What is a saltwater filefish?
Filefish are a group of laterally flattened, slow-moving marine fish related to triggerfish and pufferfish. The name comes from their rough, file-like skin. They typically swim with small, rippling fin movements and are known for camouflage: many species mimic seaweed, coral or floating debris.
Only a few filefish are regularly kept in home aquariums, and some are considerably harder to keep than others. The one most hobbyists meet first is the Aiptasia-eating filefish.
The Aiptasia-eating filefish
The Aiptasia-eating filefish (Acreichthys tomentosus, also sold as the bristle-tailed filefish) is the species most often recommended for reef tanks. Common care-sheet details:
- Adult size: roughly 3 to 4 inches, with some sources listing slightly larger
- Temperament: generally peaceful and a bit shy
- Appearance: mottled green, tan and brown with small skin flaps that help it blend in
- Minimum tank size: often given as 30 gallons
The fish is sold mainly because it may eat Aiptasia, a pest anemone that spreads across reef rockwork. Results vary a lot between individuals. Some filefish eat Aiptasia eagerly, others ignore it completely. Treat it as a possible help, not a guaranteed fix.
Tank setup and water parameters
Filefish are commonly kept in typical reef conditions:
- Temperature about 72 to 78 degrees Fahrenheit
- Specific gravity about 1.020 to 1.025
- pH about 8.1 to 8.4
Use a mature, stable system with live rock for grazing and hiding. A secure lid is wise, since many marine fish can jump if startled. Gentle flow and a few shaded spots help a shy fish settle in.
Feeding
Filefish are generally described as omnivores. A varied diet might include:
- Aiptasia, where available
- Frozen mysis and brine shrimp
- Chopped seafood such as squid or clam
- Marine pellets or flakes once the fish accepts them
A common problem is starvation after the pest anemones are gone. A filefish that was bought to eat Aiptasia still needs regular feeding. Offer small amounts daily and watch for a sunken belly. Because these fish are slow, make sure faster tank mates are not taking all the food.
Reef compatibility and tank mates
Retailers often label the Aiptasia-eating filefish as reef-safe with caution. Some individuals nip at soft corals, zoanthids, polyps, feather dusters or small stony coral polyps. Introduce it carefully and be ready to remove it if corals are damaged.
Good tank mates are typically peaceful and similarly sized. Avoid aggressive fish such as larger triggerfish, bullying wrasses or territorial damsels that may stress a shy filefish. Compare this with the more territorial flame hawkfish, which is bolder and not an ideal companion for a timid fish in a small tank.
Other filefish species
Other filefish appear occasionally in the trade, and their needs differ:
- Harlequin or orangespotted filefish are associated with feeding on live coral polyps in the wild and are generally considered very difficult to keep without a specialized diet.
- Scrawled filefish and other larger species can grow well beyond the sizes above and need much bigger tanks.
- Some filefish are sold as algae or pest eaters, but their diet may not match what a home tank provides.
Research the specific species and ask your retailer what the fish is currently eating before buying.
What else eats Aiptasia?
If a filefish is not the right choice, hobbyists commonly use other approaches:
- Peppermint shrimp (Lysmata species), which many keepers report eating Aiptasia, though results vary
- Berghia nudibranchs, a specialist predator that eats little else, so they need an Aiptasia supply
- Direct treatments such as injecting the anemone or using kalkwasser paste, and manual removal
- Some butterflyfish, which are risky because they can also eat desirable corals
Whatever you choose, address the cause too. Aiptasia tends to flourish in tanks with excess nutrients.
Is filefish good to eat?
Some filefish are eaten as food in parts of the world. However, aquarium fish are not raised or handled for eating, and certain reef fish can carry toxins. This is a safety question for local fisheries and food authorities, so do not assume a fish you can buy for a tank is safe to eat.
Related reading
For more ideas on unusual reef fish, see our list of cool saltwater fish to own.