Effects of sexual maturation and feeding level on fatty acid metabolism gene expression in muscle, liver, and visceral adipose tissue of diploid and triploid rainbow trout, Oncorhynchus mykiss

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 compared sexually maturing diploid (2 N) and sterile triploid (3 N) female rainbow trout to investigate effects of sexual maturation on expression of 35 genes involved in fatty acid metabolism, including genes within fatty acid synthesis, β-oxidation, and cofactors of the mTOR and PPAR signaling pathways, in liver, white muscle, and visceral adipose tissue. Diploid fish were fed at different rations (0.25% and 0.50% tank biomass, and satiation) to determine effects of ration on gene expression. Gene expression was affected by ration level only in white muscle; erk and acat2 had higher expression in fish fed higher rations. On the other hand, sexual maturation affected gene expression across all three tissue types. Data indicate 2 N fish have higher expression of β-oxidation genes within white muscle and within visceral adipose tissue. These findings support enhanced fatty acid mobilization within these tissues during sexual maturation. Higher expression of fatty acid synthesis genes in 3 N female liver is associated with higher expression of mTOR cofactors and pparγ, which reflects continued deposition of lipids in these fish. Furthermore, greater expression of genes involved in β-oxidation pathways across ration levels in 2 N females suggests that sexual maturation and the associated maturation-related signals are stronger regulators of lipid metabolism-related genes rather the rations applied in the current study.