They do get big over time. The species max size is 17 inches, but the biggest I have caught was around 10-11''. They are a very fun fish to have and I don't like recommending 55's, you would be ok for a while, but bigger is better and you would be way better off with a little more width. Something like a 75 or a 90 would be great!fishkeeper1;1957852; said:if i got a rock bass could i keep it in a 55 or 60g? idk why but i love rock bass but theres none by me