Cavefish are a fish typically found in dark freshwater caves. Surface dwellers need eyesight in order to survive, but when they migrated into caves this sense was no longer necessary. Mutations rendered some fish blind and the mutation flourished. A prime example of convergent evolution, unrelated cavefish species all over the globe independently developed this trait. Let’s take a look at some of the fascinating facts about these blind fish species.
Mexican Cavefish
The Mexican Cavefish is a blind fish species, yet it can view its surroundings by producing bursts of suction with its mouth. They feel the pressure waves as they bounce back and get a sense of distance. Their sense is similar to echolocation, the way that dolphins and bats use sound waves to detect objects.
Somalian Cavefish
Proving that cavefish do not need eyes to count, Somalian Cavefish can consistently find a bundle of six sticks. Scientists only placed food amongst groupings of six sticks. Even when they arranged less sticks to take up the same amount of space, moved the bundles, and used larger sticks that had the same density, the cavefish learned to routinely check the bundles with exactly six.
Tinaja Cavefish
The Tinaja Cavefish only needs to sleep for two hours a day, ten hours less than its surface dwelling relatives. Curiously, when interbred with the surface dwellers the offspring keep their eyesight and also sleep less. This research showed biologists that eyesight is the dominant trait in these fish.
Southern Cavefish
The Southern Cavefish is not just blind, but it is also deaf to high-pitched noises. Upon studying the caves that the fish came from researchers realized that the loudest sounds in the caves were high-pitched. The Southern Cavefish may have evolved to tune out these unessential sounds.
Hoosier Cavefish
A recently discovered cavefish species has been renamed after the Indiana University Hoosiers. Though the university is the birthplace of modern ichthyology, or the study of fish, it is still an odd distinction. After all, these species are different from most fish in that they are blind and their anus is near their head.
