clown grow really slow, but then they grwo up they can be like 8-10", ive never seen them over like 8" but when they are that big they are kinda of aggressive. ive seen them chase other smaller fish away like some small neon tetras and cardinals too. this was in an LFS 250g tank with like 10 clown freom 3" up to 8" and with neons, cardinals, some bosemian (sp?) rainbows and gouramis.