORC1, which is supported by higher expression levels of srebp1, a gene regulated by TORC1 signaling. Overall, data suggests that there is differential regulation of gene expression in male and female rainbow trout tissues prior to onset of sexual maturity causing repartitioning of nutrients during maturation. These changes are primarily within the mTOR and PPAR' pathways.