What Divers Should Know About Filefish

Filefish (Monacanthidae) are a diverse family found across the tropical to subtropical zones of the Atlantic, Pacific, and Indian Oceans. These distinctive marine fish, sometimes known as foolfish or leatherjackets, derive their common name from their rough, sandpapery skin and laterally compressed, rhomboid-shaped bodies. Many species display elaborate cryptic patterns, often bearing a visual resemblance to their close relatives, the triggerfish. Deeply keeled bodies are also notable, giving a false impression of size when viewed from the flank.

Crowned with a slender, retractable spine that can be locked erect, filefish utilize this feature, along with an articulated pelvic bone creating a movable "dewlap," as a defensive strategy. This simultaneous erection can make them appear larger or more challenging for predators to remove from a confined space. Though the impressive scrawled filefish (Aluterus scriptus) is known to reach up to 110 cm (43 in) in length, most species typically measure less than 60 cm (24 in). Some species also exhibit marked sexual dimorphism, with males and females differing in coloration and body shape.