A swell shark egg has hatched in the USA – even though no male shark had been present in its aquarium habitat to fertilise it for at least three years.
The egg was first identified by the husbandry team at Shreveport Aquarium in Louisiana in the spring of 2024, though it could have lain undetected in the tank since as long ago as February.
Swell shark egg-cases normally take nine months to a year to hatch, and the team knew that the two female sharks occupying the habitat had not been in contact with a male shark since before the Covid pandemic in early 2021.
Swell sharks (Cephaloscyllium ventriosum) are a type of cat shark native to eastern Pacific coastal waters. Their name derives from a unusual ability among sharks to inflate their bodies with air or water to intimidate predators.
The egg was closely monitored in the aquarium’s quarantine facility until the pup hatched on 3 January, assisted by the team.
The birth appears to be either a rare case of asexual reproduction, known as parthenogenesis, or of fertilisation delayed for an extended period after mating.
After a few months the husbandry team will be able to sample the pup’s blood for the purposes of DNA analysis to find out which of these unusual circumstances applies.
“This situation is incredible and shows the resilience of this species,” said the aquarium’s curator of live animals Greg Barrick. “We are very excited in the coming months to confirm whether this was indeed a case of parthenogenesis or if it was delayed fertilisation. It really proves that life… finds a way.”
Not on display
The baby swell shark, named Yoko from onyoko, a Chumash (Native American) word for shark, was said to be thriving. However, sharks born through rare reproductive events are known to face significant health challenges, so Yoko is not yet on display and continues to be closely monitored.
Asked when the danger to life would recede, Barrick told Divernet: “I'm not sure we can ever really relax on that front but we definitely will be more confident after maybe her first birthday.”
Last year, a sting ray called Charlotte was found to be pregnant in a North Carolina aquarium despite not having been in contact with a male ray for eight years. This was suspected to be either a case of parthenogenesis or impregnation by a shark.
Social-media followers who had initially celebrated the pregnancy grew impatient and abusive towards aquarium staff when the ray failed to deliver the expected pups. She later died after being found not to have been pregnant but to have a reproductive disease.
Parthenogenesis was first documented in Komodo dragons in British zoos in 2006, and has been recorded occasionally in zebra sharks and sawfish but remains rare in vertebrates. Why it occurs and its triggers remains unknown.
Also on Divernet: ‘Peculiar’ white shark likely first live newborn ever seen, Rare access: Hammerhead shark embryos, Baby sharks face uncertain future, Rare shark nursery found in Atlantic
