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ARS Home » Northeast Area » Leetown, West Virginia » Cool and Cold Water Aquaculture Research » Research » Publications at this Location » Publication #308890
Title: Effects of feeding level and sexual maturation on fatty acid metabolism gene expression in muscle, liver, and visceral adipose tissue of diploid and triploid rainbow trout, Oncorhynchus mykiss

Author
item MANOR, MEGHAN - West Virginia University
item Cleveland, Beth
item Weber, Gregory - Greg
item KENNEY, P. BRETT - West Virginia University

Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2014
Publication Date: 9/19/2014
Citation: Manor, M.L., Cleveland, B.M., Weber, G.M., Kenney, P. 2014. Effects of feeding level and sexual maturation on fatty acid metabolism gene expression in muscle, liver, and visceral adipose tissue of diploid and triploid rainbow trout, Oncorhynchus mykiss. Comparative Biochemistry and Physiology. 179:17-26.

Interpretive Summary: In many cultured fish species, such as salmonids, gonadal development occurs at the expense of stored energy and nutrients, including lipids. As a part of this repartitioning of nutrients, the quality of the fillet is decreased so that nutrients including omega-3 fatty acids, can be deposited into the eggs. Thus, these events are important to hatcheries interested in producing high quality eggs, and producers of large fish who are interested in the production of high quality fillets. However, mechanisms regulating this nutrient repartitioning during sexual maturation are not well understood. We investigated effects of ration level and sexual maturation on expression of 35 genes involved in fatty acid metabolism. Gene expression profiles were assessed in liver, white muscle, and visceral adipose tissue of sexually maturing, normal diploid female rainbow trout fed low, medium, and high amounts of feed. Additionally, triploid female trout which have three sets of chromosomes instead of two sets as in normal diploid fish, were fed at the medium ration for comparison to diploid females fed at the same ration. Triploids are sterile and do not grow large ovaries and therefore do not need to repartition nutrients. Gene expression was affected by ration level only in white muscle. On the other hand, sexual maturation affected gene expression across all three tissue types, indicating enhanced fatty acid mobilization within all three tissues during sexual maturation. Furthermore, increased gene expression across ration levels in diploid compared with triploid females suggests that maturation-associated hormonal signals, such as the sex steroid estrogen, may regulate these effects. This information can be used by rainbow trout producers to determine when to harvest large food-fish before maturation affects fillet quality, and provides information that can assist development of diet formulations or feeding strategies to maximize fillet or egg quality.

Technical Abstract: In many cultured fish species, such as salmonids, gonadal development occurs at the expense of stored energy and nutrients, including lipids. However, mechanisms regulating nutrient repartitioning during sexual maturation are not well understood. This study investigated effects of ration level and sexual maturation on expression of 35 genes involved in fatty acid metabolism, including genes within fatty acid synthesis, beta-oxidation, and cofactors of the mTOR and PPAR signaling pathways. Gene expression profiles were assessed in liver, white muscle, and visceral adipose tissue of sexually maturing, diploid (2N) female rainbow trout fed at 0.25 and 0.50% of tank biomass/day and to apparent satiation. Additionally, sterile triploid (3N) female trout were fed at 0.50% of tank biomass/day for comparison to 2N females fed at the same ration level. Gene expression was affected by ration level only in white muscle; erk and acat2 were increased in fish fed higher rations. On the other hand, sexual maturation affected gene expression across all three tissue types. Data indicate 2N fish have increased expression of beta-oxidation genes within white muscle and within visceral adipose tissue. These findings support enhanced fatty acid mobilization within these tissues during sexual maturation. Increased expression of fatty acid synthesis genes in 3N female liver is associated with increased expression of mTOR cofactors and ppar-gama, which reflects continued deposition of lipids in these fish. Furthermore, increased expression of genes involved in beta-oxidation pathways across ration levels in 2N females suggests that maturation-associated hormonal signals, such as estrogen, may regulate these effects.