Moorish Idol, Zanclus cornutus
The Moorish Idol, Zanclus cornutus, whose common Spanish name is ídolo moro, is a member of the Moorish Idol or Zanclidae Family, known as ídolos moros in Mexico. The Moorish Idol is the sole global member of the genus Zanclus and the sole global member of the Zanclidae Family. It is found on a limited basis in Mexican waters of both the Atlantic and the Pacific.
The Moorish Idols have deep, strongly compressed, disc-shaped bodies. Males and females cannot be separated visually. A key to identification is their elongated whip-like dorsal spine, the philomantis extension. They are distinctively colored being white anteriorly and yellow posteriorly and having two broad vertical black bars, the first being wide and covering the head and the second located at the rear of the body and covering the anal and dorsal fins. Their dorsal fin filament is white. Their head has a long protruding tubular snout with short horn-like projections above the eyes. Their eyes are set high on the head and they have a small terminal mouth equipped with long bristle-like teeth. Their snout is black with an orange-bordered saddle and their caudal fin is black with a white margin. Their anal fin is triangular with 3 spines and 31 to 37 rays; their caudal fin is concave; their dorsal fin is sickle-shaped with 6x or seven dramatically elongated spines and 39 to 43 rays; and their pectoral fin has extended rays.
The Moorish Idols are found over hard bottom structures including shallow water reef flats and rocky and coral areas from the surface to depths up to 590 feet. They reach a maximum length of 30 cm (12 inches). They travel in small groups or in large schools of greater than 100 individuals. They have a preference for water temperatures between 25oC (75oF) and 28oC (82oF). They are highly selective omnivores and feed on algae, sponges, and other invertebrates. During the night, they attach themselves to the bottom and change to a drab color. Their long streamer, the philomantis extension, is believed to a deterrent to predators. They are preyed upon by Moray Eels. Reproduction is not well understood but involves the release of pelagic eggs with external fertilization. Males become aggressive while breeding. They have an exceedingly long pelagic larval stage, which contributes to the wide distribution of this species. Larvae become very long and transition rapidly into excellent swimmers that are found on the surface for an extended period of time before transitioning to the reef environment. They have a lifespan of up to four years.
The Moorish Idols are widespread in the Indo-Pacific and tropical Eastern Pacific and are now expanding into other areas, which has been attributed to aquarium releases. In Mexican waters they have a limited distribution and are found along the southeast coast of Baja and from Mazatlán south along the coast of the mainland to Guatemala. The collections photographed below extend the range into the southwest tip of the Baja in the Pacific to at least 40 miles north.
The Moorish Idol is similar in appearance to several of the butterflyfish, including the Scythe Butterflyfish, Prognathodes falcifer, however, the butterflyfish lack the triangular anal fin and the philomantis extension of the dorsal fin.
The Moorish Idols are retained for human consumption by subsistence fishermen on a limited basis. They are primarily used as a popular pet in home aquariums with increased interest since the release of the movie Finding Nemo with a Moorish Idol named Gill being one of Nemo’s tank mates and of the movie Finding Dory with a Moorish Idol as an Easter egg. They are very active and very colorful, however, they are exceedingly difficult to raise and maintain requiring very large tanks and being very finicky eaters. In smaller aquariums they become highly aggressive and do not survive. They have been banned from importation into many European countries. The Moorish Idol is a direct descendant of the extinct Eozanclus brevirostris, which dates to the Eocene Period, 56 million to 34 million years ago.
Moorish Idol, Zanclus cornutus. Fish provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, March 2010. Length: 10.5 cm (4.1 inches). Note that the philomantis extension of the dorsal fin is black which is atypical of Zanclus cornutus and indicative that this might document the existence of at least two sub-species. Identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, CA.
Moorish Idol, Zanclus cornutus. Fish provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, May 2012. Length: 11.5 cm (4.5 inches).
Moorish Idol, Zanclus cornutus. Underwater photo taken in coastal waters off Kailua-Kona, HI, April 2015. Length: 20 cm (7.9 inches). Photo courtesy of Bob Hillis, Ivins, UT. Note the traditional white philomantis extension versus the black philomantis extension in the first two fish presented above. Personally I see these as documentation of the existance of two subspecies of Zanclus cornutus.