When Gen-chan arrived at a zoo in Japan in 2017, no one questioned whether the then-five-year-old hippopotamus was a boy.
The person in charge of the Mexican zoo where Gen-chan initially lived said the hippo was male and import documents also indicated that information, according to Osaka Tennoji Zoo.
Seven years later, zoo staff made a surprising discovery: Gen-chan, now 12, was female.
"Gen-chan arrived as a male from Mexico's Africam Safari in 2017 and has been raised as a male until now. But as he ages, he does not exhibit male-specific behaviour and his reproductive organs cannot be visually confirmed," Osaka Tennoji Zoo wrote in a blog post translated from Japanese on April 18. "There was some doubt as to whether it was really a male."
Zookeepers noticed Gen-chan didn't make any courtship calls to female hippos and didn't scatter her feces around to mark territory like other male hippos, according to Tokyo Weekender, an English-language lifestyle magazine in Japan.
But the zoo in Osaka, Japan recently confirmed that an outside institution conducted DNA tests and determined the hippo was female.
"However, based on this result, we recognize the importance of reconfirming the sex of introduced animals, and will take precautions to ensure that this does not happen again," Tennoji Zoo wrote on its blog post last week.
It said it won't be changing Gen-chan's name. The hippo's male moniker was chosen through a public contest, Japanese public broadcaster NHK (Japan Broadcasting Corporation) reported.
"We will continue to strive to provide a comfortable environment for Gen-chan, so we hope that you will continue to come and see Gen-chan," Tennoji Zoo wrote.
Sapporo Maruyama Zoo in Japan also admitted on March 1 to making a similar blunder. It wrongly believed that a 21-month-old lion named Clay was male when it was actually female, Tokyo Weekender reported. The zoo realized its mistake when it noticed the animal didn’t grow a mane and didn't pee the same way as other male lions.
Mistaking the gender of animals isn't rare. Earlier in January, fans were surprised to learn that He Ye, a four-year-old giant panda in Chengdu, China, was actually a girl, English-language state newspaper China Daily reported. He Ye was known as the twin "brother" of his sister He Hua, also known as Hua Hua, until a DNA analysis revealed He Ye was female. The twins are popular in China. He Ye had displayed male characteristics when she was younger, but they became less obvious as she grew older, according to China Daily. Experts said that out of all large mammals, the sex of giant pandas is the most difficult to determine, the Chinese publication reported.
