Acreichthys tomentosus – Bristle-Tail File-Fish

Acreichthys tomentosus or Bristle-tail Filevis is sometimes used to control Aiptasia. However, they are not always reef safe!

Acreichthys tomentosus – Bristle-Tail File-Fish

Acreichthys tomentosus was first described by Linnaeus in 1758. They are part of the family Monacanthidae or the File-fish. They have several common names: Bristle-Tail File-Fish, Banded Leatherjacket, Seagrass Filefish.


The color of Acreichthys tomentosus is difficult to describe. They are spotted but the color is adapted by fish to the environment. They can change the color and pattern of the spots at lightning speed. As a result, they are well camouflaged and do not stand out against the background. They can reach a maximum total length of about 16 centimeters but often remain smaller.

The difference between the male and female can only be seen when they are adults. The males develop a kind of brush-like projections near the tail. In English they are therefore also called Bristle-tail Filefish. The males are also slightly larger than the females.

On their head they have a strong spine that clearly stands out. Be careful not to damage it when catching and transporting the Seagrass Filefish. Also make sure that this spine does not puncture the bag in which you transport them. It may even be better to use two bags to avoid accidents.


Adult Bristle-Tail File-Fish inhabit the reefs, weeds and debris areas of the reefs. They are also often seen in seagrass, hence the common name Seagrass Filevis.

They occur in the Indian Ocean and western Pacific Ocean, from East Africa north to the Ryukyu Islands, south to Australia. They are usually found in shallow water from 2 to 15 meters deep.


In the wild, they mainly feed on bristle worms, amphipods (Amphipoda) and invertebrates. Aiptasia are also on their menu.

They are therefore also used in the aquarium to combat Aiptasia. You have to be a bit lucky with that. Some Bristle-Tail File-Fish leave the other corals alone and eat the food you offer, others do sip from the corals. Buttons in particular are sometimes not left alone.

Of the Filefish, the Bristle-Tail File-Fish is the one that behaves best. As long as you feed them enough to stay away from the corals, they will often be fine. Just don’t feed them so much that they are no longer hungry, then they won’t eat the Aiptasia…’s a bit of a search for a good balance.

You can feed them in the aquarium with Aiptasia, Artemia, Frozen foods, Worms, algae etc. Preferably feed them in small amounts, several times a day.

The aquarium

You can keep a couple of Acreichthys tomentosus in an aquarium from about 400 liters. To graze they need enough living rock and coral sand. Only place them in a well-established aquarium to prevent that there is not enough grazing.

In general, this is a calm, peace-loving species. Only adult males can react somewhat aggressively to each other. Do not combine them with overly large or aggressive species. They wither away if they are constantly harassed or if the brush-shaped appendages of the growing males are constantly snapped.

As mentioned, they are not always reef safe. Most specimens like to eat Aiptasia, some don’t care at all. Some of the Bristle-Tail File-Fish are reef safe but some are nipping at corals, especially zoanthids and palythoas. They also sometimes want to grab a shrimp or snail.

Breeding Acreichthys tomentosus

It is quite possible to breed the Seagrass Filefish in the aquarium. To do this, simply place a male and female in the aquarium.

The sticky eggs are laid in a sheltered spot on the substrate. A nest usually consists of around 300 eggs. The nest is protected until the eggs hatch. That is usually three to four days later. You can feed the newly hatched fish with rotifers and freshly hatched brine shrimp.



John de Lange

Copyright images 

John de Lange
Klaus Stiefel
Steve Childs – CC BY 2.0



Last Updated on 31 July 2021 by John

Additional information





Common names

Banded Leatherjacket, Bristle-Tail File-Fish, Seagrass Filefish


Social Behaviour

Breeding behaviour




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