Matted Filefish
Acreichthys tomentosus
The bristletail filefish uses rough, scale-less skin and camouflage to blend into Indo-West Pacific seagrass beds. It employs a strong dorsal spine for defense mechanisms.
Water Temperature
24 - 27 °C
pH Value
8.1 - 8.4
Water type
Marine
Tank level
Bottom and middle
Adult size
12 cm
Minimum tank volume
>= 120 L
Minimum group
>= 1
GH
15 - 25 dGH
KH
8 - 12 dKH
Species description
Geographical Origin and Habitat: This species is native to the Indo-West Pacific, ranging from Indonesia and the Philippines to northern Australia and the Solomon Islands. It primarily inhabits seagrass beds of Zostera, shallow coastal lagoons, and muddy reef flats at depths between 2 and 15 meters, where it blends with algae.
Taxonomy and Morphology: Belongs to the family Monacanthidae, genus Acreichthys. It features a highly laterally compressed body with rough skin lacking traditional scales, covered in tiny bristly spinules. It possesses a strong, lockable first dorsal spine used for defense against predators. It reaches a length of 8-10 cm (3-4 inches).
Social Behavior: A slow-moving, peaceful, and shy fish. It has solitary habits or lives in stable pairs. It relies on its remarkable camouflage to hide from predators and sneak up on small prey. It is peaceful toward other fish species, but adult males may fight if housed together.
Coloration and Sexual Dimorphism: Coloration is highly variable and mottled, changing rapidly to match its surroundings with shades of green, brown, gray, and white. Sexual dimorphism is visible in mature specimens: males possess a well-developed patch of short bristles or spines on each side of the caudal peduncle, which is absent or reduced in females.
Care, breeding and tankmates
Aquarium Setup: Needs an aquarium of at least 150 liters (40 gallons) with plenty of live rock, macroalgae (such as Caulerpa), and quiet areas. Filtration should provide moderate current as it is not a strong swimmer and prefers calm water. A mature tank with a refugium to produce small benthic copepods is ideal.
Diet and Feeding: An opportunistic omnivore. In the aquarium, it is famous for feeding on nuisance Aiptasia and Majano anemones, though individual appetite varies. It must be fed a balanced diet of fine frozen foods (mysis, brine shrimp, chopped krill, clam) and vegetable preparations with spirulina or algae.
Water Quality: Requires stable tropical marine conditions: temperature between 24°C and 28°C (75°F - 82°F), pH 8.1-8.4, salinity/specific gravity of 1.022-1.025, and carbonate hardness (dKH) between 8 and 12. Keep nitrogenous wastes low with regular 10-15% bi-weekly water changes.
Compatibility and Cohabitation: Cohabits peacefully with calm reef fish of similar or larger size. Warning: it is not considered 100% reef-safe. While it eats Aiptasia, if hungry it may nip at soft coral polyps, LPS corals (especially zoanthids), and clam mantles, causing severe damage.
Aquarium Breeding: Captive breeding is possible and has been achieved. They form stable pairs that deposit adhesive eggs on substrate or macroalgae. The male guards the nest until hatching, which takes 4-5 days. Raising larvae requires separate tanks with live rotifers and phytoplankton.
Risks and Diseases: Relatively hardy once acclimated. Can be susceptible to marine parasites (Cryptocaryon, Oodinium) if stressed or exposed to sudden temperature changes. Ensure it feeds regularly during the first weeks of introduction, supplementing food with vitamins.
Geographic Origin and Distribution
This species is native to the Indo-West Pacific, ranging from Indonesia and the Philippines to northern Australia and the Solomon Islands. It primarily inhabits seagrass beds of Zostera, shallow coastal lagoons, and muddy reef flats at depths between 2 and 15 meters, where it blends with algae.
Origin
Tropical oceans and reefsSouth and Southeast AsiaEast AsiaAustralia, New Guinea, and Oceania
Fish profile
- Temperament
- Aggressive
- This filefish is generally peaceful, shy, and slow-moving, making it a gentle addition to a community marine aquarium. They do not pose a threat to most other fish, but they can display territorial behavior towards members of their own species. Because they are passive, they can easily be intimidated or outcompeted by active or aggressive tankmates. They spend much of their time camouflage-mimicking their surroundings, blending into seagrass or rockwork.
- Diet
- Omnivore
- Acreichthys tomentosus is an omnivore widely recognized for its ability to consume pest anemones like Aiptasia and Majano. In addition to these pests, their diet should include a variety of frozen foods such as mysis, brine shrimp, and finely chopped seafood. They also graze on algae, detritus, and small benthic invertebrates from the live rock. Care must be taken as they may occasionally nip at soft and LPS corals, making them reef-safe with caution.
- Life expectancy
- 3-7 years
- In captivity under optimal care, the typical lifespan of the bristle-tail filefish is between 3 and 7 years. Longevity is highly dependent on a stable aquatic environment and a balanced, high-quality diet. Poor water conditions, chronic stress, or nutritional deficiencies can significantly shorten their life expectancy. Providing a stress-free environment with compatible tankmates will help maximize their lifespan.
- Adult size
- 12 cm
- The catalog's scalar value is 12 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 14 cm for this species, recorded as standard length (SL). The taxonomic record consulted is Acreichthys tomentosus (v25.04); male or unsexed record. These figures are not interchangeable: the first is the profile's editorial reference, whereas the second is a published maximum under a specific measurement convention; differences among sources can reflect sex, population, life stage and measuring method.
- Sex ratio
- 1:1 ratio
- These filefish are typically kept singly or in mated pairs (1:1 ratio) to prevent territorial aggression. Males can be highly aggressive towards other males, so stocking multiple individuals of the same sex in a single tank is not recommended. In very large systems with abundant hiding spots, a small group can sometimes be housed if introduced simultaneously. A mated pair is the safest option for keeping more than one specimen together.
- Feeding frequency
- Twice daily
- In a home aquarium, they should be fed small portions two to three times daily. Because they are continuous grazers with small digestive tracts, frequent feedings are necessary to maintain their health and weight. In tanks with a rich population of copepods or pest anemones, they will forage throughout the day, reducing the need for intensive feeding. However, supplemental feedings are still required to ensure they receive a balanced diet.
- Bioload
- Low to Medium
- Acreichthys tomentosus has a relatively low to moderate biological load due to its small size and slow-moving nature. It does not produce a significant amount of waste compared to larger or more active marine species. However, a well-established filtration system with an efficient protein skimmer is still essential to maintain pristine water quality. Regular water changes and monitoring of nitrate levels are highly recommended to ensure a stable environment.
- Flow
- Strong
- This species prefers weak to moderate water flow within the aquarium. They are weak and clumsy swimmers, using their dorsal and anal fins for precise maneuvering rather than speed. Strong, laminar currents can exhaust the fish and make it difficult for them to feed or hover comfortably. Designing the aquascape to include low-flow zones and calm areas is crucial for their well-being.
- Jump risk
- Yes
- Although Acreichthys tomentosus is not known as an active jumper like wrasses, it can jump when startled or stressed. To prevent accidental escapes, a tight-fitting lid or a secure mesh cover is highly recommended. This is particularly important during the acclimatization phase when the fish is adapting to its new environment. Ensuring that any small gaps around filters or cords are sealed will minimize the risk of jumping.
- Reproduction
- Oviparous
- Breeding in captivity has been achieved but is considered difficult for amateur hobbyists. These filefish are demersal spawners, with females laying sticky eggs on substrates like algae or live rock, which the male then fertilizes and guards. Raising the tiny fry is exceptionally challenging due to the lack of a traditional pelagic larval phase and their need for specialized live micro-foods. While spawning behavior is common in established pairs, successfully rearing the offspring requires dedicated breeding setups.
- Compatibility & tankmates
- Not reef safe
- Acreichthys tomentosus is compatible with a wide range of peaceful marine fish such as gobies, cardinalfish, and clownfish. They should not be housed with aggressive, fast-swimming species that might outcompete them for food or bully them. Furthermore, they are only semi-compatible with reef aquariums, as they may nip at polyps, zoanthids, and ornamental shrimp. Keeping them with aggressive invertebrates or predatory fish should be avoided entirely.
- Tank level
- Middle/Bottom
- This species primarily occupies the bottom and middle zones of the aquarium, where it spends its time hovering near live rock or artificial decor. They are demersal fish that feel most secure when they are close to structure and shelter. They rarely swim in the open, upper water column unless they are feeding or searching for food. Providing plenty of rockwork and caves will help them feel comfortable in their preferred swimming zone.
Scientific Parameters & Models
FishBase
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 3 ± 0.39 se
- Resilience
- High (less than 15 months)
- Generation time
- 1.3 years
- Phylogenetic uniqueness (PD50)
- 0.625
- Bayesian Length-Weight
- a = 0.0257, b = 2.97
- VulnerabilityLow vulnerability (16 / 100)
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
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