Well, as a present tense verb, you could say "TumbleWeed fishes along the dock every day"
But not as a noun! Even if you look it up, "fishes" is not the plural. Fish is. We in Canada speak ENGLISH. Jk, I understand you all do as well.
Ok but Berry it seems to be lost on you that he's speaking like a pirate or weathered fisherman. You can't count on them for proper grammar. If you imagine him saying it in the stereotype pirate voice, it makes more sense :)
Fishes is what it is supposed to be, people such as scientists say fishes. But over time people have thought it is fish and started saying that, like people saying "I swam a lap" when its supposed to be "I swum a lap"...
They will, and that's perfectly cool. Otherwise, the items lose all worth completely :3
This way, they're still slightly valuable. For example, sculpty blocks are still 1-2c each, despite being craftable