One of the most frequently asked questions we get is “how many clownfish will fit in a ________ gallon aquarium?” The real answer to this is not so much a matter of how many fish can fit, but how many of these fish should be housed together. For just about any aquarium of the minimum adequate size or larger, we do not recommend adding more than two clownfish, but even that has some important caveats. The two clownfish must be of the same species, and be careful in how they are introduced. Juvenile clownfish can be housed in groups, and often get along fine. But as they mature, the more aggressive individuals will harass others in the group, causing them to become injured, stressed, or even die. If you add a juvenile in with a mature, aggressive adult female, then you may or may not have success. It really just depends on the individual and certain environmental cues, and some trial and error will occur until a pairing is actually made. Clownfish of differing species will also fight with each other, resulting in nipped and torn fins, unnecessary stress, and eventually death.