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By Bob Goemans
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Chaetodon

Chaetodon mertensii

Cuvier, 1831

Merten's Butterflyfish, Atoll Butterflyfish, Orangetail Butterflyfish

Likely Reef Tank Suitable

Likely Fish-Only Tank Suitable

Range: Western Pacific Ocean: East Africa to the Tuamotu Islands, and north to the Philippines and Southern Japan.

Size: 5 inches (12 cm)

Natural Environment: Inhabits lagoon reefs, reef faces, and slopes at depths between 10 – 400 feet (3 – 120 m) and mainly feeds on algae, stony coral polyps and various benthic invertebrates.

General Husbandry: Quite attractive as it has a white body with numerous chevron shaped grey lines, black eye band that is edged in white, a black crown also edged in white, with the posterior of the body and adjacent dorsal and anal fins a yellowish orange.

Best maintained in larger peaceful fish-only aquariums, especially those with lots of open swimming space, live rock hiding places, and having some micro and macroalgae growths. As to diet, a meaty diet of live fortified brine shrimp and/or black worms (Lumbriculus variegatus) is a good beginning. Once feeding regularly, various frozen meaty foods such as mysis, can be offered several times daily.

Even though basically a meat eater, there’s evidence it also injests some algae in the wild, therefore, flake foods, especially those containing Spirulina and/or Nori should also be occasionally offered. Not a difficult species to get feeding in captivity.

Should there be a problem getting this species to feed, small human consumption clams/black mussels purchased in local grocery stores and placed on the half-shell in the aquarium may help entice it to begin feeding. Over time, frozen foods like mysis and brine shrimp may be more readily accepted.

Its recommended there is only one species from this genus in the aquarium, as they tend to develop aggression toward others of the same genus.

Taxonomy:

    Order: Perciformes

    Suborder: Percoidei

    Family: Chaetodontidae

    Genus: Chaetodon

FYI: This species is almost identical to C. madagaskariensis, which inhabits the areas from East Africa including Port Elizabeth, South Africa to the Cocos-Keeling and Christmas Islands, north to Sri Lanka.

Pressing some soft foods into openings/crevices on a piece of old dead coral skeleton can sometimes encourage finicky eaters to begin feeding.

Experience Level: Intermediate

Temperament: Peaceful

Diet: Carnivore

Coral Safe: No

Invertebrate Safe: No

Acclimation Time: 30 minutes+

Aquarium Environment: Fish-only aquarium

Tankmates: Peaceful or non-aggressive

Minimum Tank Size: 55 gallons

Temperature Range: 72 - 82°F (22 – 28°C)

Specific Gravity: 1.020 -1.026

pH: 8.0 - 8.5

 Chaetodon mertensii (Merten's Butterflyfish, Atoll Butterflyfish, Orangetail Butterflyfish)
Photo © Bob Fenner
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