Monacanthidae
The filefish, also known as foolfish, leatherjackets, or shingles, belongs to the Monacanthidae family. These diverse marine fish are found in tropical to subtropical regions of the Atlantic, Pacific, and 🌊 Indian Oceans. With approximately 102 species in 27 genera, filefish are closely related to triggerfish, pufferfish, and trunkfish (boxfish).
More than half of the species can be found in 🇦🇺 Australian waters, with 58 species in 23 genera. The filefish gets its name from its laterally compressed body and rough, sandpapery skin. In fact, dried filefish skin was historically used to finish wooden boats.
Filefish resemble triggerfish, with their rhomboid shape and intricate cryptic patterns. Their bodies are keeled, giving a misleading impression of size when viewed from the flanks. They have soft, simple fins, small pectoral fins, truncated tail fins, and a retractable spine on their heads. The second spine is typically reduced and only used to secure the first spine in an upright position, hence the name Monacanthidae, derived from the Greek words for "one" and "thorn". Some species also have recurved spines on the base of their tail.
Filefish have specialized incisor teeth in their small terminal mouths. There are four teeth in the inner series and six in the outer series of the upper jaw, while the lower jaw typically has four to six teeth in the outer series. Their snout is tapered and projecting, and their eyes are located high on their heads. The rough scales of filefish overlap and have small spikes, giving them their characteristic file-like appearance. Some species have such small scales that they appear scaleless. Like triggerfish, filefish have small gill openings and elongated pelvic bones that create a "dewlap" of skin, extending between the bone's sharply keeled termination and the belly. This pelvic structure is capable of upward and downward movement, forming a large dewlap to make the fish appear deeper in the body than they actually are. Some filefish can erect their dorsal spine and pelvis simultaneously to make it harder for predators to remove them from caves.
The scrawled filefish (Aluterus scriptus) is the largest species, reaching up to 110 cm (43 in) in length. Most filefish species are less than 60 cm (24 in) long. Some species exhibit sexual dimorphism, with males and females having different coloration, body shapes, and males having larger caudal spines and bristles.
Adult filefish primarily inhabit shallow waters, with depths of no more than 30 meters. They can be found in lagoons, seaward reefs, seagrass beds, and even estuaries. Some species are closely associated with dense sargassum mats, a common seaweed. These filefish, like the planehead filefish (Stephanolepis hispidus), are colored and patterned to blend in with their weedy environments.
Filefish are usually solitary, in pairs, or small groups, depending on the species. Due to their small fins, they are not particularly agile swimmers and have a slow movement. They are often observed drifting head downward among seaweed to deceive both predators and prey. When threatened, filefish may retreat into crevices in the reef.
The feeding habits of filefish vary across species. Some feed exclusively on algae and seagrass, while others also consume small benthic invertebrates such as tunicates, gorgonians, hydrozoans, and even corals. The latter two habits make it challenging to introduce filefish into aquariums.
Filefish spawn at prepared bottom sites that are guarded by males. Depending on the species, both the male and female or just the male will guard the brood. The juvenile filefish are pelagic, meaning they frequent open water. Sargassum provides a safe haven for many species, as both the fish and weed are at the mercy of ocean currents. Juvenile filefish face predation risks from tuna and dolphinfish.
