Matsumoto et al.: Sexual maturation in a captive Rhincodon typus based on observations made over 20 years 
81 
Figure 2 
Relationship between the ratio of the clasper outer length to the pelvic inner length 
(CLO:P2I) and body length, given in centimeters in total length (TL), from October 2005 
through October 2013 for a male whale shark (Rhincodon typus) in captivity at the Okinawa 
Churaumi Aquarium in Japan. 
year (1-BK model) or 27.4 cm/year (2- 
BK model) from 1995 through 2008; 
after that time period, the growth rate 
decreased to 0.6-5.6 cm/year. 
Clasper development and functionality 
Clasper elongation was complete in 
11 months (Fig. 2). Before August 
2011, CLO:P2I was almost constant 
(1.00-1.09). After the claspers began 
to elongate posteriorly beyond the tip 
of the pelvic fin, CLO:P2I increased to 
1.60 by July 2012; then this elonga¬ 
tion ended, and the CLO:P2I remained 
constant. 
The shape of the claspers changed 
as the claspers elongated (Fig. 3). Cau¬ 
liflower-shaped tissues were formed at 
the distal ends of the claspers, and 
cartilage associated with the rhipidion 
(small cartilaginous elements located 
at the distal end of the clasper) was 
observed along clasper grooves. 
The clasper became functional dur¬ 
ing a period of rapid elongation with 
skeletal development of the rhipidion. 
The whale shark began to display a 
new behavior in April 2012. The ani¬ 
mal turned upside down, to an in¬ 
verted position, while crossing both 
claspers simultaneously (Fig. 4, Sup- 
pi. Video) (online only). The tips of both 
claspers were spread along the groove 
Figure 3 
Images with ventral views showing morphological changes in the claspers 
of the male whale shark (Rhincodon typus) in captivity at the Okinawa 
Churaumi Aquarium, Japan, taken in (A) October 2005, (B) August 2011, 
and (C) July 2012, as well as (D) an image of a posterior view taken in 
February 2013 of the same whale shark. 
