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Chinese mitten crab (Eriocheir sinensis) belongs to Decapoda, Grapsidae and Eriocheir. It is also known as river crab and hairy crab and is widely distributed in the coastal waters of China and has important economic benefits. Salinity is the key environmental factor affecting the mating and spawning of E. sinensis. Presently, reports on the effects of salinity on crabs focus on osmotic pressure regulation, nutritional and energy metabolism, molting, and sexual precocity. However, the effects of salinity on the related hormones in the hemolymph before and after mating and spawning of E. sinensis have not been reported. Relevant steroid hormones include progesterone, 17α-dihydroxyprogesterone, 20β-dihydroxyprogesterone, and 17α-20β-dihydroxyprogesterone (DHP) and most effectively induce maturation of salmon and trout eggs, which has been confirmed in a variety of fish. Early studies have shown that the ovulation activity of fish is closely related to the level of gonadotropin (GTH) in the blood. The gonadotropin releasing hormone receptor (GnRHR) in E. sinensis indicate that the ovarian maturation and reproductive regulation in crustaceans are regulated by some gonadotropins, such as methylfarnesol and ecdysone. PGE, PGF, and prostacyclin (PGI2) can promote ovulation in a variety of fish and crustaceans. Like vertebrates, steroids are important hormones that affect the ovarian development of shrimp and crab, such as estradiol (E2), testosterone (T), and progesterone. Steroids can impact gonadal development and play a very important role in ovarian development and vitellogenesis. However, these hormones are restricted by a variety of environmental factors, such as temperature, light, salinity, and so on. In order to investigate the effect of salinity on hemolymph related hormones during mating and spawning of E. sinensis, the spawning salinity was set at 0, 2, 4, 6 and mating salinity set at 3, 6, 9, 12, 15, 18, 21. Five samples were collected from specimens in each salinity to analyze the contents of DHP, GTH, PG, E2, and testosterone in the hemolymph of female E. sinensis before and after mating and spawning under different mating and spawning salinities. The components were detected by ELISA at the wavelength of 450 nm using the kit double antibody sandwich method. Results revealed: (1) in fresh water, female crabs displayed no mating behavior. When the salinity was lower than 6, female crabs only mated without spawning. (2) There were no significant changes in PG, E2, or testosterone in the hemolymph of female crabs after mating in low salinity (2–6), and there was no significant difference between crabs at different salinities after mating (P > 0.05). (3) The contents of DHP, PG, E2, and testosterone in the hemolymph of female crabs initially decreased and then increased with salinity before spawning. After spawning, DHP, PG, and E2 in hemolymph initially increased and then decreased with increased salinity. When the salinity was 18, DHP, PG, E2, and testosterone in the hemolymph of the female crab after spawning decreased to the lowest level, and there was a significant difference between the before and after spawning results (P < 0.05). (4) At 6 salinity, the contents of DHP, PG, E2, and testosterone in the hemolymph of female crabs before spawning were the highest and the contents of DHP and PG decreased after spawning, while the contents of E2 and testosterone increased. However, there was only significant variation in the DHP from before spawning to after spawning (P < 0.05), and there was no significant difference in the other indexes (P > 0.05). The content of testosterone in the hemolymph initially decreased and then increased before and after spawning. This comprehensive study showed that salinity effects the five hormones in the hemolymph of female E. sinensis during the reproductive and breeding stage. Among them, the five hormones do not change significantly during the mating process of E. sinensis. DHP, GTH, and PG are involved in the oviposition of E. sinensis. The analyses of the changes in the related hormones in the hemolymph of female E. sinensis before and after mating and spawning at different salinities have identified changes in the neutral hormones. These results provide details on the reproductive regulation mechanism of E. sinensis and provided basic reference data for researching the reproductive biology of E. sinensis. |
