I had one go from 1" to 8" over the course of 6 months, so they have a pretty good growth rate, until it slows down when they hit about 10-12". Mine was in a pond with goldfish, and he liked to nip at thier tails so I guess don't keep it with colorful long-finned fishes.
I have one in with my GT and convict pair. He doesn't bother them too much. In fact, he pretty much doesn't even act like they are there. He seems to be a little slow growing but not bad.