There is a specific species of fish that can actually climb waterfalls with their mouths.
The Nopili Rock-climbing Goby is only an inch long, but often naturally completes a feat equal to a human running a marathon. That would be crawling up a 100-foot waterfall.
How they did this was unknown for a long time, but now we know they use their mouths!
Not only does it climb with the same thing it eats algae with, but it does it in the same way!
The sucking motion it uses to eat the algae is the same suction that it uses to get up those steep rock walls, according to Richard Blob, an evolutionary biologists at Clemson University.
This is an example of a known evolutionary phenomenon known as exaptation, in which a species will "take a structure or behavior and co-opt to do something totally different."
The classic example of this is bird feathers, says Blob. Feathers “may have evolved as an insulation structure before they were co-opted, or exapted, with some evolutionary changes for use in flight."
What the original use for the sucking of the Nopili Rock-climbing Goby is still unknown. Whether it was for the algae or for rock-climbing, the fish has found the perfect use of its own skills.