1 billion, but they won't be alive
depends on what kind of fish, and what kind of filtration, and if you want a reef set up. If i had a 240, I would get a Volitan Lion, Gold Puffer, a Dragon Eel, and maybe just maybe a picasso if it and the puffer were purchased small at the same time(My freind had this combo in a 180, had to ditch the picasso) If Iwas going reef, I think Fish would be my after thought, If I was going community well........you could fit a whole heck of a lot of bangai in ther