You may consider your eyes a priceless commodity, but for Mexican cavefish, they were a burdensome expense. In a first-of-a-kind study, scientists have figured out exactly how much energy an animal saves by abandoning vision — in this case, anywhere from 5 to 15%.
Pictured above is a very peculiar fish that lives in a few North American caves. It looks very much like other fish, except in one respect: it has no eyes. The story of its adaptation to life in pitch blackness is one of the weirdest stories in evolutionary history.
To adapt to their eternally dark surroundings, Mexican cavefish have gone blind, lost their pigment, and changed their sleep cycle. You can see one in the photo up top. Here's the weird thing though...all those fish are the same species.