you can put a 100 in ther it all depends on how much water you are willing to change. Also you can fit 3 cons in there which are comfortable. Any more it gets a little testy depending on male or female. I would say 4 females might work out. Though you can put say 8-10 in there and make it " Japanese Style" lol.
honestly it's not about quantity... it's quality...
the more fish you stuff inside the lower the potential quality of life it is gonna be... stress will increase, your fish waste will increase... and your headaches will increase as well.