Baby shark mysteriously born in aquarium tank housing only females

Yoko the baby swell shark was born in Louisiana's Shreveport Aquarium in early January. Morgan Nix via CNN Newsource

The arrival of a baby swell shark at an aquarium in Louisiana has caused a wave of excitement, after the egg hatched despite the fact that no male sharks appear to have been involved.

Shark pup Yoko was born in early January, Shreveport Aquarium said, having hatched from an egg in a tank containing two female sharks but no male ones.

In fact, neither of the sharks that could have laid the egg had had any contact with a male for more than three years, the aquarium said.

Despite the lack of male sharks in the enclosure, there are two possible ways that the egg could have produced a baby, it suggested.

A phenomenon called parthenogenesis, a form of asexual reproduction where the embryo develops from an egg without fertilization, could have occurred, the aquarium said.

Alternatively, delayed fertilization – where fertilization occurs long after mating happens – could have taken place, it suggested.

Kevin Feldheim, manager of the Pritzker Laboratory for Molecular Systematics and Evolution, whose research focuses on the mating system and population biology of sharks, told CNN that parthenogenesis has been witnessed in a number of shark species, including the zebra shark and whitespotted bamboo shark. It is also thought to have occurred in one species of ray.

Parthenogenesis usually happens when females are isolated from males, Feldheim said, though there are examples of females giving birth this way even when males have been present.

“How parthenogenesis kicks in or what cues the females… to begin the process remains to be discovered,” Feldheim pointed out, adding that “in general, we think that this is a last ditch effort by the female to pass on her genes.”

“It speaks to how adaptable sharks are in terms of their reproduction,” he said.

Feldheim also said scientists currently know “next to nothing regarding how long females can store sperm in each species.” In one shark species, a female was found to have stored sperm for at least 45 months, he said.

Shreveport Aquarium said that it will undertake genetic testing on Yoko when the pup is old enough, to determine exactly how it came to be.

“This situation is incredible and shows the resilience of this species,” Greg Barrick, the aquarium’s curator of live animals, said in a press release.

“We are very excited in the coming months to confirm whether this was indeed a case of parthenogenesis or if it was delayed fertilization. It really proves that life… finds a way.”