" Most big freshwater fish, in most parts of the world, have all but disappeared from most places where they used to live. As with arapaima, the main reason is over-harvesting, but there are other factors too. Dams block the migration routes of many fish, so they disappear from the water above the dam — or even altogether, if breeding grounds are cut off. Draining of floodplains, cutting off backwaters, competition from invasive species and pollution also play a part. And sometimes it's just willful slaughter, as was the case with the North American alligator gar in the early 1900s, thanks to the incorrect assumption that killing these predators would boost populations of ‘game’ fish. "

― , How to Think Like a Fish: And Other Lessons from a Lifetime in Angling