Convict Surgeonfish, Acanthurus triostegus
Convict Surgeonfish, Acanthurus triostegus. Fish caught with a cast net, quickly photographed and returned to its native environment unharmed from coastal waters off Los Cabos, Baja California Sur, April 2021. Length: 9.5 cm (3.7 inches).
Convict Surgeonfish, Acanthurus triostegus. Fish caught from coastal waters off He’eia, Oahu, Hawaii, February 2016. Length: 15.2 cm (6.0 inches). Catch, photograph and identification courtesy of Kenneth Tse, Toronto, Canada.
Convict Surgeonfish, Acanthurus triostegus. Underwater photo taken in the greater Cabo San Lucas area, Baja California Sur, November 2017.
Convict Surgeonfish, Acanthurus triostegus. Underwater photo taken in the greater Cabo San Lucas area, Baja California Sur, November 2017.
Convict Surgeonfish, Acanthurus triostegus. Underwater photograph taken in Zihuantanejo Bay, Guerrero, March 2018. Photograph courtesy of Ron Woheau, Zihuantanejo.
Convict Surgeonfish, Acanthurus triostegus. Underwater photograph taken in coastal waters of the greater Los Cabos area, Baja California Sur, May 2018. Photograph courtesy of Bob Hillis, Ivins, Utah.
Convict Surgeonfish, Acanthurus triostegus. Underwater photograph taken in Zihuantanejo Bay, Guerrero, January 2019. Photograph and identification courtesy of Maude Jette, Dive Zihuantanejo, www.Divezihuantanejo.com.
The Convict Surgeonfish, Acanthurus triostegus, is a member of the Surgeonfish or Acanthuridae Family, that is also known as the Convict Tang and known in Mexico as cirujano reo. 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 Convict Surgeonfish has a deep oval highly compressed body with a depth that is 50% to 52% of standard length. They are light olive to almost white in color. They have 6 vertical black stripes on their sides: 1 on their head passing through their yellow eyes, 4 on their body, and 1 at the base of their caudal fin. Males and females are very similar in appearance, although males assume courtship colors when breeding. Juveniles lack the bars found in adults. They have a steep head profile with eyes located high on the head. They have a small mouth low on the head and a protrusible jaw with serrated teeth on both sides. Their anal fin has 3 spines and 19 to 22 rays; their caudal fin is slightly concave; and, their dorsal fin has 9 spines and 22 to 26 rays. They have short caudal peduncles and the razor sharp peduncle spines are rather small when compared to those of other tangs. They have 18 to 22 gill rakers in the anterior row and 19 to 24 gill rakers in the posterior row. Their body is covered with tiny, rough, and tightly-spaced scales. Their lateral line is complete.
The Convict Surgeonfish is found in shallow and wave-affected areas in and around coral reefs at depths up to 90 m (300 feet) with juveniles taking up residence in tidal pools and coral reefs. They reach a maximum of 27 cm (11 inches) in length. They prefer water temperatures between 24ºC (75ºF) and 26ºC (79ºF). They feed primarily on algae and are classified as grazers. They also consume benthic invertebrates on a limited basis. All developmental stages (eggs, larvae, juveniles, and adults) are preyed upon by larger fish, such as eels, groupers, snappers, and various other marine animals. They can be found as solitary individuals or in small and large schools. They can detect vibrations and possess a strong sense of smell and sound. They utilize large schools and disruptive color patterns as defense mechanisms. They can also feign death by exhibiting tonic immobility to avoid predation. They are hosts to symbiotic unicellular organisms in their gut, including one of the largest known bacterial species, Epulopiscium fishelsoni. They also host endoparasitic nematodes and trematodes, as well as at least one ectoparasitic copepod species. They are oviparous with annual breeding cycles that include large spawning aggregations numbering up to tens of thousands of fish. They are broadcast spawners with the release of pelagic eggs that are fertilized externally. During spawning, clouds of eggs and sperm are preyed upon by various predatory fish. Eggs develop rapidly and hatch into clear pelagic larvae. The larvae transition into juvenile within three months, which settle out within the reef or in tidal pools. As they mature they eventually leave the tidal pools and roam in the reefs until they join schooling groups. Adults provide no parental care to their offspring. They have lifespans of seven years in captivity; their lifespan in the wild has not been determined. The Convict 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 Convict Surgeonfish is a resident of Mexican waters of the Pacific Ocean but has a limited distribution being found from La Paz southward to Cabo San Lucas, Baja California Sur, along the southeast coast of Baja and from Mazatlán, Sinaloa, southward to Guatemala along the coast of the mainland.
The Convict Surgeonfish cannot be confused with any other species due to its light-colored body and pattern of dark bars on the sides.
From a conservation perspective the Convict Surgeonfish is currently considered to be of Least Concern with stable, widely distributed populations. In some locations they are of concern due to overfishing and in others due to the loss of coral reef area and coral reef habitat. The Convict Surgeonfish are utilized as a food source by many cultures and are fished commercially. They are also targeted by recreational fishermen in some locations. They are considered quality food fish in some areas but in other areas are known to contain ciguatoxin. They are a popular fish in the aquarium trade. However, they require aquarium sizes of at least 75 gallons and are hostile towards other fish. They are available online at prices between $22.95 and $49.99 per fish.
A word of caution. The spines found at their tail base provide these fish with a unique defense mechanism rendering them dangerous to handle as these spines can inflict major slashing wounds.