A world’s first! Confirmation of male whale shark’s sexual maturation

Okinawa Churaumi Aquarium managed by the Okinawa Churashima Foundation has been studying the male whale shark named Jinta that has lived in the large Kuroshio Sea tank for over 20 years. They have described in an academic journal the whale shark’s growth and the process of its sexual maturation.

≪About Whale Sharks≫
Scientific name：：Rhincodon typus

They are widely distributed from temperate to tropical waters. Whale sharks are the world’s largest fish and can grow to more than 13 meters in length. Jinta, the male whale shark living in Okinawa Churaumi Aquarium, has been reared since March 1995. At 24 years, this is the world’s longest rearing record for a whale shark.

Much of the ecology of whale sharks is not clear, there is limited information especially on reproduction and sexual maturation. Okinawa Churaumi Aquarium, has been able to document in detail the physical and behavioral changes in Jinta as he grew and reached sexual maturity.
The results have been published in the international academic journal Fishery Bulletin.
The following points were revealed by the research.

1. When the individual was 8.5m in total length, the claspers began to get longer, (growth lasted around 11 months)
2. Sex hormones (testosterone and progesterone) increased as the claspers grew longer.
3. After growth, new behaviors were displayed including the movement of claspers, and semen was discharged through the clasper grooves, indicating that after clasper growth the male was functionally mature.
4. Observations from previous findings suggest that Jinta reached maturity when he was over 25 years in age.

The research of physiological changes could only have been observed through captive rearing and monitoring the same individual. At Okinawa Churaumi Aquarium, we hope to contribute and shed light on the ecology and conservation of whale sharks and to promote studies in reproductive research through continued rearing of the whale shark.

Underwater blood test
Behavior since sexual maturation

Detailed information is published in the international academic journal:

Title of Journal： Fishery Bulletin. DOI: 10.7755/FB.117.1-2.9

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

Authors：Rui Matsumoto, Yousuke Matsumoto, Keiichi Ueda, Miwa Suzuki, Kiyoshi Asahina, Keiichi Sato

More information is given on the monitor displayed on the side of the main tank of the Kuroshio Sea tank at the whale shark and manta ray corner within the Okinawa Churaumi Aquarium.