The emergence of fish on to land was a pivotal transition in evolution.
Now scientists have attempted to re-create it in a remarkable experiment, in which 100 fish were reared from birth on land.
The study used an African fish, the polypterus, that has lungs and can “walk” between pools, but normally spends its entire life in water. The creatures survived “happily” out of water for nearly a year, suggesting ancient marine creatures may have made the leap to land more readily than previously thought.
Emily Standen, who led the study at the University of Ottawa, said: “I wasn’t thinking, ‘Oh my God, we’re going to kill all these fish’, but I was definitely prepared to have to rescue them. Actually they were very happy.”
The findings bring scientists closer to answering the question of how, about 400 million years ago, fish evolved into tetrapods, the evolutionary branch that gave rise to amphibians, reptiles, birds and mammals.
Dr Standen and her colleagues turned to the polypterus, an elongated fish with large front fins that lives in swampy African rivers. It resembles some varieties of fish that appeared on the fossil record about 385 million years ago, when scientists believe the transition was taking place.
Previously, scientists have speculated that significant genetic changes might have been needed for early fish to survive out of water for long periods, but this study shows that even fully aquatic fish are extremely adaptable.
In the study, published in the journal Nature, the scientists raised 100 of the fish in an aquarium with wet floors and misters that kept the air humid. They showed no signs of stress, the scientists say, and fed normally — the standard test for a fish being content. After eight months, the land-raised fish were compared with 50 fish that had been kept in water.
The land-raised fish took faster steps, slipped less and held their fins closer to their bodies. When they moved, they held their heads higher and wiggled from side to side less. The fish also showed anatomical changes, including stronger chests and an elongation below the head, which could be interpreted as the beginnings of a neck.
The land-reared fish were no worse at swimming, suggesting there may have been no initial trade-off between being a good walker and an adept swimmer.
