78 
National Marine 
Fisheries Service 
NOAA 
Abstract —A male whale shark 
(Rhincodon typus) has been kept in 
captivity at the Okinawa Churaumi 
Aquarium, Japan, for 23 years, pro¬ 
viding a rare opportunity to observe 
sexual maturation of a male. In 
2012, when the individual was 8.5 
m in total length (TL), the claspers 
began to elongate, and the distal 
ends of the claspers changed into 
cauliflower-shaped forms. These 
morphological changes in the clasp¬ 
ers were completed in 11 months. 
Plasma concentrations of sex hor¬ 
mones (testosterone and progester¬ 
one) increased in association with 
clasper elongation. After elongation, 
additional movements, including 
the adduction and crossing of clasp¬ 
ers, were displayed, and a whitish 
fluid, which may have been semen, 
was discharged through the clasper 
grooves, indicating that the male 
was functionally mature after clasp¬ 
er elongation. These observations in¬ 
dicate that this captive whale shark 
reached maturity when it was 8.5 m 
TL and over 25 years in age. This 
size at maturity is consistent with 
observations in the wild. However, 
maturity in this individual captive 
animal may have occurred later 
than has been previously reported 
in nature. 
Manuscript submitted 7 September 2018. 
Manuscript accepted 11 April 2019. 
Fish. Bull. 117:78-86 (2019). 
Online publication date: 26 April 2019. 
doi: 10.7755/FB.117.1-2.9 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Fishery Bulletin 
established in 1881 -cr. 
Spencer F. Baird 
First U S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Sexual maturation in a male whale shark 
(r Rhincodon typus ) based on observations 
made over 20 years of captivity 
Rui Matsumoto (contact author ) 12 
Yosuke Matsumoto 1 
Keiichi Ueda 1 - 2 
Miwa Suzuki 3 
Kiyoshi Asahina 3 
Keiichi Sato 1 - 2 
Email address for contact author: r-matsumoto@okichura.jp 
1 Okinawa Churaumi Aquarium 
Ishikawa 424 
Motobu, Okinawa 905-0206, Japan 
2 Okinawa Churashima Research Center 
Ishikawa 424 
Motobu, Okinawa 905-0206, Japan 
3 College of Bioresource Sciences 
Nihon University 
Kameino 1866 
Fujisawa, Kanagawa 252-0880, Japan 
In the wild, tracking animals, espe¬ 
cially migratory aquatic vertebrates, 
throughout their entire life histories 
is extremely difficult. Animals often 
move over vast oceans and have long 
life spans, sometimes longer than 
those of humans. Therefore, the life 
history traits of such animals gener¬ 
ally are based on fragmented infor¬ 
mation, obtained from dead speci¬ 
mens acquired opportunistically. 
The process of sexual maturation 
in the whale shark (Rhincodon ty¬ 
pus), the world’s largest fish, remains 
poorly understood because of the dif¬ 
ficulties associated with following in¬ 
dividuals over long periods of time, 
both in the wild and in captivity. The 
Okinawa Churaumi Aquarium, locat¬ 
ed in Okinawa, Japan, has success¬ 
fully maintained a whale shark for 
over 20 years in captivity, providing 
a unique opportunity to better fol¬ 
low maturation history in this spe¬ 
cies (e.g., Uchida et al., 2000; Mar¬ 
tin, 2007). This male whale shark, 
named Jinta, has been exhibited 
since 1995 at the Ocean Expo Aquar¬ 
ium (renamed the Okinawa Churau¬ 
mi Aquarium in 2002), representing 
the longest period of captivity for 
this species in the world. From 1995 
to 2018, the total length (TL) of the 
animal increased from 4.6 to 8.7 m. 
From our study of this shark, we 
report the process of sexual matura¬ 
tion in the male whale shark, focus¬ 
ing on morphological changes and 
movements of the claspers, possible 
semen ejection, and changes in the 
circulating levels of sex hormones. 
For male elasmobranchs, the degree 
of clasper elongation and calcifica¬ 
tion and increase in sex hormone 
levels are generally used as indica¬ 
tors of sexual maturation (Gelsleich- 
ter and Evans, 2012); however, con¬ 
tinuous changes in these indicators 
