Electric Eels

In the present day environment of electric eels, they are surrounded by murky and dirty water, leaving them very dark in color and a bit smaller in size because of their difficulty searching for food. Due to the naturally murky water and dark habitat these vertebrates live in, they were born with something called a lateral line system, that helps them sense predators and prey, just by motion. After some time, the river these eels live in will clean up, and turn the water into a more clear and clean environment.  The adaptations these electric eels will develop over time would be them turning a lighter color due to more sun hitting them because of the water being clearer and being bigger in size because of the ability to be able to see and sense food easier.