On January 3, the Shreveport Aquarium in Louisiana welcomed a swell shark pup into the world under mysterious circumstances: It was born in a tank that housed only two sharks—and both were female. The two swell sharks have been in a female-only habitat at the Shreveport Aquarium for more than three years.

According to the aquarium, the shark egg was first spotted eight months ago. The shark hatched a few weeks ago and the team at the aquarium is working to determine how it was conceived. Once the shark is big enough for a blood draw,

The egg was discovered eight months ago but the Shreveport Aquarium believes it may have gone undetected for an additional two months. The team said the two female sharks present in the tank had not been in contact with a male for more than three years,

Officials with the Shreveport Aquarium recently announced the unusual birth of a swell shark pup in a tank where only two female sharks were present.

The female swell shark pup, nicknamed Yoko, hatched at the Shreveport Aquarium in Louisiana, despite no male sharks being present in the tank.