Pangasius catfish, the common ones like ID sharks, grow pretty fast I'd say 1-2" a month if fed properly and allowed enough space to grow. Pangasius Gigas grows much slower only maybe 1" a month if that and aren't available in the US legally.
If you're just inquiring about their growth rate, great. But if you're thinking about buying one, the smallest tank I'd start with is a 240 gallon which will be good for a year or year and a half tops. This species needs lots of swimming space and will get 2ft+.