Unicorn Filefish

The Unicorn Filefish, scientifically known as Aluterus monoceros and also called the Unicorn Leatherjacket Filefish, is a marine species typically found in subtropical regions. Found at depths ranging from 1 to 80 meters (approximately 3 to 262 feet), this fish is often associated with reefs. It can grow up to a maximum length of 76.2 centimeters (about 30 inches), although the common length is around 40 centimeters (16 inches). The heaviest recorded specimen weighs 2.7 kilograms (approximately 6 pounds).

These fish are occasionally observed in shallow waters near steep drop-offs, whether solitary, in pairs, or sometimes in groups of five or six at depths less than 10 meters (about 33 feet). Juvenile Unicorn Filefish live in open water and are often seen near floating objects. While juveniles are rarely seen near reefs, they tend to associate with large jellies which may bring them closer to reefs. Adults may nest on sandflats adjacent to reefs in deeper waters or gather in large schools under weed-rafts that are common during the wet season. Their diet primarily consists of organisms that live on the ocean floor.

In terms of physical characteristics, adult Unicorn Filefish have two dorsal spines and between 45 to 52 dorsal soft rays. They lack anal spines but have between 47 to 53 anal soft rays. Large specimens lose their rudimentary pelvic spine, and their snouts become convex. Their appearance includes a sandy to grey color with small brown spots on the upper body, pale yellowish to brownish soft dorsal and anal fins, and a caudal membrane that is blackish brown.

This species is distributed circumtropically, ranging from the western Atlantic—where they can be found from Massachusetts, USA to Argentina—to the eastern Atlantic along the west coast of tropical Africa. They are also present in the eastern Pacific, from 🇬🇹 Guatemala to possibly 🇲🇽 Mexico and 🇨🇱 Chile. In the undefined, they are found near 🇲🇿 Mozambique and 🇿🇦 South Africa, and they have been recently recorded in Reunion.

The name "Aluterus" comes from the Greek, meaning "not free or detached," and refers to the unique characteristic of their pelvis, which does not project spines as seen in triggerfish.