Through long term rearing of the whale shark “Jinta” at Okinawa Churaumi Aquarium, we have been able to discover the morphological and physiological changes that occur as a male whale shark reaches sexual maturation. This is a world’s first.

• The whale reached 8.5 meters in length and its claspers (genitals) rapidly elongated over 11 months.
• Concentrations of sex hormones (testosterone and progesterone) increased as the claspers elongated.
• Additional behaviors including movements of the claspers, and the discharge of semen have also been observed as Jinta sexually matured.
• It is estimated from previous studies and by the speed of his growth, that Jinta reached sexual maturity at around 25 years old.

We hope to contribute to conservation and an understanding of whale shark ecology through our studies of reproduction and long-term rearing of the whale shark.

Authors

Rui Matsumoto, Yosuke Matsumoto, Keiichi Ueda, Miwa Suzuki, Kiyoshi Asahina, Keiichi Sato (Bold Letters: Staff members of Churashima Foundation)

Title of Paper

Sexual maturation in a male whale shark (Rhincodon typus) based on observations made over 20 years of captivity.

Title of Journal

Fishery Bulletin

Article link

https://spo.nmfs.noaa.gov/sites/default/files/pdf-content/fish-bull/matsumoto_1.pdf

A distinctive reproductive behavior of a male (turns its body upside down as it crosses its claspers)

Changes in concentration of sex hormone (testosterone) and clasper elongation.