Convict Tang

The Convict Tang (Acanthurus triostegus) is a distinctive saltwater fish recognized by its silvery-white to pale gray body crossed by bold vertical black bars. One stripe passes directly through the eye, while additional dark bands continue across the body and caudal peduncle, creating the unmistakable pattern responsible for its common name. Its clean coloration, constant grazing activity, and streamlined profile give it a very different appearance from more brightly colored surgeonfish.

Widely distributed across the Indo-Pacific and into the eastern Pacific, this species naturally inhabits lagoon and seaward reefs, where it frequently grazes hard substrates covered in filamentous algae. Convict Tangs may form substantial feeding groups in the wild, moving across reef flats and rocky areas in search of fresh algae.

Compared with many members of the Acanthurus genus, the Convict Tang is often relatively tolerant of other community fish, although territorial behavior with other surgeonfish can still occur. Its active grazing behavior, coral-safe nature, and attractive schooling tendencies make it an appealing choice for a large reef aquarium or fish-only marine aquarium with ample swimming space.

Quick Care Guide

Care Level: Moderate
Minimum Tank Size: 125 gallons
Temperament: Semi-aggressive
Diet: Herbivore
Reef Safe: Yes
Region: Indo-Pacific and Eastern Pacific
Scientific Name: Acanthurus triostegus

Tank Requirements

A 125-gallon or larger established saltwater aquarium is recommended for long-term care. Adults can exceed 10 inches, and this species is an active swimmer that spends much of the day moving between open water and grazing areas.

Provide substantial live rock or other mature reef structure for natural algae growth while preserving long, unobstructed swimming areas. An aquascape with caves and protected retreats gives the fish somewhere to shelter at night or when startled without restricting its daytime movement.

Moderate to strong water movement and excellent oxygenation are appropriate. Efficient filtration is also important because tangs require frequent feeding and can contribute substantially to the aquarium's nutrient load.

A mature aquarium with established algae growth is particularly beneficial. A secure aquarium cover is recommended, especially during acclimation.

Diet and Feeding

The Convict Tang is primarily herbivorous and naturally spends much of the day grazing filamentous algae from rock and reef surfaces. A diet rich in marine vegetable matter is essential for maintaining proper body condition.

Offer dried nori or other marine seaweed daily or very frequently using a feeding clip. Supplement this with quality herbivore pellets, spirulina-based foods, frozen herbivore blends, and other marine algae preparations.

Mysis shrimp, enriched brine shrimp, and other meaty foods may be eaten when offered to tankmates, but these should remain supplemental rather than forming the foundation of the diet.

Multiple small feedings and regular access to grazing material are preferable to one large meal. Convict Tangs can lose body condition if insufficient vegetable matter is available, so monitor the abdomen and overall body profile carefully.

Temperament and Tankmates

The Convict Tang is generally less territorial than many other surgeonfish but should still be considered semi-aggressive, particularly when interacting with other tangs.

It typically mixes well with clownfish, angelfish, wrasses, rabbitfish, anthias, gobies, blennies, and other appropriately sized marine community fish.

Convict Tangs naturally associate in groups and can sometimes be maintained with their own species in very large aquariums. When keeping multiple individuals, introducing them together and providing extensive swimming space and multiple feeding areas can help reduce territorial disputes.

Other surgeonfish should be introduced cautiously. Individual temperament varies, and established tangs may challenge newcomers over swimming territory or access to food.

Reef Compatibility

The Convict Tang is considered reef safe and does not normally consume healthy SPS corals, LPS corals, soft corals, clams, shrimp, snails, or other established ornamental invertebrates.

Its grazing behavior is primarily directed toward filamentous and film algae growing on rock and other hard surfaces. This constant grazing makes the species particularly appealing in larger reef aquariums.

Loosely mounted coral frags should still be secured, as an active adult tang can accidentally dislodge small pieces while swimming or grazing around the aquascape.

Water Parameters

Temperature: 75–80°F
Specific Gravity: 1.024–1.026
pH: 8.1–8.4
Alkalinity: 8–12 dKH

Maintain stable, well-oxygenated seawater and avoid sudden changes in temperature, salinity, or other major parameters. Consistent water quality is more important than maintaining one exact number within these ranges.

Common Considerations

• Adults can reach approximately 10 inches or slightly more and require substantial open swimming space.

• Marine algae and seaweed should make up the majority of the long-term diet.

• Although relatively tolerant for a surgeonfish, territorial behavior toward other tangs is still possible.

• Groups require considerably more space than a single specimen and should be introduced carefully.

• Like other surgeonfish, the Convict Tang has sharp caudal peduncle spines, so use caution during capture, handling, and transport.