Abstract
To improve understanding of the mechanism of early ovarian development in eels, the effects of water temperature decrease on oocyte development, plasma levels of sex steroids [estradiol 17β (E2), testosterone (T), 11-ketotestosterone (11-KT)], and gonadotropin β-subunit [follicle-stimulating hormone (FSHβ), luteinizing hormone (LHβ)] messenger RNA (mRNA) expression levels were investigated. A total of 27 female Japanese eels Anguilla japonica were divided into initial, control, and test (water temperature decrease) groups. Starting on 22 September 2009, eels in the test group were reared in a tank with gradual temperature decrease from 25°C to 15°C over 39 days, while the control group was maintained at 25°C. The test group accumulated more oil droplets in their oocytes than did the other groups. Levels of sex steroids, especially 11-KT, were higher in the test group. In contrast, FSHβ and LHβ mRNA expression levels were lower in the test group. These results suggest that water temperature decrease only induced an early stage of ovarian development that was partly affected by an 11-KT increase. For further maturation, other environmental factors related to induction of gonadotropin increase appear to be needed.
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Acknowledgments
We are grateful for K. Kikuchi, N. Mizuno, Y. Jo, and the other members of Fisheries Laboratory, Graduate School of Agricultural and Life Sciences, the University of Tokyo for assistance in coordination for data collection in the laboratory. We also thank M.J. Miller for helping improve the manuscript. We are grateful to M. Oya for assistance and encouragement with many aspects of the study. The first author (R.S.) was supported by a Research Fellowship of the Japan Society for the Promotion of Science for Young Scientists (No. 20-4652).
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Sudo, R., Tosaka, R., Ijiri, S. et al. Effect of temperature decrease on oocyte development, sex steroids, and gonadotropin β-subunit mRNA expression levels in female Japanese eel Anguilla japonica . Fish Sci 77, 575–582 (2011). https://doi.org/10.1007/s12562-011-0358-3
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DOI: https://doi.org/10.1007/s12562-011-0358-3