In a rare case of fertilisation, a shark was born in an aquarium without the presence of a male specimen, causing a stir in the scientific community as they investigate the unusual occurrence.

The egg was discovered at the Shreveport Aquarium in Louisiana, United States, and the shark Yoko was reportedly born on January 3. 

Yoko, a swell shark (Cephaloscyllium ventriosum) was born in a tank inhabited solely by two adult females. 

The team confirmed that the two female sharks in the tank had not interacted with a male for over three years. 

This suggests that either parthenogenesis, a rare form of asexual reproduction, or delayed fertilisation, where fertilisation happens long after mating, may have taken place. 

To determine the exact cause, the husbandry team plans to karyotype the pup once it reaches an appropriate size for a blood draw, likely in a few months. 

This DNA analysis will provide definitive confirmation of whether the hatchling resulted from parthenogenesis or delayed fertilisation.

Greg Barrick, curator of live animals at the Shreveport Aquarium, said: “This situation is incredible and demonstrates the resilience of this species.”

Yoko, whose name comes from the Chumash word ‘onyok’ for sharks, is being closely monitored.

Yoko’s case began eight months ago when the aquarium caretakers discovered an egg in the swell sharks’ tank. Although it initially went unnoticed, the development was monitored until the shark was born at the beginning of this year. 

This species, native to the coastal waters of the Eastern Pacific Ocean, is known for its ability to inflate its body as a defence mechanism.

Although Yoko is in good health right now, the aquarium acknowledges the inherent risks to pups born under unusual circumstances like this.