Well, the body of fish grows to the tank size, of course. But unfortunately for the fish, their organs grow t maximum size... that is, if they could, without dying premature. This is often seen in Goldfish, Pleco, Koi, and even some Oscars and Gouramis.
Breed for the breed, not for the money; the words any REAL breeder would understand.
You must know nothing in order to know all, for all is nothing and nothing is for all.