A double-headed prawn almost ended up as lunch for some sharks at a north Queensland aquarium before being discovered by staff.

Aquarist Laura Colton, from Reef HQ Aquarium in Townsville, said she was preparing to feed the aquarium's baby leopard sharks when she came across the prawn.

"I was counting out a few prawns and fish and I grabbed a handful prawns, and at first I thought there were two stuck together and then realised it was a prawn with two heads," Ms Colton said.

"I have never seen anything like this and neither has anyone else in the team."

She said she had to double check the crustacean to make sure it was not just two prawns stuck together.

"The next thing I looked for was to see if it had been caught in the middle of a moult, so they do shed that skeleton on the outside," Ms Colton said.

"It wasn't that either so if you had a look at the animal, there's two guts in there, even two sets of legs coming from the front part as well, so it's definitely two heads."

Reef HQ has posted the photo of the prawn on its Facebook account, attracting hundreds of comments and shares.

Radiation unlikely to have caused deformity

James Cook University Professor Dean Jerry, the director of Australian Research Council hub for advanced prawn breeding, said the odds of seeing a two-head prawn was in the hundreds of millions.

"A double-headed prawn is extremely rare," he said.

"I've been talking to a couple of farmers today who every year roll out millions of prawns and they've never seen one.

"It's like seeing a two-headed cow or something like that, it may occur quite regularly during early development but these animals are very unfit and they would die eventually."

Professor Jerry wants to carry out genetic testing on the prawn to determine why it has two heads.

"I would take an educated guess that it was like a Siamese twin in humans or mammals, where during egg development ... the egg has split into two but it hasn't completely separated," he said

"As it splits the development has continued on and there's been this fusion point between where the egg has spilt and that's been retained into later adult life."

Some people have suggested the prawn was caught near Japan and was affected by radiation from the Fukushima nuclear power plant.

But Ms Colton said the prawns were bought from a local bait and tackle shop.

"I'm not sure how far they get their supplies from, but somewhat local anyway, somewhere in Australia," she said.

Professor Jerry said it was unlikely the radiation would have caused for the deformity.

The double headed prawn is being preserved at Reef HQ.