How to Pair Clownfish
Clownfishes, like many saltwater aquarium fishes, have the ability to change sex, and this is critical information for anyone considering keeping more than one in most saltwater aquaria. Clownfishes are what are known as protandrous hermaphrodites, which means the most dominant fish in a group of clownfish of the same species becomes a female. While interspecific jockeying for pecking order amongst a group of maturing clownfish is normal, the aquarist needs to understand that two mature females (or a dominant, established female confronted with any sex fish of the same species) may well fight to the death. Once a female, a clownfish will not revert back to being a male.
It generally takes between a year and two years for a clownfish to reach sexual maturity. At that point, the fish will remain immature or will transform into a male or female fish depending on social stimuli. For example, if a sexually immature clownfish is kept by itself, it will remain sexually immature or become a female when it reaches sexual maturity. If that fish is kept with other clownfish of the same species, however, its transformation will be dependent on the other fishes in the group. Because the dominant female will pick on any fish that may appear to threaten her dominance, many fish in the group will remain immature or become male in order to not attract aggression. If the dominant fish dies or is removed, the next most dominant fish in the group will take its place, changing sex to a female if necessary.
There are several ways to pair two clownfish in an aquarium. We encourage people who want to keep two clownfish together in the same aquarium to either acquire a mated pair or acquire two small juvenile clownfish of the same species at the same time. It is best if one of the juvenile fish is larger than the other, but both must be juveniles. When two small juvenile clownfish are added to the aquarium at the same time, they will sort out their own relationship to one another as they mature. Once they reach sexual maturity, one fish will become the dominant female fish, and the other fish will be the submissive male. Because they were able to mature together without additional social stimuli from other fish of the same species, the jockeying for dominance between the two should never become intense enough to kill the subordinate fish. In many cases, this is, in our opinion, the best way to pair clownfish.
You will know the two fish have become a pair when they are seldom seen far from one another. They should host in the same anemone or, in the absence of an anemone or other suitable host, they should occupy the same general area of the tank. A clownfish pair is different than two clownfish that have simply accepted one another's presence in the aquarium, although this "acceptance phase" is usually a step toward a pair bond. Once successfully paired, the two clownfish should begin to spawn. Once this happens, you are well on your way to breeding your own fish, but that's another article.