Abstract
Eels do not mature under captive conditions. It is not uncommon for fish to begin and complete their final maturation under closed aquaculture conditions. In most cases, they proceed and successfully complete vitellogenesis and spermatogenesis. However, oocyte maturation and ovulation, and sperm maturation is not spontaneously triggered under aquaculture conditions, which is different from their natural spawning places. The difficulty of eel reproduction is that female and male eels will not proceed vitellogenesis and spermatogenesis, respectively. The Japanese eel undergoes vitellogenesis and spermatogenesis during long-distance migration toward the spawning site. Thus, because natural eels have not been captured during spawning migration in the ocean, the natural controls that promotes sexual maturation and final maturation are not known. Previous studies have provided the current known information on natural reproductive conditions by examining adult eels captured at their spawning ground, West Mariana Ridge; however all these eels had already completed ovulation or spawning (Tsukamoto et al. 2011; Shimizu et al. 2021). Therefore, reproductive physiological conditions can only be determined from artificially induced sexually maturing eels. In a previously published study, we described the control of ovarian vitellogenic growth with special focus on changes in the morphology of oocytes and steroid hormone production in the ovary of the Japanese eel (Adachi et al. 2003). In this chapter, we describe the latest insights, especially into natural sex differentiation and the mechanism of steroidogenic shift that promotes final oocyte maturation in the Japanese eel.
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13 February 2024
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Ijiri, S., Matsubara, H., Horiuchi, M., Kazeto, Y. (2023). Reproduction. In: Tsukamoto, K., Kuroki, M., Watanabe, S. (eds) Eel Science. Fisheries Science Series. Springer, Singapore. https://doi.org/10.1007/978-981-99-5692-0_12
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DOI: https://doi.org/10.1007/978-981-99-5692-0_12
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