Dietary arachidonic acid differentially regulates the gonadal steroidogenesis in the marine teleost, tongue sole (Cynoglossus semilaevis), depending on fish gender and maturation stage

Abstract

A 3-month feeding trial with tongue sole Cynoglossus semilaevis broodstock was conducted before and during the spawning season to investigate the effects of dietary arachidonic acid (ARA) on the production of sex steroid hormones and gonadal gene expression of key proteins in steroidogenesis. Three isonitrogenous and isolipidic experimental diets were formulated to contain different ARA levels: the control diet without ARA supplementation (C, 0.58% ARA of total fatty acids (TFA)) and two diets with low (5.14% of TFA, ARA-L) or high ARA (15.44% of TFA, ARA-H) supplementation. The diets were randomly assigned to 9 tanks of 3-year-old tongue sole (10 females and 15 males in each tank). Fish were reared in a flowing seawater system and fed to apparent satiation twice daily. At the end of the feeding trial, tissue samples from mature females (MF, with spontaneous ovulation), immature females (IMF, early vitellogenesis), and mature males (MM, expressing milt) were collected to assay the production of sex steroid hormones, gonadal gene expression of sex steroid-synthesizing proteins, as well as the fatty acid profiles of gonad, liver and muscle lipids. Results showed that ARA supplementation significantly reduced the estradiol production in females, but stimulated the testosterone production in males. ARA supplementation significantly reduced the mRNA expression of aromatase in ovaries but significantly increased the gene expression of 3β-hydroxysteroid dehydrogenase (3β-HSD) in testes. In mature ovaries, diet ARA-L significantly reduced the gene expression of follicle stimulating hormone receptor (FSHR), 3β-HSD, and 17β-HSD; however, in immature ovaries, it significantly increased the gene expression of FSHR, steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage enzyme (P450ssc), 3β-HSD, and 17β-HSD. In all gonads, 17α-hydroxylase (P450c17) responded to dietary ARA differently from other sex steroid-synthesizing proteins. ARA was preferentially accumulated in tongue sole gonad lipids. ARA concentrations were highest in gonad, liver and muscle lipids of MM fish and lowest in MF fish. Compared to female tongue sole, males had higher DHA concentrations in gonad lipids, but lower concentrations in liver lipids. In conclusion, results suggest dietary ARA regulates sex steroid hormone synthesis in tongue sole broodstock, and accumulates in gonad lipids, depending on both fish gender and maturation stage. Dietary ARA supplementation appears more important for male fish than for female fish, and more important for immature females than for mature females. Statement of relevanceThis study is beneficial to the broodstock diet formulation.