Teaching A Fish To Walk

by Dish Staff

Carl Zimmer unpacks a fascinating new study on bichirs (a type fish that “mostly live in lakes and rivers” but “will sometimes crawl across dry land with their fins”):

McGill scientists wondered what would happen if they forced the fish to grow up out of the water. To find out, they reared eight bichirs in a terrarium with a pebble-strewn floor. To prevent the bichirs from drying out, the scientists installed a mister to keep their skin moist. The fish grew for eight months, clambering around their terrarium instead of swimming.

Then the scientists examined these fish out of water. They found that eight months on dry land (or at least moist land) had wreaked profound changes to the bichirs.

For one thing, they now walked differently. Overall, they were more efficient. In each step, they planted their fins on the ground for less time, and they took shorter strides. Instead of flapping their fins out to each side, they placed their fins under their bodies. Their fins slipped less when they pushed off of them. They made smaller movements with their tails to go the same distance as a bichir raised underwater. Aquatic bichirs walk on land with an irregular gait. The terrestrial bichirs, on the other hand, walked more gracefully, planting their fins in the same spot relative to their bodies time after time.

Noah Baker adds that, beyond the fishes’ new walking style. “their bone structure and musculature changed to be more suited to a walking lifestyle”:

The results provide evidence for developmental plasticity, in which organisms alter their anatomy and behaviour in response to environmental change. The team suggests that this process, as demonstrated by the bichir, could have given the earliest tetrapod ancestors the ability to venture onto land. In doing so, claims [lead author Emily] Standen, they would have become exposed to the selective pressures of a terrestrial environment, thereby speeding up the evolutionary transformation from fins for swimming into limbs for walking.