Have a spotted and striped raphaels catfish, also an irwini. All 3 I think grow fast, according to my specimens. The irwini in 1month have grew by about 2inches. The striped one is now 6inches, from 1 that was about 1 and a half incher 5mths back. The spotted one is now 4-5inches from about the same size as the striped within the same period of growth. I have another striped 1 in my community tank which is an extreme slow grower, bought 7mths back at the same size and now its less than 3inches. So my guess is either specimen characteristics or the place they are kept in. The small striped is in a densely planted tank while the large 1 is kept in a tank with more free roaming spaces