When Japan's Osaka Tennoji Zoo took in a hippo named Gen-chan seven years ago, they were told the young animal was a male. Recently, they took a DNA test and found out the mammal is actually a female. 

In a post on their website, the zoo said that Gen-chan came to the zoo from Mexico's Africa Safari in 2017. When they took the hippo in, Mexico zoo officials and transfer documents all indicated it was a male, the Tennoji Zoo said.

"The animal was only 5 years old at the time and was still a child," a translation of the Japan zoo's post on the discovery says. "We had no doubts." 

That was until zookeepers at Osaka Tennoji noticed Gen-chan was not displaying behaviors typically associated with male hippos. One of the most typical behaviors of male hippos, for example, is whipping their tails in a propeller-like motion while defecating to mark their territory, which Gen-chan did not do, zookeepers told AFP. The hippo also failed to make courtship calls to females and caretakers were never able to identify any male genitalia. 

That's when they decided to order a DNA test to find out what was going on – and discovered that Gen-chan is actually a female. And while her sex will be switched on documents, the 12-year-old hippo's name will not be changing, officials said. 

"We recognize the importance of reconfirming the sex of introduced animals and will take precautions to ensure that this does not happen again," a translation of the post says. "We will continue to strive to provide a comfortable environment for Gen-chan."