Comparative transcriptomics and metabolomics reveal specific biochemical responses in cultured largemouth bass (Micropterus salmoides) juveniles with sexual dimorphism

Currently, it has been well established that growth, bodily form, physiological responses, and metabolic features of teleost fish may display sexual difference during intensive farming. Herein, the study aims to mainly examine the disparities of histomorphological and molecular responses in representative tissues liver and caudal vein blood from male and female cultured largemouth bass (Micropterus salmoides) juveniles by tracking a growth period of 135 days for reaching sexual maturity. The liver indices of a majority of the females, such as mass ratio of hepatic and visceral tissues (MRHV), hepatosomatic index (HSI), and hepatic lipid droplet abundance, were obviously greater than the males. Observational outcomes on size and distribution of accumulated lipid droplets in the liver of the females were more obvious and distinct from the males. Hepatic transcriptome sequencing results also demonstrated that glycerophospholipid metabolism-related/lipid transport-related genes (e.g. chkb, vtg3), PPAR signaling pathway, and aromatic amino acids metabolism (e.g. tyrosine, phenylalanine) were more active in the females; whereas, genes or pathways related to long-chain lipid transport (e.g. slc27a6), fatty acid biosynthesis and decomposition (e.g. ptgdsa), tryptophan metabolism, and immunological/inflammatory responses (e.g. mst1), as well as mTOR/PI3K-Akt/FoxO/AMPK signaling pathways in the males, were more evidently up-regulated than the females. Serum non-targeted metabolomics results exhibited that 5-hydroxyindoleacetic acid (growth factor derivative) and adipoyl-l-carnitine (lipid transporter) in the males were higher in quantity while L-kynurenine (tryptophan metabolism) and l-carnitine (lipid transporter) in the females higher than the males. The findings preliminarily showed that activity of PPAR signaling pathway and high expression of chkb gene might be crucial mechanisms in gained hepatic lipids in the females, while the actions of metabolites l-carnitine/adipoyl-l-carnitine might be more conducive to lipid transport in the liver of the males.