The Shreveport Aquarium in Louisiana kicked off 2025 with a mysterious birth. A swell shark (Cephaloscyllium ventriosum) pup hatched at the facility on January 3, yet the two female sharks present in the tank have not been in contact with a male in over three years. The team at the aquarium suspects the birth could be delayed fertilization or a rare reproductive phenomenon called parthenogenesis.
Parthenogenesis is a reproductive strategy where primarily female sex cells called gametes can develop without fertilization. It is commonly seen in plants and some invertebrate animals (including aphids, ants, wasps, and bees). However, some higher vertebrates–like sharks, snakes, and some birds–may reproduce this way from time to time. In sharks, it is usually reserved as a last resort if there aren’t any mates to go around.
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, DNA analysis should provide answers in the next few months. If not parthenogenesis, it could have been born via delayed fertilization. In sharks, this is when a female will store some sperm cells from previous encounters to use on future eggs.
“This situation is incredible and shows the resilience of this species,” Greg Barrick, the Curator of Live Animals at Shreveport Aquarium, said 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.”
In the wild, swell sharks are found in coastal waters of the eastern Pacific Ocean. They have spots along their scales and can grow up to three feet long. Swell sharks are best known for their ability to swell their bodies with water or air as a way to deter predators. The new swell shark is nicknamed Yoko after the Chumash word for shark (onyok).
Yoko is currently doing well, but young sharks born during rare reproductive events do face some significant challenges. Offspring born from parthenogenesis often die young, yet scientists are still not sure why. They suspect the expression of a lethal recessive gene could kill the pups prematurely.
[ Related: A virgin birth in Shedd Aquarium’s shark tank is baffling biologists. ]
“Should Yoko’s time with us be brief, it will still leave an unforgettable legacy, contributing invaluable insights to the study of shark reproduction and conservation efforts,” the aquarium wrote.
Yoko is currently being closely monitored away from public view for its health and well-being.
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