there is no real rate, but they grow FAST-maybe a few inches or more a month. growth is based on diet, water quality, tank size, #of fish in tank, etc. you can put pictus cats, plecos, ropefish, or pretty much any large semi agressive chichlid/fish of the same water conditions as long as your tank is big enough. go to your lfs and see what you like, then do reaserch. just my opinion, but i like tiger oscars better. they look cooler. but its your choice.