Clown triggers -- or clown triggerfish -- are large, striking fish who can grown up to 20 inches long and have large white spots all over their bellies. Due to their size, adults require tanks with capacity of at least 300 gallons. They're known to be aggressive, so finding suitable tank mates can be hard. In many cases, it is safest to house them alone and eliminate risk.
Juvenile Clown Triggers
Juveniles clown triggers are different than their adult counterparts in that they will often live peacefully in a community tank. They'll often get along fine with fish more peaceful than themselves, such as large angelfish, rabbit fish and surgeonfish. This social demeanor rarely lasts beyond juvenile stage, so you should have alternative living quarters ready for your clown trigger. No specific age at which these fish start becoming less agreeable is known, so keep a close eye out for signs of aggression to stop a clown triggerfish from hurting your other fish.
Who to Avoid
As a strict carnivore, the clown trigger will eat any fish he can fit in his mouth, so never house yours with a fish significantly smaller than him. The clown triggerfish is highly aggressive, so even large, peaceful fish are likely to get bullied or attacked. Invertebrates make up much of the wild clown triggerfish diet, so it isn't wise to keep him with any kinds of crustaceans, urchins, sea stars or mollusks. They don't get along with others of their own species, even.
Compatible With Corals
While the clown trigger's taste for invertebrates makes him unsuitable for the average reef tank, corals -- especially soft corals -- are usually a compatible addition to his aquarium. However, it is best to keep an eye on your triggerfish, as some individuals will take chunks out of corals. The clown triggerfish also has a tendency to rearrange rocks and plants in his habitat, so there's the chance that he will damage your coral by dropping rocks onto it.
Aggressive or Belligerent Fish
If you want your adult clown trigger to have a tank mate, another large and aggressive or belligerent fish is the only option. Only these kinds of fish will be able to stand up for themselves against your clown. Some possible choices include dampiera dottybacks, other aggressive triggerfish species -- such as orange-lined triggerfish, larger species of wrasse, large groupers or the most aggressive surgeonfish -- such as sohal surgeonfish or lined surgeonfish. The larger the tank you provide them, the less likely they are to fight with one another.