Nature is capable of some pretty incredible phenomena and even a few mysteries. That’s become all the more apparent recently at Shreveport Aquarium in Louisiana, where the team is celebrating the hatching of an egg that seems to have only one parent.

Last year, a swell shark egg was discovered by the aquarium’s husbandry team and since then, they’ve kept a careful watch on it. Eight months later on January 3, 2025, the swell shark pup was successfully hatched. 

Swell sharks are so named because they can inflate their bodies with seawater as a predator defense mechanism. They are found along the stretch of coast from California to Mexico, as well as Chile, and lay eggs that can hatch in nine to 12 months depending on the temperature of the water.

While baby sharks might seem part and parcel of life at an aquarium, this particular egg-hatching is something of a mystery. The aquarium has two adult female swell sharks, but no males, and the team has also confirmed that neither female has been in contact with a male for over three years. So how can one of them have been able to lay an egg?

Well, swell sharks are part of a group of animals that are capable of two biological processes that might have allowed this to occur. The first is delayed fertilization: female swell sharks can store sperm from males within their bodies and fertilization of the egg can occur a long time after mating. 

The second option is a process called parthenogenesis, which is a form of asexual reproduction that does not involve a male. Instead of requiring sperm, the female is able to use entirely her own genetic material to reproduce.

Parthenogenesis has been found in over 80 vertebrate taxa, and is common in species such as lizards or fish, but much rarer in species like sharks. In 2024, Charlotte the stingray created a global stir as people wondered if her apparent pregnancy was the result of parthenogenesis or the creation of the first “shringray”, a shark-ray hybrid – she hadn’t lived with male stingrays for at least eight years, but did live in a tank with male sharks. However, Charlotte was later found to have gynecological disease and eventually passed away. 

For the swell shark pup, now named Yoko – after the Chumash word for shark, “’onyoko” – the team plans to take a blood sample once it has grown big enough. The DNA in the blood will allow the team to find out if Yoko is the result of delayed fertilization or parthenogenesis.

“This situation is incredible and shows the resilience of this species,” said Greg Barrick, the Curator of Live Animals at Shreveport Aquarium in a statement. “We are very excited in the coming months to confirm whether this was indeed a case of parthenogenesis or if it was delayed fertilization. It really proves that life… uh… finds a way.”