Yes, that is a tuber, it does not need to be potted, just toss it into the aquarium, new plants and roots will sprout from it, in fact several of them.
As for the rest of the plant, I bet you can find individual crowns if you search hard enough and pull them out from the main plant. Small divisions can be potted in a Dixie cup with sand and placed in your aquarium. As for the biggest plant, give it to someone for postage in a warmer zone.
Cheers,
Sean