Fish Identification Photos: Unicorn Filefish, Unicorn Leatherjacket, Aluterus monoceros: The Unicorn Filefish is characterized by several unique features including a convex upper snout and a concave lower snout. The Unicorn Filefish is tan in color with a few brown blotches and spots on its upper sides. It has a straight caudal fin. The Unicorn Filefish can be confused with the Scrawled Filefish, Aluterus scriptus. However, in the Scrawled Filefish both the upper and lower snouts are concave, and it also has broken blue lines and small black dots on it sides, and a pointed dorsal fin.

The Unicorn Filefish is a member of a group of filefishes comprising the Monacanthidae Family. The Filefish are rather bizarre looking fish, belonging to a highly specialized order noted for unique defensive adaptations. Filefish normally have two dorsal spines with a unique ability to lock the first dorsal in an erect position that is released by a trigger mechanism generated by the second. This allows them to wedge themselves into rock crevices making it very difficult for a predator to get them out.

They have human-like teeth which are truly lethal because they eat coral and rocks day in and day out. Their skin is covered with small, rough textured scales that feel velvety to the touch. They are fearless carnivores feeding on sea urchins, small crustaceans, and mollusks. Globally there have been 95 species of Monacanthidae identified of which only two are found in the Sea of Cortez.

The Unicorn Filefish is normally found in rocky structure in the first 100 feet of the water column. It reaches a maximum length of 30 inches.

In Mexico, the Unicorn Filefish has been reported from Magdalena Bay to Cabo San Lucas on the Pacific side of the Baja California peninsula, from Mazatlan south to Guatemala on the mainland, and around all oceanic islands.

Note: the two filefish previously recorded in the Sea of Cortez are the Scrawled Filefish, Aluterus scriptus, and the Barred Filefish, Cantherines dumerilii. The collection (at 27 degrees N and 112 degrees W) reported below by Mike Kanzler is the first known documentation of a third filefish living in the Sea of Cortez.

Unicorn Filefish, Unicorn Leatherjacket, Aluterus monoceros: Donated to MexFish.com by the Mexican commercial fishermen of Todos Santos, Baja California Sur, April 2009. Size 20 inches. Photo courtesy of John Snow. Unicorn Filefish, Unicorn Leatherjacket, Aluterus monoceros: Caught from shore during the last hours of daylight in 76 to 77-degree water, June 10, 2004, in rocky structure, on cut squid, at a water depth of 12-15 feet, on a small, rocky point, the shore of Isla San Marcos, near Santa Rosalia, Baja California Sur, Mexico, about one-half mile from town. Two identical fish were taken on the same trip. Catch by residents of the island. Description and photo courtesy of Mike Kanzler. Fish identification John Snow, confirmed by Ross Robertson, Smithsonian Institute, Panama.   Unicorn Filefish, Unicorn Leatherjacket, Aluterus monoceros: Caught by angler Wayne Diedre of Modesto, Calif., while fishing on a panga with La Paz' Tailhunter international. PHOTO COURTESY OF JONATHAN ROLDAN.