since this thread poses a very "Seeweed-like" question, we best focus on EXACTLY the kind of fish the hooded wonder himself, Seeweed, would be:
indisputably, he'd be this little fella, known as the "candirú":
this Seeweed-like fish swims up the kahks of humans, entering the end of the shaft and swimming on in....... where it does all sorts of damage, apparently......