File Fish

There are about 107 different species of File Fish which are also known as foolfish, leatherjackets or shingles and they are generally found in the Atlantic, Pacific and Indian Oceans. The File Fish family is closely related to the Trigger Fish, Puffer Fish and Trunk Fish.
File Fish are oddly-shaped fish often with dazzlingly cryptic patterns. Many species change in shape with age and the juveniles tend to be circular and very compressed whereas the adults are more elongated. They have soft, simple fins with comparatively small pectoral fins and truncated fan-shaped tail fins; a slender, retractable spine crowns the head. Although there are usually two of these spines, the second spine is greatly reduced, being used only to lock the first spine in the erect position. They also fan out the fin on their belly when they are frightened and want to alarm a possible predator. Filefish alter their colour and pattern to match their surrounds in order to deter such predators...
The filefish has tiny prickly scales that in some species cannot be seen by the naked eye. It is their laterally compressed bodies and rough, sandpapery skin that inspired the filefish's common name; it is said that dried filefish skin was once used to finish wooden boats and that fisherman used to light matches with their skin because it is so coarse.
Here on Koh Tao we regularly see the Scrawled Filefish - Aluterus scriptus, the Bearded Filefish - Anacanthus barbatus and the the Strap-Weed Filefish - Pseudomonacanthus macrurus.  We also have had rare sightings of the Leafy Filefish - Chaetodermis pencilligerus and the Fan-bellied filefish- monacanthus chinensis......


The Scrawled Filefish - Aluterus scriptus also known as the Scribbled filefish and is the largest of the filefish family, being able to grow up to 110 cm in length! – This is our most commonly seen filefish, although most ones we see are below 60 cm in length.  They have an olive-brown to pale grey body with irregular blue lines and black dots all over their surface. The Scrawled filefish has two switchblades on each side of its tail and if a predator threatens they will lash out to counterattack. While the scrawled filefish is a slow swimmer, the broom-like tail provides thrust for short burst of speed to make a quick dash for safety inside the reef and when pursued they sometimes make grunting sounds. The eyes of this wary fish are set high on its head and can move independently so that it can scan the reef for food and predators If you see one of these beautiful fish caught in the light it looks like they are shimmering and they make a beautiful photograph......


The Bearded Filefish - Anacanthus barbatus - this is a very strange looking file fish with its elongated shape, longitudinal brown stripes and an articulated barbel on the chin. At a first sight in fact it could be mistaken as a pipe fish or a ghost pipe fish but if observed carefully you can see the moving dorsal and anal fins, also the back spine and the ventral fins that can be opened like a fan. It is normally seen hanging around the buoy lines at various dive sites and can grow up to 35cm long.


The Strap-weed filefish - Pseudomonacanthus macrurus is also called the Smallspotted leatherjacket and can grow up to 45cm long. It has a highly variable pattern that is generally yellowish background with white markings. There are white patches from nose to a little past the dorsal spine and a white stripe along the centre of the body from the gill opening. Tiny filaments sparsely cover the body but there are no bristles on the tail. This filefish is normally seen at Junkyard dive site and looks pretty impressive...


The Leafy file fish - Chaetodermis pencilligerus, also referred to as the Tassle Filefish can grow up to 30cm. It is an interesting and unique relative of the species and has been seen here at Pottery Pinnacles. The Tassle Filefish gets its name from the multiple, tiny tassle-like protuberances over its entire body; which in conjunction with their broken, horizontal striping, they have an efficient natural camouflage and can blend into the surrounding marine algae among the reef of their natural habitat while they search for food or hide from danger.


Fan bellied filefish Monacanthus chinensis - has been sighted at South West Pinnacle.... The Fan-bellied Leatherjacket or Fan-bellied Filefish has a flattened body and trigger-like dorsal spine that is common with all filefish. It also has a large, flat fan-like fin on its underside. Its body is a variable greenish-brown and may have darker spots or wide, diagonal bands. It can grow up to 38cm though most sightings have been a lot smaller.
Just like their relatives the Triggerfish, filefish use their spines for safety. When threatened they will dive into a hole or crevice in the reef and wedge themselves into the shelter by erecting the large dorsal spine on their head, which is then locked into place by the second spine. At the same time their belly spine extends so that they are wedged in securely. In case of an emergency, the powerful jaws grasp the wall of the hole providing additional security. Filefish also use this wedging behaviour at night when they rest within the reef.