Steroidogenic Effects of Salinity Change on the Hypothalamus–Pituitary–Gonad (HPG) Axis of Male Chinese Sea Bass (Lateolabrax maculatus)

Abstract

As lower vertebrates, teleost species could be affected by dynamic aquatic environments and may respond to environmental changes through the hypothalamus–pituitary–gonad (HPG) axis to ensure their normal growth and sexual development. Chinese sea bass (Lateolabrax maculatus), euryhaline marine teleosts, have an extraordinary ability to deal with a wide range of salinity changes, whereas the salinity decrease during their sex-maturation season may interfere with the HPG axis and affect their steroid hormone metabolism, resulting in abnormal reproductive functioning. To this end, in this study, 40 HPG axis genes in the L. maculatus genome were systematically characterized and their copy numbers, phylogenies, gene structures, and expression patterns were investigated, revealing the conservation of the HPG axis among teleost lineages. In addition, freshwater acclimation was carried out with maturing male L. maculatus, and their serum cortisol and 11-ketotestosterone (11-KT) levels were both increased significantly after the salinity change, while their testes were found to be partially degraded. After salinity reduction, the expression of genes involved in cortisol and 11-KT synthesis (cyp17a, hsd3b1, cyp21a, cyp11c, hsd11b2, and hsd17b3) showed generally upregulated expression in the head kidneys and testes, respectively. Moreover, cyp11c and hsd11b2 were involved in the synthesis and metabolism of both cortisol and 11-KT, and after salinity change their putative interaction may contribute to steroid hormone homeostasis. Our results proved the effects of salinity change on the HPG axis and steroidogenic pathway in L. maculatus and revealed the gene interactions involved in the regulation of steroid hormone levels. The coordinated interaction of steroidogenic genes provides comprehensive insights into steroidogenic pathway regulation, as well as sexual development, in teleost species.

The Influence of Triphenyltin Exposure on the Osmoregulatory Capacity of Marine Medaka (Oryzias melastigma) at Different Salinities

“…However, alterations in salinity levels can disrupt osmotic pressure regulation, leading to unfavorable impacts on organ functionality. For example, acute salt stress induces a significant decrease in hepatic glycogen content in Mozambique tilapia [14], while declining salinity during the spawning season of Chinese perch may Water 2024, 16, 921 2 of 11 impede steroid hormone metabolism, ultimately resulting in reproductive dysfunction [15]. In the osmoregulation of fish, ion channel proteins such as Na + -K + -ATPase (NKA) and Ca 2+ ATPase play vital roles by regulating dynamic changes in various ion concentrations to adjust to varying salinity environments, thereby, maintaining the homeostasis of the fish, including improving intestinal water absorption [16,17] and plasma ion concentrations [18].…”