Although fast growers I find this hard to believe.
You should check out my sticky above. I wrote if to answer as many question as possible so people don't have to ask the same questions over and over (no offense, I still find myself doing this at times) I always try to read stickies on fish because they're usually good reads with years of info and hundreds of sources compiled into a ten minute read.
They will grow 1-2" a week for the first couple months, then slow down to an inch a month usually when they hit 12". At this size they begin bulking up along with growing in length.