When saltwater fish long ago evolved to live in fresh water, many of them also evolved a more sophisticated hearing system, including middle ear bones similar to those in humans.
Two-thirds of all freshwater fish today — including more than 10,000 species, from catfish to popular aquarium fish like tetras and zebrafish — have this middle ear system, called the Weberian apparatus, which allows them to hear sounds at much higher frequencies than most ocean fish can, with a range close to that of humans.
University of California, Berkeley, paleontologist...
