Washington, Oct 25 : Prehistoric fish that made their first foray onto land probably saw their new environment in full colour, a new study by Australian researchers from the University of Queensland, Brisbane, has revealed.

The scientists led by Helena Bailes analysed the retinas of the Australian lungfish (Neoceratodus forsteri) and compared them to those of other fish and amphibians.

Findings revealed that the DNA of five visual pigment (opsin) genes in the retinas of lungfish were more in common with four-legged vertebrates (tetrapods) than with fish retinas.

The lungfish is thought to be the closest living relative to the first terrestrial vertebrates. Although they take in oxygen mainly through their gills like most fish, they can also breathe air if water quality is poor.

Lungfish were previously thought to have poor eyesight due to their small eyes, low spatial resolving power, sluggish behaviour in captivity and ability to detect prey using electroreception.

N.forsteri, however, inhabits a brightly lit, shallow freshwater habitat similar to the environment from which terrestrial evolution probably occurred, the researchers found.

This prompted the team to investigate the complement of opsins expressed in N. forsteri, to trace photoreception's evolution in ancestral tetrapods.

Lead author, Bailes said, the study had paved the way for behavioural work with lungfish to see if they could discriminate between objects based on colour.

“The genus Neoceratodus, of which N. forsteri is the sole survivor, is found in the fossil record from the Lower Cretaceous period 135 million years ago and therefore N. forsteri lays claim to being the oldest surviving vertebrate genus,” said Bailes.

“The visual system of N. forsteri may represent an evolutionary design most closely reflecting that present just prior to the emergence of land vertebrates in the Devonian period,” she said.

The study appears online in the journal BMC Evolutionary Biology. (ANI)