Drifting around in the large marine tank at Bristol Zoo Aquarium are some small fish that get easily overlooked. This is of course part of their plan – the Tomentose Filefish Acreicthys tomentosus is a master of disguise.Belonging to the same order Tetraodontiformes as last weeks’ Porcupine Fish, it is in a separate family Monacanthidae, which is most closely related to the Trigger fishes Balistidae, and like other members of the order its strategy for survival involves appearing unlike anything a predator would want to eat. Some species of filefish get over 1m, but the Tomentose only grows to a maximum of 12cm, usually less. The larger species may be important food fish – the annual catch of Cantherines spp has been around 200,000 tonnes, but whether this is sustainable or not I am not sure. Overfishing is a worldwide problem, as I am sure readers of this blog are well aware.
Unlike triggerfish, which tend to specialise in hard-shelled prey like crabs and shellfish, filefish tend to focus on smaller and softer bodied prey, with some being partly on entirely vegetarian, and a few specialising in coral polyps. Tomentose filefish have a varied diet, but will prey on some coelenterates as well as small crustaceans – they are sometimes sold as Aiptasia-eating Filefish owing to their fondness for Aiptasia anemones which are a common pest in marine aquaria.
Tomentose filefish rely mainly on camouflage to avoid being eaten by predators. They seem to drift in the current as they examine the substrate for anything to eat. To assist in the disguise, they can also change colour and pattern. They need to be well disguised – at their size they often fall prey to larger reef predators. They get their name from the bristly projections (tomentose means wolly) along their sides, especially in males.
Tomentose filefish are substrate spawners. A nest, containing around 300 1mm sized eggs is laid and guarded by the female in a patch of algae. After 3 days they hatch into 2.7mm larvae which drift in the plankton, beginning to feed at 36 hours post hatching. By 15 days they are small juvenile fish. In the wild they and many other filefish species are associated with floating mats of Sargassum weed, where their camouflage is highly effective. In the related species Acreicthys radiatus juveniles have been seen to anchor themselves at night by biting into algae.
As with many marine fish, in recent years captive breeding has been successfully achieved with this species, with the first record in 2008. Today at least 3 species of filefish are being commercially produced for the aquarium trade and it is a realistic species to be bred by a home aquarist. They do not appear to be especially territorial, and larvae have been raised on rotifers and harpactid copepods. For a Youtube clip of a nest and newly hatched larvae see here: Https://www.youtube.com/watch?v=7sNI2fAkS4E
Cover image from Wikipedia