Bristletail Filefish (Aiptasia-Eating Filefish)
Acreichthys tomentosus
The Bristletail Filefish features a rugged, elongated body covered in small, spiny scales, with a mottled coloration of brown and green.
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About the Bristletail Filefish (Aiptasia-Eating Filefish)
This little weirdo is one of my favorites because it's got that goofy filefish "face," a knack for wedging itself into rockwork, and a ton of personality once it settles in. People love them for the chance they'll snack on nuisance Aiptasia, but even when they're not on pest patrol they're just fun to watch cruise around and pick at stuff all day.
Quick Facts
Size
12 cm
Temperament
Peaceful
Difficulty
Intermediate
Min Tank Size
30 gallons
Lifespan
3-7 years
Origin
Indo-West Pacific (East Africa/Red Sea to the western/central Pacific; north to Japan/Ryukyu; south to Australia; east to Fiji/Tonga)
Diet
Omnivore - varied frozen foods (mysis/brine/chopped seafood) plus some algae/nori and quality pellets; may eat Aiptasia but still requires prepared foods
Water Parameters
22.2-27.2°C
8.1-8.4
8-12 dGH
Need a heater for this species?
This species needs 22.2-27.2°C in a 30 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Give them a mature tank with lots of rockwork and nooks-when they're stressed they wedge themselves into tight spots and "play dead," so don't panic if you don't see it for a while.
- Keep salinity stable around 1.020-1.026 (many sources list ~1.020-1.025) and temp ~22-27°C (72-81°F); avoid big swings, especially right after shipping/acclimation.
- They're great at mowing Aiptasia, but once the Aiptasia is gone you've still got to feed-train onto frozen mysis, brine, chopped shrimp/clam, and small pellets by offering food right in front of their face with tongs.
- Feed small amounts 2-3x a day at first; they can be slow, picky eaters and will lose weight fast if faster fish outcompete them.
- Reef-safe-ish: many ignore corals, but some will pick at zoas, LPS, and even clam mantles-watch for "mystery nips" after lights out and be ready with a backup plan.
- Avoid housing with aggressive wrasses, dottybacks, triggers, or anything that will harass them or steal food; they do best with chill community fish and not-too-pushy tangs.
- If possible, quarantine them when you get them—they often arrive thin or shy and can benefit from careful observation and feeding support. Keep an eye out for common marine parasites like ich and velvet, and avoid stressing them during acclimation.
Compatibility
Good Tankmates
- Chill reef fish like ocellaris/percula clownfish - they usually ignore the filefish, and the filefish just cruises around doing its weird leaf-fish thing
- Smaller, peaceful wrasses (think flasher/fairy wrasses) - active but not bully-types, and they don't tend to hassle a filefish
- Gobies and blennies that mind their own business (watchman goby, tailspot blenny, etc.) - great because they occupy different zones and aren't pushy
- Cardinals and chromis - mellow midwater fish that won't compete too hard at feeding time if you're on top of target-feeding the filefish
- Tangs that aren't jerks (kole/tomini in a properly sized tank) - generally fine as long as the tang isn't an established territory-hog
- Dwarf angelfish (with caution) - monitor closely for bullying and coral/invert nipping by either species
- Compatible with caution: Lions/Scorpions - predation risk depends on size; do not mix if the predator can swallow the filefish
Avoid
- Triggerfish (most of them) - too pushy, too bitey, and a filefish is not built for that kind of neighborhood drama
- Large aggressive wrasses (like many Thalassoma) - they'll outcompete the filefish for food and may harass it nonstop
- Dottybacks and mean damsels - classic fin-nippers/territorial punks, and the filefish tends to be slow and easily stressed
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.
Most people buy them for aiptasia control. They can be amazing… but they’re not a guaranteed “set it and forget it” solution.
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
If you can, quarantine them. They ship a bit beat-up sometimes, and getting them eating confidently in a quiet QT can save you a lot of frustration later.
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
If yours won’t touch frozen, try a small chunk of clam on the half shell wedged into the rock. The scent pulls them in, and the picking behavior is natural for them.
Don’t buy one assuming it’ll only eat aiptasia and be done. Aiptasia can run out, and a hungry filefish may start “sampling” corals or polyps.
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
Coral picking is a real thing with this species. Plenty behave, plenty don’t. If your reef is packed with expensive LPS/zoas, have a backup plan (fish trap, acclimation box, or a willing friend).
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
If you just want aiptasia control, breeding is optional rabbit-hole territory. But if you like fish behavior, watching a pair set up a spawning area is genuinely neat.
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
Feed with intention: use a turkey baster or feeding tube to deliver food right near the filefish at first. Once it learns “food shows up here,” life gets a lot easier.
If you rely on it for aiptasia control and then it stops eating them, don’t panic-buy a second one. Figure out if the first fish is well-fed, getting bullied, or has already knocked the aiptasia back and moved on to easier targets.
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