Margined Butterfly (Chelmon marginalis)

The Margined Butterfly (Chelmon marginalis) known to tropical fish keeping enthusiasts as the Western Beaked Butterflyfish, Willemawillum, Three-Stripe Butterflyfish, Marginalis Butterflyfish, and Margined Coralfish is endemic to Australia and ranges from the Houtman Abrolhos in Western Australia, around the coasts of northern Australia to the northern Great Barrier Reef, and the reefs in the Coral Sea off Queensland, Papua New Guinea, and Vietnam.

The Margined Butterfly is a solitary species that is usually encountered alone, or in pairs along the outer slopes, drop offs, and islands of their range on coral and rock reefs where they prey on crabs, shrimp, polychaetes, and other benthic invertebrates.

Margined Coralfish are found in shallower waters around the islands, as well as on the deeper drop offs along the outer slopes at depths to over 100 feet.

Margined Butterfly (Chelmon marginalis)

The Margined Butterfly has a silvery white body with two slender, vertical orange bars edged in black at the front part of the body, and a wide yellowish or yellowish orange band edged in black at the caudal peduncle. The first bar at the head intersects the eye, and the second wider bar is an extension from the edging on top of the dorsal fin, down in front of the pectoral fins and into the pelvic fins which have a splash of yellow.

Chelmon marginalis closely resemble Copperband Butterflyfish (Chelmon rostratus) without the mid body stripe, and the Muelleri Butterflyfish (Chelmon muelleri).

Juvenile Chelmon marginalis have an ocellus on their dorsal fin and a posterior bar that

Juvenile Margined Butterfly (Chelmon marginalis)

disappears as the fish mature into adults.   Adults lack the false eyespot.

The Margined Butterfly can be housed singly, in pairs, or in small groups if all specimens are introduced at the same time, in a mature FOWLR aquarium of at least 125 gallon capacity with a coralline gravel or sand substrate, large amounts of live rock arranged into crevices, caves, and overhangs for them to hide and graze among, and plenty of free swimming space.

Because Margined Butterfly pick on Tridacna clam mantles, corals, tubeworms, and eat Aiptasia, a variety of benthic invertebrates, crustaceans, the heads of feather dusters, some soft corals, and will decimate polychaete worm populations; they are not considered reef safe.

Like Chelmon rostratus, Chelmon marginalis are sensitive to changes in water quality and require an efficient filtration system, protein skimmer, and wave maker to simulate their turbid environment.   They prefer temperatures in the 73-81° F range.

Margined Butterfly are generally peaceful however when housed singly or as a pair, they will battle over their territory with others of the same genus.

They can be housed with other peaceful species including Chromis, Cardinals (Pajama Cardinal), Clownfish, Damselfish, Firefish, Dottybacks, Gobies, and Dwarf Angelfish like the Bicolor Angel.

Margined Coralfish have not been bred in an aquarium environment.

In the wild, they form up into pairs during breeding.  Eggs are deposited into the water column by the female with the male immediately fertilizing them. The small, buoyant eggs hatch out into larvae called thoilchyths that have a bony plate over the head to protect them from predators. They remain pelagic until fully developed into juveniles.

In their natural habitat, Margined Butterfly are primarily carnivores that prey on benthic invertebrates such as crabs, shrimps, tubeworms, soft corals and polychaetes.

In an aquarium environment, they require a varied diet of live and frozen meaty foods including live fortified Brine and Mysis shrimp, live black worms (Lumbriculus variegatus), sessile invertebrates, live clam, black mussels, Angelfish preparations, sponge based marine preparations, flake foods containing Spirulina or Nori, and high quality marine omnivore pellets.

Margined Butterfly (Chelmon marginalis) are rarely seen in the aquarium trade.  They are occasionally available online from waiting lists to tropical fish keeping enthusiasts from a variety of suppliers and specialty fish shops at prices that vary according to size and area of collection.

Currently waiting list prices start at around $719.00 for 4.75″ specimens, to over $899.99 for larger Australian specimens.

Minimum Tank Size: 125 gallons
Aquarium Type: FOLR
Care Level: Moderate
Temperament: Peaceful
Aquarium Hardiness: Moderately Hardy
Water Conditions: 78° to 83 °F, dKH 8 – 12°, pH 8.1 – 8.4, sg 1.020-1.025
Max size: 7″
Color Form: White, Black, Orange, Yellow
Diet: Omnivore
Compatibility: Reef with Caution
Origin: Australia, Great Barrier Reef Queensland
Family: Chaetodontidae
Lifespan: 5-10 years
Aquarist Experience Level: Intermediate