Bristletail Filefish (Aiptasia-Eating Filefish)

1) Where they come from

Bristletail Filefish (Acreichthys tomentosus) show up across the Indo-Pacific on shallow reefs and rubble zones. They’re the kind of fish that likes nooks, algae-covered rock, and picking at tiny stuff all day. That “busy picker” lifestyle explains a lot about how they act in our tanks.

2) Setting up their tank

Give them a tank with rockwork they can weave through and a few calmer zones where food can drift by. They’re not strong, flashy swimmers like tangs—more like little underwater goats that want to browse.

I’ve had the best luck starting them in a stable, established reef (or reef-ish) system. A brand-new tank with swingy parameters and no natural “stuff” to peck at can make them sulky and hard to wean onto prepared foods.

• Tank size: 30+ gallons works for one, but bigger is easier if your tank has boisterous fish
• Aquascape: lots of holes/ledges; they like to wedge themselves in to sleep
• Flow: moderate; avoid blasting every corner so they have resting spots
• Cover: they can jump when spooked—use a lid or screen top
• Filtration: normal reef filtration; they’re messy once they start eating well

3) What to feed them

They’re famous for eating aiptasia, but your goal is to get them eating “real food” too. Some individuals go straight for frozen, some act like it’s not food for a week, and a few never really figure it out.

In my tanks, small meaty foods work best, offered more often than you’d feed a big predator. Think “little snacks” rather than one huge dump of food.

• Frozen mysis and brine (brine is great as a starter, not a long-term staple)
• Chopped shrimp, clam, scallop (tiny pieces—this fish has a small mouth)
• Blackworms (if you can get them) to kick-start picky eaters
• Quality pellets once they recognize them (soak first if they spit them)
• Live pods help in the early days, especially in an established tank

4) Behavior and tankmates

They’ve got that goofy filefish wobble, and they like to hover, tilt, and poke around. Once they settle in, they usually get pretty personable and will follow you for food.

Temperament-wise, they’re generally peaceful, but they can be pushy with other slow, shy fish. And they’re definitely not built to compete with hyperactive eaters.

• Good tankmates: clownfish, gobies, blennies, cardinals, smaller wrasses that aren’t bullies
• Use caution: tangs and aggressive wrasses that outcompete them at feeding time
• Avoid: fin-nippers and fish that harass slow movers (some damsels, dottybacks, bigger triggers)
• Inverts: usually fine with cleaner shrimp/snails, but keep an eye on tiny ornamental shrimp
• Reef notes: many are “reef-ish,” but some pick at zoas, LPS flesh, or SPS polyps—individuals vary a lot

5) Breeding tips (if you want to try it)

They can spawn in captivity, and it’s pretty cool to see. A bonded pair will often hang together and get more territorial around a chosen area of rock or a flat surface. The male can get protective.

Raising the babies is the hard part. The larvae are tiny and need live planktonic foods, so this is one of those “fun project if you already culture rotifers/pods” situations.

• Pairing: easiest if you start with two juveniles and let them sort it out (watch for bullying)
• Spawning sites: flat rock, small tile, or a smooth patch they can clean
• Feeding breeders: frequent small meaty meals to keep condition up
• Larval rearing: rotifers/pods and a dedicated setup—don’t expect the display tank to raise them

6) Common problems to watch for

The two big issues I see are (1) getting a new one to eat reliably, and (2) unexpected “reef tasting.” Most headaches with this fish trace back to one of those.

• Not eating after purchase: stress, competition, or the fish only recognizes live/aiptasia as food
• Getting outcompeted: they’re slow and can starve in a tank full of speedy eaters
• Coral nipping: zoas, euphyllia, acans, and SPS polyps are common targets if they develop a taste
• Skin/parasite issues from shipping: watch for scratching, rapid breathing, frayed fins
• Jumping: especially in the first week or two