Yellowfin Surgeonfish, Acanthurus xanthopterus
The Yellowfin Surgeonfish, Acanthurus xanthopterus, whose common Spanish name is cirujano aleta amarilla, is a species in the Surgeonfish or Acanthuridae Family, which are known collectively as cirujanos in Mexico. Globally, there are forty-two species in the genus Acanthurus, seven of which are found in Mexican waters, three in the Atlantic and four in the Pacific.
The Yellowfin Surgeonfish are the largest of the Surgeonfish. They have elongated oval compressed bodies, which are gray-blue and change to light blue ventrally. They have numerous irregular dark lines covering their sides. The outer third of their pectoral fins are yellow. The area around and in front of their eyes is yellow. Their caudal fin base often has a white bar. Their anal and dorsal fins feature alternating dark and light blue bars with dark margins and a pink tinge. Their caudal fin is strongly concave with an abundance of horizontal dark lines. They have a steep profile with eyes set high on their head and a small protrusible mouth placed low on their head with large flattened close-set teeth. Their anal fin has 3 spines and 23 to 25 soft rays; their dorsal fin is continuous with 9 spines and 25 or 27 rays; and their pelvic fins have one spine and 5 soft rays. A key to identification is the tail base, which has a large depressed spine that fits into a groove on the side of their caudal base. They have a complete lateral line and their body is covered with small rough scales.
The Yellowfin Surgeonfish are a coastal schooling species normally found in shallow waters over sandy substrate adjacent to coral and rocky areas at depths up to 400 feet. They reach a maximum length of 70 cm (28 inches). They feed diurnally and primarily on benthic algae. The Yellowfin Surgeonfish have been poorly studied and very little is known about their behavioral patterns.
The Yellowfin Surgeonfish have a wide global distribution being found in the Indian and Pacific Oceans. In Mexican waters, however, they have a limited distribution being found only in the extreme southern portion of the Sea of Cortez between La Paz and Cabo San Lucas and along the coast of the mainland from Acapulco south to Guatemala.
The Yellowfin Surgeonfish is an easy fish to identify due to its coloration and thus cannot be confused with any other species.
The Yellowfin Surgeonfish are fairly abundant in the southern extreme of the Sea of Cortez. They can often be seen in schools of up to 20 individuals in a chum line slowly moving toward the surface. They are very difficult to catch by hook and line requiring significant downsizing of hooks as they are very finicky nibblers. If hooked they become a fierce foe on light tackle. Upon collection they quickly changes from a gorgeous blue to an ugly dark blue-gray. They are considered good food fish, however, there is a concern that they may contain Cigua Toxin, which is present in Surgeonfish outside the Eastern Pacific. Caution: The spines found at their tail base provide these fish with a unique defense mechanism rendering them exceedingly “dangerous” to handle as these spines can inflict major slashing wounds. In addition, the base of their caudal fin has a truly lethal scalpel.
Yellowfin Surgeonfish, Acanthurus xanthopterus. Fish caught off Point Palmilla, Baja California Sur, April 2013. Length: 40 cm (16 inches). Note: this fish is a very difficult photography subject whose coloration fades very quickly from being truly gorgeous to an ugly pale tan.