For the growth ? Its hard to say but i do have some storys in this area so i will share.
I bought a female ( thought it was male) FH in mar 07. By aug 07 she was 6". This was all in a 125 gallon though. Then by mar 08 she was right on the nose at 11". I trded her to a friend in may 08 and she breed with his male with in 2 days. thats ho i found out she was a she.
I had a pair of 2" FH in a 55 at the same time. They both got to 3 1/2 " in about a month then the breeding started and the male out grew the female by 3" in 3 months. So he was 6"+ and she was still 3 1/2 ".
The very first FH i had was a big knarly looking thing. He had a massive hump and big red eyes and 1" long teeth when he was 8" long. I had for about 4 months and he went from 2" to 8" in that time. Oh yea he was only in a 29 gallon by the way. I traded him when he hit 8" though as i did not have a larger tank to put him in.
After him I went into the army and had a Male From thialand. He was in a 55 gallon when i left for korea. He was only 3" long when i left in sept 03. I came back on leave in Jun 04 and he was 13". My wife did a very good job with him. He got traded while i was on leave.
All that being said I think they grow very fast. I also think a 75 gallon is min for one. A big male in a 55 would be very Crapped. a female would be as well. though most stay smaller then my exception. A 55 gallon should be fine for a growout tank though. Maybe yours could stay in there until it hit around 7" .
Good looking fish though. Take good care of it and it will reward you with a life time of aggression,LOL
