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Prawns turn red in black buckets


Prawns try to blend in with their background so turn darker red in a black bucket (Image: iStockphoto)

Prawns turn a deeper shade of red if you dunk them in a black bucket of water for a few hours, say Australian scientists.

They say the prawns are trying to blend into the dark background, so change their pigmentation to match.

As the public tends to favour darker coloured prawns, this simple step will increase the market value of farmed prawns, says CSIRO's Dr Bruce Lee, who was speaking at a recent conference in Sydney.

It may also make the prawns more nutritious as the darker pigment is a type of antioxidant, the scientists say.

"This was pretty much a fortuitous discovery," says Lee, director of CSIRO's Food Futures Flagship.

He says CSIRO researchers involved in improving the texture, flavour and size of farmed prawns happened to leave some in a black bucket one day while they were changing the tank water.

About 3 hours later they noticed the prawns had turned dark red, a feature that attracts a market premium of between A$2-4 per kilo.

Prawn colour depends on the distribution of pigments called astaxanthins in the outer body layer and shell.

Prawn farmers include astaxanthins in feed to increase the darkness of their catch but they can now get darker prawns than before and spend less on adding astaxanthins to feed, the researchers say.

All they need to do is place prawns in a black tank before harvesting them.

Colour changes elude predators

Lee says prawns change their body colour to fit in with the darkness or lightness of their surroundings to escape predators.

By dispersing or concentrating the pigment and by manipulating the chemical structure of the pigment, the animals can control how visible they are.

"We believe that's what's happening in this case," says Lee.

The researchers also believe the astaxanthins may have similar nutritional benefits to antioxidants.

Lee was speaking at the recent Future Directions Food Safety Conference in Sydney.

Tags: environment, agricultural-crops, biology