In vitro assessment of Na+, Mg2+, Ca2+, and K+ on vitellogenesis and expression of genes related to ovarian development in female Chinese mitten crab, Eriocheir sinensis

Seawater contains a variety of mineral ions, such as Na+, Mg2+, Ca2+, and K+. Although previous studies have shown that brackish water can promote ovarian development of the Chinese mitten crab (Eriocheir sinensis), it remains unclear whether these ions directly affect the ovarian development and vitellogenesis of E. sinensis. Therefore, this study was designed, using in vitro tissue incubation mediums with different concentrations of Na+ (280, 320, 360, and 400 mmol/L), Mg2+ (5, 10, and 15 mmol/L), Ca2+ (5, 10, 15, and 20 mmol/L), and K+ (5.5, 9, and 13 mmol/L), to investigate their effects on Vg/Vn contents and the expression of ovarian development-related genes in the hepatopancreas and ovaries of E. sinensis. The results showed that: (1) Different Na+ concentrations had no significant impact on vitellogenesis and the expression of ovarian development-related genes in both tissues, except for an enhancement of the esEcR2-mRNA levels in the hepatopancreas. (2) The Mg2+ (15 mmol/L) significantly increased the Vg/Vn content in hepatopancreas and ovary. However, the 10 mmol/L Mg2+ group decreased esVgR-mRNA levels and esEcR2-mRNA levels in the ovary compared to the control group. (3) Ca2+ (10 ∼ 15 mmol/L) significantly promoted Vg/Vn content and esVg-mRNA levels in both tissues, which also upregulated the expression of ovarian development-related genes (esERR, esEcR2, and esRXR). (4) Increasing K+ content significantly decreased the Vg/Vn content in hepatopancreas and ovaries. Furthermore, the K+ significantly reduced esRXR-mRNA levels in the ovaries but significantly increased esERR-mRNA levels in both tissues. In summary, under in vitro conditions, Na+ concentration had no significant effect on the vitellogenesis, while Ca2+ (10 ∼ 15 mmol/L) and Mg2+ (15 mmol/L) significantly promoted the vitellogenesis in the hepatopancreas and ovaries of E. sinensis. Additionally, Ca2+ significantly enhanced the expression of genes related to ovarian development, while K+ had a negative impact on the vitellogenesis.