Effects of long-term sex steroid hormones (estradiol and testosterone)–supplemented feeds on the growth performance of Chinese tongue sole ( Cynoglossus semilaevis )

The phenomenon of sexual size dimorphism (SSD), existing in mammals, birds, reptiles, spiders, amphibians, insects, and fishes, is generally related to feeding efficiency, energy allocation, sex steroids, and somatotropic and reproductive endocrine axes. Recently, positive and negative regulations of sex steroids have been reported on SSD in various species. Chinese tongue soles ( Cynoglossus semilaevis ) at 4 months were fed with 17β-estradiol (E2) and testosterone (T) supplemented feeds for 8 months to assess the effect of sex steroids on growth traits in different sexes. The potential genetic regulation was examined using several growth-related genes. The results showed that two sex steroid hormones had inhibitory effects on the growth performance of different sexes of C. semilaevis . At the age of 8 months, the expression of insulin-like growth factor 2 gene ( igf2 ), 24-dehydrocholesterol reductase ( dhcr24 ), leptin , and estrogen receptor 2 ( esr2 ) in the liver showed an overall downward trend. The expression of insulin-like growth factor 1 ( igf1 ) was reduced, while thyroid hormone receptor-associated protein 3 ( thrap3 ) expression tended to increase in the gonad after T and E2 treatments. In the brain, somatostatin 1, tandem duplicate 2 ( sst1.2 ) expression increased with the treatment of T and E2 ( P < 0.05), while growth hormone‐releasing hormone ( ghrh ) expression decreased. E2 and T had different effects on growth differentiation factor 8 ( gdf8 ) and insulin-like growth factor-binding protein 7 ( igfbp7 ) expression in the muscle. Expression of gdf8 increased in the treated fishes in contrast to the reduction expression of igfbp7 . This study provided important clues for understanding the role of sex steroids in flatfish SSD.