Clownfish are in the same family as damselfish but the two are separated into anemone fish (clownfish), and damselfish. Clownfish and anemones live together benefiting from each others company. They can be kept in and aquarium with or without and anemone but if you decide to keep and anemone you should make sure its special needs are met.
Most fish in this family can become territorial (aggressive) when they get older. They are brightly colored so they are a popular aquarium fish. There are around 360 species classified in this family, about 28 in the genera.
Clown fish can be overtly territorial, in particular where any threat to their host anemone is concerned. It is suggested that they be introduced with their host anemone after other fish tank mates, or provided with their own system. If your clown fish are very large and you want to try adding new specimens; disturbing/re-arranging the physical environment, extra-feeding and a watchful eye for problems are advised. Most other species of fishes are left alone as long as they are previously established, larger or more aggressive, and do not bother the Clown fish’s anemone or come too close while the clown's are breeding. Anemone fish can and will attack you and draw blood if so inclined.
Large non-paired adults generally do fight in all but the largest aquaria. Likewise, mixing species of all but juvenile sizes is chaotic. Keep them in separate systems.
To reiterate; aggression can be intense amongst and between species of Anemone fishes. They lock jaws and "bite" each other cichlid-like. To reduce agonistic behavior, provide adequate size quarters, a number of anemones, be leery of mixing sizes and sexes and restrict your collection per tank!. If you want to try mixing adult species, make sure each pair has a large anemone, so they won't fight over anemones. Breeder pairs of some species are kept in ten to twenty gallon systems commercially; yours should be much larger.
Clownfish will eat almost everything that is offered to it. It should be fed everything: live foods, algae, frozen foods, and flakes. The minimum tank size recommended for this fish is 30 gallons. Their maximum size is about 5 inches. Anemone fishes are sensitive to chemical and physical conditions and changes.
Maroon Clown fishes can be, become mean, particularly if crowded, especially if placed with other fishes, clownfish species included, that will not "back down", recognize their obvious superiority. Some folks try to diminish this tendency to "rule all" in their Maroon tanks with the addition of anemones, more decor this almost never works.