I had a Large Red Snake Head about 20 years ago in a 55g ( when they were legal). He got so big that when he would shimmy or bang the glass you could feel it across the room. I think he would have eventually broke the glass. He grew almost 18" in the 55 and we wound up putting him a 1000g tank at a local pet store. He grew to almost 3ft and was there for years. Of course now I would never place a fish that would grow that large in a 55g.