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    Avoid for beginners

    Harlequin filefish

    Oxymonacanthus longirostris

    Also sold as Orange spotted filefish, Longnose filefish

    Not for beginners

    Harlequin filefish (Oxymonacanthus longirostris), photographed in the sea or an aquarium
    Photo: Diego Delso, CC BY-SA 4.0, via Wikimedia Commons
    Care level
    Advanced
    Adult size
    12 cm
    Minimum tank
    400 litres
    Temperament
    Peaceful
    With corals
    Not reef safe
    Captive-bred
    Wild-caught (captive-bred rare)
    IUCN status
    Vulnerable
    Show volumes in

    How do you care for the harlequin filefish?

    Peaceful; shy.

    Feeding

    Acropora polyps.

    A large share die soon after import; some can be weaned onto frozen foods while fed live coral.

    Tank and special needs

    Plan for at least 400 litres of water (the care sheet says 106 US gallons).

    Low flow; live Acropora food supply.

    Corals and invertebrates

    Eats Acropora polyps; obligate corallivore.

    Which tankmates suit the harlequin filefish?

    Only with peaceful fish; needs live Acropora.

    Suggested order in a mixed tank: add after the first peaceful fish.

    More than one harlequin filefish

    Only as a mated pair, or two juveniles added together. A third harlequin filefish is usually driven out.

    Other fish

    Checked against the other 59 fish in this guide, assuming a tank big enough for both. Individual fish differ, so treat this as a starting point.

    Take care (3)

    • Maroon clownfishMaroon clownfish is aggressive and may bully the harlequin filefish, especially if the bully is added first.
    • Humbug damselHumbug damsel is aggressive and may bully the harlequin filefish, especially if the bully is added first.
    • Powder blue tangPowder blue tang is aggressive and may bully the harlequin filefish, especially if the bully is added first.
    Usually fine together (56)

    Invertebrates

    Only the invertebrates with a known risk are listed.

    Avoid together (1)

    Take care (2)

    • Tiger tail sea cucumberA stressed or dead tiger tail sea cucumber can release toxins that harm fish; cover pump intakes.
    • Sea appleA stressed or dead sea apple can release toxins that harm fish; cover pump intakes.

    Corals and anemones

    Only the corals and anemones with a known risk are listed.

    Avoid together (2)

    • AcroporaHarlequin filefish feeds on Acropora and will strip them.
    • Acropora milleporaHarlequin filefish feeds on Acropora and will strip them.

    Take care (1)

    These checks follow the reasons fish and invertebrates clash: same species or genus, similar shape, mouth size, temperament, food, burrows, tank size and the order they are added. Individual animals differ; every source agrees on that.

    Quarantine and health

    Poor survival in quarantine without coral food.

    New fish are the most common way disease gets into a reef tank. Quarantine every fish in a separate tank before it joins the display, and choose a method that suits its tolerance of copper.

    Captive-bred or wild?

    Wild-caught.

    IUCN Vulnerable per FishBase; coral-dependent and declining with coral bleaching. Do not buy unless set up to feed coral.

    Sources

    1. Web page at fishipedia.frRead 21 October 2026, search summary only. Used for: tank, survival.
    2. Reefs.com articleRead 21 October 2026, search summary only. Used for: diet study.
    3. FishBase species summaryRead 21 October 2026, read in full. Used for: max length, IUCN VU.

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    Moorish idol

    Zanclus cornutus

    Not for beginners

    Care
    Advanced
    Adult size
    23 cm
    Tank from
    473 litres
    Temperament
    Peaceful
    Corals
    Not reef safe

    Photo Diego Delso, CC BY-SA 4.0

    Copperband butterflyfish

    Chelmon rostratus

    Not for beginners

    Care
    Advanced
    Adult size
    20 cm
    Tank from
    492 litres
    Temperament
    Peaceful
    Corals
    Reef safe with caution

    Photo Luc Viatour, CC BY-SA 3.0