If you're talking about Mbuna then 50 would be possible, but not with the oscar and JD in with them. Mbuna are very aggressive so it is a common practice to overstock to disperse the aggression so nobody gets singled out. If you are going to attempt to do this then you must have many different caves and hiding spots. That way everyone can have their own territory to defend. Excessive filtration and large water changes are also needed to handle the bio load. For example, my 110 has approx 30-35 mbuna and 5 clown loaches. For filtration I use a fluval 405, sunsun 304, and a magnum 350, as well as performing weekly 75% water changes.