[Fishy or not, it is a beautiful romance that they can only hope to have one day. Or, well, Armin at least. Krieg isn't one for romance much, is he?]

They don't. For the most part, Sharpedo live alone. Though they do school together to take on big prey. With enough of them there, they can even take down a sick or injured Wailord. Assuming the pod is not nearby.