Of course fish don't eat quarters! Or at least they aren't supposed to . . . but this sign isn't quite clear on the subject.
Maybe there is one specific fish that likes to eat quarters? Like one of those deformed fish from the Amazon? The kind that look like they spent too much time in radiation infested waters?
Now obviously they mean for you to bring quarters to buy their fish food to feed the fish.
Or maybe not, it's unclear. :)