Fish have evolved the ability to live on land many times, challenging the perception that this extreme lifestyle shift was likely to have been a rare occurrence in ancient times, new UNSW Australia research shows. "A fish out of water might seem an extraordinary thing, but in fact it is quite a common phenomenon," says study first author and UNSW evolutionary ecologist Dr Terry Ord. "Amphibious behaviour has evolved repeatedly in a wide diversity of present day fish, and the move onto land does not appear to be as difficult as has been presumed."

In the first study of its kind, Dr Ord and Dr Georgina Cooke looked at the evolutionary relationships of all living fish reported to be active on land. They also examined the environmental factors that might have promoted their emergence from the water.

The study is published in the journal Evolution.

The UNSW researchers found that 33 different families of fish have at least one species that demonstrates some terrestrial activity and, in many cases, these behaviours are likely to have evolved independently in the different families.

"These forays onto land have occurred in fish that live in different climates, eat different diets and live in range of aquatic environments, from freshwater rivers to the ocean," says Dr Ord, of the UNSW Evolution and Ecology Research Centre.

"While many species only spend a short time out of water, others, like mudskippers and some eels can last for hours or days."