The world's largest living coral reef aquarium is wondering how an upside-down jellyfish brought forth 200 babies in her own tank.

Townsville, Queensland's Reef HQ placed a lone jellyfish alone in a tank. The aquarium staff was surprised to see that the lone jellyfish is now surrounded by over 200 jellyfish babies.

How did it happen? The Sunday Mail calls it 'immaculate conception.' Reef HQ is still conducting an investigation.

The jellyfish was placed in a tank that had previously contained an injured jellyfish, which died four months earlier.

One of the theories being discussed is that the polyps, which have now grown into healthy baby jellyfish, may be clones of their parent.

"Jellyfish clone very easily. When some jellyfish are cut in half, you get two jellyfish," said Reef HQ aquarist Krystal Huff. "Since the parent jellyfish was injured, it had damaged tissue cells which could have grown into other jellyfish... But we don't know if the parent reproduced with another jellyfish without us noticing."

These jellyfish are often found in shallow water in mud and sandflats around the Great Barrier Reef.

In other developments, Reef HQ has recently housed the birth of baby seahorses, and will see the hatching of leopard eggs in a few months.