The stingray in Hendersonville, North Carolina, is pregnant but not by a male stingray. The aquarium and outreach center doesn’t have any male stingrays.
Aquarium staff said the mystery began in September 2023, when the ray named Charlotte began to "swell."
"We documented multiple growths internally and initially thought she had a cancer," staff wrote.
The aquarium vet later identified the growths as eggs, not cancer, much to the bewilderment of aquarium workers. The vet noted there have been a few cases of parthenogenesis – or asexual reproduction without fertilization – in stingrays.
Aquarium staff had another thought: In July, a couple of months before Charlotte showed signs of pregnancy, the aquarium moved two male sharks into the tank.
"We started to notice bite marks on Charlotte, but saw other fish nipping at her, so we moved fish, but the biting continued," they wrote. "Then our light bulb went off – sharks bite to mate – did one of our young males mate with her?"
Researchers said sharks and stingrays are closely related, and cross-breeding has been documented.
Charlotte the stingray’s latest ultrasound shows two or three pups that could be delivered any minute. Their estimated due date was Feb. 9, but they hadn’t been born as of Saturday morning.
The aquarium will have to do a DNA test after they’re born to prove their theory, "unless we have visual cues about a mixed breed."