Don't know how fast excatly...but i would assume fast like most other cats. At least one inch every two months, maybe more. I've seen two foot plus ones before.
a "blue channel" is the actual hybrid between a blue and a channel catfish, most people just call a channel cat blue channels because of the hybrid strain. The hybrid and the normal variant of the channel catfish both grow the same. 3'-4' and yes they can reach every bit of that in captivity. They grow extremely fast. Mine grows faster than my rtc currently is almost 21" after a year.
i wish my cam was working. my baby is a 36ish and he's about 2.5 years old. on the other hand tho, i have a 1 yr old who hasn't broken 6" yet. it depends on the size of your tank. i do believe that cats grow in correlation to tank size when the water is kept at a cold enough temperature. my tank is at a year round 65 degrees. my older tank was room temperature avg. my cat now is in a 600 holding tub i got from my college
I kept a blue channel cat when i lived in Florida,got him at 6 inches,he outgrew the 100 gal tank he lived in in about 8 monthes,so yes they are VERY fast growers and always VERY hungry!!!