A female whitespotted bamboo shark has given birth to three baby sharks without having been near a male shark in six years.

The Detroit Free Press reported Friday that scientists at Detroit's Belle Isle Aquarium are puzzled how she did this.

"Fish do so many quirky things," said Doug Sweet, curator of fish at the aquarium. "Even though this is exciting for us, we're, like, 'Well, those darn fish are doing it again.' We kind of expect half-crazy things from them."

For the time being scientists are calling it a "virgin birth."

It happens.

The female bamboo shark, about 60 centimetres long, laid her eggs in late winter. Sweet left them in the tank she inhabited, having heard of a bonnethead shark at a Nebraska zoo that had a virgin birth in 2001.

The first blessed event happen in July. The third egg hatched in September. Sweet expects more baby sharks will be born in the next several weeks.

Possible explanations:

  • [A] The female was impregnated before she arrived at the Detroit aquarium by having a male's sperm in her reproductive tract. (Sweet says this is highly unlikely as females this size don't breed.)
  • [B] The female could have both male and female reproductive characteristics and be able to self-fertilize. (Sweet says this would be even more unusual than [A].)
  • [C] The female shark somehow stimulated the eggs without sperm, a process known as parthenogenesis. (Sweet said this is extremely rare.)

The next step to solve the puzzle is to resort to genetic testing of the female sharks and her babies.