Of technicolour lungfish

The colourful world of living fossils

The Australian lungfish, often described as a living fossil, has probably been living in a world of blazing colour since before the dinosaurs arose.

Research from the University of Queensland has identified genes for five colour pigments, despite the fact that vision was always assumed to be of little importance to the fish. By contrast, humans can only detect three pigments - red, green and blue.

Colour vision is controlled by photoreceptors in the retina called cones. Rods handle the night vision. Lungfish still retain five kinds of cone including two that have been lost by mammals. The lungfish's cones are also tuned to longer wavelengths than in other fish, according to postgraduate researcher Helen Bailes.

"We keep discovering ways in which these animals are quite different from other fish," she says. "Their eyes seem designed to optimise both sensitivity and colour vision with large cells containing different visual pigments."

For instance, the photoreceptive cells, which house the visual pigments, are bigger in lungfish than for any other vertebrate, probably making them more sensitive to light.

"Lungfish are very large, slow-moving fish, so vision was always assumed to be of little importance. This work may change that theory."

The Australian lungfish is the most primitive of the living lungfish, a species that has survived for over 100m years, thus earning the name living fossil.

They are important because they are the closest relative of the first creatures that left the seas and began to colonise land for the first time. This makes them the best indicators of what life was like for one of our earliest ancestors.

Bailes now hopes behavioural research can find out how these fish are using their eyes for colour vision in the wild. ®