Earlier this year, there was a bit of a mystery at the Aquarium and Shark Lab in Hendersonville, North Carolina, after a stingray appeared to become pregnant despite no male stingrays being present. While an interesting mystery in its own right, the case drew extra attention after suggestions by the head of the aquarium that the stingray could have been impregnated by a shark. After a series of tests, however, the team has found “truly a sad and unexpected medical development.”
“Our stingray, Charlotte, is expecting! We have held this close to our hearts for over 3 months,” Team ECCO, which runs the aquarium, announced on Facebook in February, alongside ultrasound scans. “The really amazing thing [i]s we have no male ray!”
There are of course a few options for how a ray could become pregnant without the presence of a male. Some species of ray can store sperm for later use, but no male stingrays have been kept in the tank with Charlotte at all, Brenda Ramer, founder and executive director of Team ECCO, told ABC 13 News at the time.
However, there were males of another species in there with her, leading to the unlikely claim that a shark could have impregnated her.
“In mid-July 2023, we moved two 1-year-old white spot bamboo males (sharks) into that tank. There was nothing we could find definitively about their maturation rate, so we did not think there would be an issue,” said Ramer. “We started to notice bite marks on Charlotte, but saw other fish nipping at her, so we moved fish, but the biting continued.”
During mating, male sharks – including bamboo sharks – bite the females in order to get into position, suggesting to the team that this might be an explanation. Hybrids are possible, though generally between two genetically similar species that have not long diverged, and there are no documented cases of sharks breeding with stingrays.
Hybrids of species that parted ways long ago have been discovered, but they are incredibly rare. In 2020, a team found a hybrid of an American paddlefish and a Russian sturgeon, two species that last shared an ancestor in the Jurassic era.
Ultimately, this idea was always very unlikely.
“I’m going to stop this misinfo in its tracks,” Dr Noah Bressman, assistant professor of physiology at Salisbury University, explained on Bluesky. “Sharks [and] rays are as distantly related as humans [and] snakes, so a snake knocking up a human is just as likely as a shark knocking up a ray.”
Another idea was proposed, though this too would be revealed as incorrect. Rays can reproduce sexually, but in rarer cases, they can develop an embryo without fertilization. This is known as parthenogenesis, a term that stems from the Greek words for “virgin birth”. Birth by this method, though still uncommon, happens every now and then. In fact, one shark at the aquarium has given birth via parthenogenesis 14 times.
Though it is rarer in rays, it was still more likely than a hybrid. However, after a series of tests, the team has found a grimmer explanation; the stingray was unwell.
“We regret the delay of updates regarding Charlotte. This time was necessary to gather data and analyze lab and testing results,” the aquarium wrote on Facebook on May 30. “The reports show that Charlotte has developed a rare reproductive disease that has negatively impacted her reproductive system. The findings are truly a sad and unexpected medical development.”
“Our priority is to focus on Charlotte’s health and wellbeing. We will work with, and be guided by, veterinarians and specialists to better understand this disease and the treatment options for Charlotte,” the team added, though there was no comment on whether the stingray remained, or was ever, pregnant.
“While the research of this disease is limited, we hope that Charlotte’s case and medical treatment will positively contribute to science and be of benefit to other rays in the future.”
