Harlequin filefish

1) Where they come from

Harlequin filefish (Oxymonacanthus longirostris) are little coral-reef specialists from the Indo-Pacific. You’ll usually find them hanging around branching Acropora on shallow reefs, basically living in and on the coral like it’s a condo and a buffet at the same time.

That natural lifestyle explains almost everything about why they’re “expert” level in our tanks: they’re picky eaters, easily stressed, and they don’t love chaotic reef setups with pushy neighbors.

2) Setting up their tank

Think calm, mature, and predictable. I’ve had the best luck putting them in a well-established reef (months old, not weeks) where pods and micro-life are already everywhere and parameters don’t swing.

• Tank size: I’d call 40–55 gallons the practical minimum for a single, 75+ if you want a pair and less drama.
• Mature rock: lots of hiding nooks and a “maze” feel so they can duck out of sight fast.
• Flow: moderate, not a washing machine. They like to pick and peck without getting blasted.
• Lighting: whatever your reef runs, but avoid sudden changes. They spook easily.
• Stability: steady salinity and temp matter more than chasing a specific number.

Cover your tank. They’re not famous jumpers like wrasses, but stressed filefish can launch, and you’ll be mad at yourself when it happens.

3) What to feed them

This is the make-or-break part. In the wild they pick coral polyps all day, and a lot of new imports either refuse “normal” foods or take forever to convert. Some individuals transition nicely, some never do.

• Start with small meaty stuff: enriched brine shrimp, mysis (small/medium), chopped clam, roe, finely chopped shrimp.
• Frozen blends can work if they’re not huge chunks. Think “tiny bites” not “predator cubes.”
• Live foods help a lot early on: live brine, copepods, blackworms (if you can source them safely for marine use).
• Feed many small meals. I’m talking 3–5+ times a day at first if you can swing it.

If yours is already eating frozen, protect that habit. Keep a routine. Same spot, same tool, same timing. They’re weirdly comforted by predictability.

4) Behavior and tankmates

They’re gentle, a little shy, and kind of “hover-y.” They’ll weave around branches and rock like they’re looking for the next bite. They’re not fast, and they don’t like being harassed.

• Good tankmates: calm gobies, small blennies, peaceful wrasses (not hyper ones), chromis that aren’t bullies, cardinalfish.
• Risky tankmates: aggressive clowns, dottybacks, hawkfish, big wrasses, triggers, puffers—anything that makes feeding stressful.
• Watch out for food hogs: tangs and anthias can outcompete them even if they’re not “mean.”

You’ll know they’re settling in when they stop doing that constant “nervous hovering” in the corners and start picking around like they own the place.

5) Breeding tips (the fun part)

People do breed them, and watching the courtship is awesome. In home tanks you’re most likely to see pair bonding and spawning behavior if they’re well-fed and not stressed by tankmates.

• Keep them fat and comfortable: frequent small feedings and low competition.
• They like structure: branching coral or dense rockwork where they can “claim” a little zone.
• If you see spawning, the eggs/larvae are the hard part—rearing is a serious project (live foods, cultures, time).

6) Common problems to watch for

Most losses come down to starvation or stress. These fish can look “fine” for a couple weeks while slowly running out of steam, especially if they’re not actually swallowing much.

• Not eating (or fake-eating): they peck at food but don’t take it in—watch the mouth and chewing.
• Weight loss: hollow belly, pinched head, and that “paper thin” look from the side.
• Getting bullied: torn fins, hiding all day, refusing to come out at feeding time.
• Disease after import: ich/velvet can hit them hard because stress lowers their resistance fast.

My honest rule: if you can’t commit to multiple small feedings a day for the first month (and you don’t have a stable, mellow reef), hold off. But if you can meet them where they’re at, they’re one of the coolest, most personality-filled little reef fish you’ll ever keep.