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1 October 2015 Gonadal Morphology, Histology, and Endocrinological Characteristics of Immature Female Whale Sharks, Rhincodon typus
Ryo Nozu, Kiyomi Murakumo, Rui Matsumoto, Masaru Nakamura, Keiichi Ueda, Keiichi Sato
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Abstract

Captive breeding of whale sharks is one of the great challenges for aquariums. However, there is limited information available related to reproductive physiology due to the difficulty of sampling and long-term observation. In the present report, we provide information on the reproductive physiology of female whale sharks, which were incidentally captured as bycatch in a set-net off the coast of Okinawa, Japan. Total lengths of three captured female whale sharks were 403, 665, and 761 cm, respectively, at the time of their death. Collected paired ovaries differed in size between right and left. However, it seems not to determine which side of ovary becomes developed. Histological observations revealed that oocytes surrounded by follicle cell layers localized in the developed ovary, and most developed oocytes exhibited yolk vesicle stage. Additionally, in the largest specimen, there were low levels of three steroid hormones (Testosterone, Dihydrotestosterone, and Estradiol-17ß) that did not show seasonal variation. The present results indicate that even the whale shark over 7 m in TL are still histologically and endocrinologically immature. We expect that the present data will provide fundamental information related to reproductive physiology of female whale sharks, and will contribute to protection activities and increased success in captive breeding of whale sharks.

© 2015 Zoological Society of Japan
Ryo Nozu, Kiyomi Murakumo, Rui Matsumoto, Masaru Nakamura, Keiichi Ueda, and Keiichi Sato "Gonadal Morphology, Histology, and Endocrinological Characteristics of Immature Female Whale Sharks, Rhincodon typus," Zoological Science 32(5), 455-458, (1 October 2015). https://doi.org/10.2108/zs150040
Received: 30 March 2015; Accepted: 1 May 2015; Published: 1 October 2015
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KEYWORDS
female
Histology
immature
ovary
sex steroid hormones
Whale shark
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