The glass anemone destroyer - the bristle-tail filefish (Acreichthys tomentosus)
A number of years ago, I shared information about the bristle-tail filefish (Acreichthys tomentosus) in a magazine article. I found that in Europe, that many aquarists included this species in their reef aquarium fish community to take care of both glass anemones (Aiptasia spp.) and the dreaded Majano anemones (Anemonia cf. majano). The European reef-keepers swore up and down that they did not harm other cnidarians in the tank. When originally introducing A. tomentosus as a potential reef aquarium inhabitant I did suggest that there was some data that they may pick at xeniid corals, leather corals and large-polyped stony corals. Since that time, I have kept a dozen of these fish in my own and customer aquariums and have found that they are not as trust-worthy as I had hoped. Yes, they love to munch on those annoying little anemones (at least some individuals anyway), but they also might nip at the tentacles of more desirable sea anemones (e.g., Entacmaea quadricolor), the tips of gorgonian branches and the fleshy polyps of a variety of large-polyped stony corals (e.g., Acanthastrea, Turbinaria, Lobophyllia, Trachyphyllia).
Is there a place for these filefish in the reef aquarium? Most definitely - they are still one of the best biological control I have found for clearing a tank of Aiptasia or Majano anemones. To give you an example: I had customer’s aquarium that had been overtaken by glass anemones (some of the largest Aptasia I have ever seen). I added two A. tomentosus and within a month the number of Aptasia had greatly declined. After several months, there was not an Aiptasia to be found. I had tried peppermint shrimp in this tank and Aeolidella stephanieae - the so called Berghia sea slugs. These anemone-eating inverts did little good in this anemone-infested aquarium, unlike our friend A. tomentosus. (That is not to say that some aquarists have not had luck getting these invertebrates to “take out” their anemone enemies, but they are less consistent in bringing Aiptasia, both large and small, under control like the bristle-tail filefish.) I also want to reiterate that the fringe-tail filefish is the best biological control of Manjano sea anemones that I know of.
Like other fishes (including those utilized to deal with pests in the reef aquarium), there can be individual variation in their desire to eat the anemone's you want to get rid of. I have seen individuals that would not touch an Aiptasia. However, in my experience, a greater percentage will dine on these anemones than the other common natural Aiptasia-eliminator, the copperbanded butterflyfish (more on this beastie below).
The idea situation may be to remove the bristle-tail filefish once it has the pestilent sea anemones in check. Of course, this can be easier said than done! They are not that easy to catch with a fish trap (although some individuals may enter if you add a tasty treat, like a piece of table shrimp or scallop), and trying to round up on these secretive little guys in a tank full of live rock can be a real trick. The bottom line: adding a filefish to your reef tank is always a calculated risk.
One thing to be aware of is that not all "Aiptasia-eating" filefish sold in the market are A. tomentosus. For example, I have seen the Atlantic species, Monacanthus ciliatus, sold as anemone-eating filefish. While my experience with this species is limited, I don't believe it to be as effective at Aiptasia extermination.
This butterflyfish hates glass anemones! Well, most of the time they will eat them
in your reef tank.
Regarding the copperbanded butterflyfish (Chelmon rostratus) – they can sometimes be very effective at helping deal with Aiptasia outbreaks. Most individuals (and other members of the genus Chelmon) can be kept in a reef tank with most soft corals and small-polyped stony corals, although some individuals may nip at large-polyped stony corals, certain soft corals (including xeniids and clavulariids), and zoanthids. Christmas tree worms are also a potential target of C. rostratus.
Another downside with C. rostratus is that it can be quite delicate. Your chances of success will greatly increase if you’re selective about the specimen you add to your tank. Avoid emaciated individuals unless you hope to try and rescue the fish. Unfortunately, thin individuals are not likely to recover. Some aquarists have suggested that smaller individuals (around 3-inches in length) fare better in captivity than adults. The idea is that smaller individuals are more likely to acclimate to a new food source than an older conspecific (the old, “You can’t teach an old dog new tricks.” phenomenon!). That said, you should be aware that the metabolic needs of a juvenile fish will be higher than that of an adult. As a result, you will need to make sure you feed a young fish frequently or ensure there is an adequate natural food source present in the aquarium.
The copperbanded butterflyfish are thought to feed heavily on tubeworm feeding appendages and small crustaceans in the wild. A tank with live rock will provide some normal fodder. This will provide a hungry copperbanded with nutritional snacks between meals. Natural prey items are also important if a newly added C. rostratus is reluctant to eat aquarium foods when first introduced to the aquarium.
Remember, adding Aiptasia eating fish to an aquarium containing corals is always a calculated risk. But, it is a risk many aquarist find worth of taking if stricken by an anemone plague!
© Scott W. Michael - article and photos should not be reproduced without the authors permission