a lot depends on witch sp. you have. if it has the tail streamer. it should stay clamer and not get as big. no streamer chances are great of a massacre or your tankmates could have eaten the streamer off so it is the calmer one and you just don't know it. the calmer one is more commonly available so you have a good chance that it the one you got. i can remember the scientific name of the sp. but it starts with a "h" for the calmer one and you can tell the diff by the streamer.
well he is hemibagrus wyckiodes and he has grown up with a lima same size as it and pleco's ,2x small syodontis 2-3",flag tail 8"
cheers people i will keep good eye on him (if need move to large tub pond i can bring in)