Goldrim Surgeonfish, Acanthurus nigricans

Goldrim Surgeonfish, Acanthurus nigricans. Underwater photograph taken in coastal waters of the greater Los Cabos area, Baja California Sur, May 2018. Photograph courtesy of Bob Hillis, Ivins, Utah.

Goldrim Surgeonfish, Acanthurus nigricans. Underwater photograph taken in Zihuantanejo Bay, Guerrero, March 2018. Photograph courtesy of Ron Woheau, Zihuantanejo.

Goldrim Surgeonfish, Acanthurus nigricans. Underwater photograph taken in Zihuantanejo Bay, Guerrero, January 2019. Photograph courtesy of Maude Jette, Dive Zihuantanejo,   www.Divezihuantanejo.com.

The Goldrim Surgeonfish, Acanthurus nigricans, is a member of the Surgeonfish or Acanthuridae Family, that is also known as the Whitecheek Surgeonfish and in Mexico as cirujano cariblanco. Globally, there are forty-two species in the genus Acanthurus, of which seven are found in Mexican waters, three in the Atlantic and four in the Pacific Ocean.

The Goldrim Surgeonfish have elongated and highly compressed bodies. They are blue-black or black with large white blotches below their eyes, a narrow white band that encircles their mouth, a yellow band that widens posteriorly at the base of their anal and dorsal fins, and a white caudal fin with narrow yellow bars posteriorly. They have a steep head profile, a small protrusible mouth set low on their head, and 8 to 28 flattened teeth on each jaw. Their anal fin has 3 spines and 26 to 29 rays; their caudal fin is concave; and, their dorsal fin is continuous with 9 spines and 28 to 31 rays. They have a short caudal peduncle with a single razor-sharp spine on each side. They have 17 to 19 gill rakers. Their body is covered with tiny rough scales. Their lateral line is complete.

The Goldrim Surgeonfish is found around and within shallow and rocky coral reefs at depths up to 200 m (660 feet). They reach a maximum of 22.0 cm (8.7 inches) in length with females being consistently larger than males. They prefer water temperatures between 21ºC (70ºF) and 29ºC (84ºF). They feed almost exclusively on filamentous algae and small amounts of detritus and are classified as grazers. All developmental stages (eggs, larvae, juveniles, and adults) are preyed upon by larger fish. They are active diurnally and can be found as solitary individuals or in small and large mixed-species schools. The smaller juveniles take refuge within large corals. They are oviparous with annual breeding cycles. They are broadcast spawners and release pelagic eggs that are fertilized externally. They have a lifespan of34 years with females living longer than males. The Goldrim Surgeonfish is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.

The Goldrim Surgeonfish is a resident of Mexican waters of the Pacific Ocean but have a limited distribution being found along the east coast of Baja and along the coast of the mainland from Mazatlán, Sinaloa to Acapulco, Guerrero, however, they are rare when compared to their populations in the Western Pacific Ocean.

The Goldrim Surgeonfish is one of the smaller Surgeonfish but has a similarly shaped body profile than several other Surgeonfish found in similar locations, however, the markings of the Goldrim are such that it cannot be confused with any other species.

From a conservation perspective the Goldrim Surgeonfish is currently considered to be of Least Concern with stable and widely distributed populations. They are subject to local overfishing by artisanal subsistence fishermen and by coral reef habitat degradation. They play an important ecological role by consuming algae that would otherwise kill coral reefs. The Goldrim Surgeonfish are not a significant food fish due to their size but they are retained by subsistence fishermen. They are also utilized by the aquarium trade and can be purchased on the internet.

A word of caution. The spines at the tail base of this fish provide a unique defense mechanism and can inflict major slashing wounds, rendering them dangerous to handle.