Osaka Zoo Thought Hippo Gen-chan Was a Male for Seven Years…

The Tennoji Zoo in Osaka, Japan has housed a resident hippopotamus named Gen-chan since 2017. Gen-chan, acquired from Mexico, was believed to be a male specimen all this time. However …

Gen-chan arrived as a male from Africam Safari Puebla, Mexico in 2017 and has been raised as a male until now,” the zoo explains on its blog, “but as he ages, he does not exhibit male-specific behavior and his reproductive organs cannot be visually confirmed. There was some doubt as to whether it was really a male.”

Now that the zoo has conducted a DNA test, there is no doubt that Gen-chan is in fact female. We have so many questions, but now we know that hippos do not have obvious external genitalia. Sure, females have a vulva and the males have a penis, but the latter is usually tucked within a sheath, so telling the two apart can be difficult.

The zoo did not specify which male-specific behaviors Gen-chan eschews. We’ll assume that she had never, for example, exhibited ritualized dung-showering, in which the tail swings rapidly back and forth while feces mixed with urine is showered for several feet in all directions. Only boys do that.

When the zoo acquired Gen-chan, who was five years old at the time, the accompanying documents required for import indicated that the big “guy” was a male. It’s crucial info for a zoo to know because hippos socialize according to gender roles: a herd is usually composed of females, with one male in charge of all. 

“We recognize the importance of reconfirming the sex of introduced animals,” the zoo says, “and will take precautions to ensure that this does not happen again.” There are no plans to change Gen-chan’s name.

Photo credit: Tennoji Zoo