Who’s the daddy? Baby shark hatched at aquarium with no males might not have one

A surprising discovery was made at a Louisiana aquarium when an egg appeared in a shark tank with only two female residents. The two female sharks, Ethel and Lucy, had not had contact with any males for over a decade, leaving staff puzzled as to how the egg got there.

After the egg hatched on January 3, 2025, the pup was named Yoko by Greg Barrick, the curator of live exhibits at the Shreveport Aquarium. Yoko, short for Onyoko, which means shark in the Chumash language, is doing well and staff are currently determining the pup’s sex.

The aquarium is still unsure which of the two adult females is Yoko’s mother and has no idea who the pup’s father is, or if there even is one. The mystery surrounding Yoko’s parentage could be explained by either parthenogenesis, where a female reproduces asexually, or delayed fertilization, where sperm is stored until the conditions are right for reproduction.

Shark scientist Bob Hueter explains that parthenogenesis is not as uncommon as one might think and has been observed in about a dozen species of sharks. This phenomenon allows females to self-fertilize their own eggs when they do not encounter a male mate. Delayed fertilization, on the other hand, involves a female storing sperm from a previous mating until she is ready to reproduce.

Genetic testing will be conducted to determine if Yoko is a genetic copy of either Ethel or Lucy, indicating parthenogenesis, or if there was a father involved through delayed fertilization. Barrick believes that the latter is unlikely, as the two female sharks have been in male-free environments since at least 2014.

While parthenogenesis may have downsides in terms of genetic diversity in the wild, a single generation of parthenogenesis in an aquarium setting is likely not a cause for concern. However, Barrick notes that there have been instances of health problems in parthenogenesis offspring due to recessive traits.

Staff at the Shreveport Aquarium are closely monitoring Yoko to ensure her well-being. Despite the mystery surrounding her parentage, Yoko appears to be healthy and thriving in her new environment. The unexpected arrival of this baby shark without a known father has certainly captivated the attention of aquarium staff and visitors alike.