I introduced 12 at one time and got lucky. Another tank of mine has 8 jumbo and little to no squabbles. In the clownfish world, size does matter. But, it's not what you think. For clownfish, the females are larger than the males. So if you have a large clownfish or a clownfish that has been alone for a long period of time, chances are that it is a female.
Female clownfish are much more dominant than their male counterparts. They greedily try to eat most of the food that gets into the tank (which is one reason the males don't grow as large). They will often aggressively protect their "home", whether that be an anenome, a nesting site, a clay pot or the entire fish tank. If it attacks your hand when you're trying to clean the glass or it won't let any other fish near its spot, you most likely have a female clownfish.
Then comes who's the boss. The female rules in most cases. This is how the social hierarchy works for clownfish: There is one dominant female clownfish, partnered with a male, who is the next most dominant fish. The female is larger (often much larger) than the male. Next are non-mating males and juveniles. They are usually smaller still than the dominant male. If the male mate were to die, the next dominant male would become the mate (if the female accepts him). If the female were to die, then the dominant male would change to female and the next male in line would become the mate.
Of course, that is in a perfect world, the open reef. In our tanks it is not always that simple. If you introduce two fish at the same time then one will likely become the female and the other male. This does not guarantee that they will mate. You will be able to tell which is the female because she will be much more aggressive. Often, the female will barely let the male eat and sometimes will almost control where in the tank the male is allowed to go. This unfortunately in many cases will go on until the male submits or is killed by the female.
