A miraculous birth: a female shark, having not seen a male for three years, unexpectedly gave birth to a pup.

The Shreveport Aquarium in Louisiana kicked off 2025 with astonishing news: a female California swell shark (Cephaloscyllium ventriosum) unexpectedly gave birth to a pup in early January unexpectedly appearing. The most intriguing aspect of this story is that the female shark had not interacted with a male for over three years, reports Popular Science.

Researchers are unsure exactly how the pup came to be, but they suspect there are several possible explanations:

• delayed fertilization;
• an unusual reproductive phenomenon — parthenogenesis.

It’s important to note that parthenogenesis is a reproductive strategy in which primarily female gametes can develop without fertilization. This process is typically observed in plants and some invertebrates, including aphids, ants, wasps, and bees. However, scientists have also documented this behavior in some higher vertebrates, such as sharks, snakes, and certain birds. Experts believe that sharks may resort to parthenogenesis as a last resort if they cannot find a mate.

Aquarium staff noted that the shark's egg was first spotted eight months ago, and the pup was born on January 3. Now, experts are focused on studying how exactly it was conceived. Once the shark is large enough for a blood sample, scientists will conduct a DNA analysis that will provide answers to this question. The mystery is expected to be unraveled in the coming months. If it is not parthenogenesis, the pup may have been born as a result of delayed fertilization, which occurs in sharks when a female retains some sperm from previous encounters to use for future eggs.

According to Greg Barrick, curator of live animals at the Shreveport Aquarium, this situation is quite extraordinary and demonstrates the resilience of the species. Experts also hope that the mystery of the pup's origin will be resolved in the next few months.

In the wild, California swell sharks inhabit the coastal waters of the eastern Pacific Ocean. They feature spots along their scales and can grow up to three feet in length, and are best known for their ability to inflate their bodies with water and air. This strategy helps them deter predators.

Experts report that the pup has been nicknamed Yoko. Currently, the shark is doing well, but it is known that young sharks born through parthenogenesis face significant challenges. For instance, previous studies have shown that offspring born from parthenogenesis often die young. However, scientists still do not know why this occurs but suspect that the manifestation of a lethal recessive gene may lead to the premature death of the pups.