Sydney, Feb 12 (IANS) Most people wouldn't give a second thought to the inner workings of the fish eye. But research by University of Queensland (UQ) scientists is unlocking the secrets hidden behind these fishy lenses.

Justin Marshall, professor and colleagues from the Sensory Neurobiology Group of UQ Brain Institute, have found for the first time how certain types of fish see colour.

Marshall's work revolves around the role double cones play in the vision of trigger fishes.

Cones are light sensitive cells in eyes that allow us to see, and double cones are two such cells fused together.

'It has been suggested that double cones are used for achromatic (non-colour) tasks such as luminance, motion and polarisation vision,' Marshall said.

'This is the first direct evidence that individual members of double cones are used in colour vision as independent spectral channels.'

He said while the eyes of most vertebrates including fish, frogs, reptiles and kangaroos are packed with double cones, their function was not previously known.

'These photoreceptors are not present in human retina or other placental mammals and, perhaps as a result, we have overlooked the fact that we do not know what they do,' he said, according to a university release.

'The discovery that reef fish use double cones for colour vision solves a centuries old mystery.'

The research, a collaboration between UQ researchers and Misha Vorobyev from the University of Auckland, was published in Biology Letters.