Know one really knows.. The largest recorded one was an 18"er we Imported a few months back. They are really awesome and personable fish.. They don't require alot of swimming space, so I would imagine would could live happily in a 75-90g tank for life, maybe a 125 eventually.. They will definately be the 'talk of the tank' when people come to your house!! People LOVE this guy in our shop..thefishofdoom said:how big dose the knife get