A walking fish is not something that people think of when they think of aquatic animals, but researchers from Canada have decided to raise fish on land and the experiment has something to do with evolution. The researchers wanted to learn what changes might have taken place when ancient and now-extinct species of fish crawled from the sea and eventually evolved to become land-living creatures.
For the study published in the journal Nature on Aug. 27, Emily Standen, from the University of Ottawa in Ontario, Canada, and colleagues raised a group of dragon fishes in a terrestrial but damp environment and another group in an aquatic environment.
The fish, which is formally known as Polypterus senegalus, has lungs and gills which gives it the ability to breathe on land. It can also use its fins to crawl. It isn't the only fish that can crawl using its fins but it is the closest known living relative of the ancestors of limbed vertebrates and ray-finned fishes that make up almost all the living fishes today. Studying it could give insights on how sea creatures evolved to become land animals.
After eight months, the researchers tested the walking abilities of the fishes and found that those that were raised on land were far better at walking compared with their counterparts that were raised on water. The terrestrial dragon fishes had faster and more consistent steps and could hold their heads higher. They also held their fins closer to their body's midline and did not slip as often as their water-dwelling counterparts. The researchers also noted that most of the changes that occurred to these land-raised fishes were those that gave their head and fins of additional room to move about.
"It's an important change, because if you think of a terrestrial lifestyle," Standen said. "You actually need a neck on land because you're stuck on this plane, and you need to have more head motion that's independent from the body."
In essence, the fishes appeared to have responded and adapted to the demands of their environment, a phenomenon known as "developmental plasticity", which could have happened to the fishapods that became the first tetrapods on Earth.
"Here we show the remarkable correspondence between the environmentally induced phenotypes of terrestrialized Polypterus and the ancient anatomical changes in stem tetrapods," the researchers wrote. "Our results raise the possibility that environmentally induced developmental plasticity facilitated the origin of the terrestrial traits that led to tetrapods."