- Common name
- Achilles tang
- Scientific name
- Acanthurus achilles
- Category
- Marine fish
- Group
- Surgeonfishes and tangs
- Environment
- Marine reef aquarium
- Origin
- Oceanic islands of the tropical Pacific from Oceania to Hawaii and Pitcairn, plus offshore eastern-central Pacific islands and the southern tip of Baja California
- Care level
- Expert
- Adult size
- Up to 24 cm total length
- Expected lifespan
- Decades-long commitment: wild individuals have been aged from 0 to 39 years.
- Minimum housing
- At least 680 L with a 180 cm or longer footprint, powerful oxygenation and strong surge-like flow
- Temperature
- 24–27 °C
- pH
- 8.1–8.4
- Hardness / minerals
- Alkalinity 7–11 dKH; calcium 380–450 mg/L; magnesium 1,250–1,400 mg/L
- Salinity
- 33–36 ppt; specific gravity about 1.024–1.027
- Lighting
- Normal reef lighting with open, well-oxygenated swimming space
- Placement / zone
- Open middle water and exposed reef faces
- Filtration
- Use oversized mature reef filtration, aggressive skimming and accessible mechanical capture sized for a large continuously fed herbivore. Maintain stable measurable nutrients without allowing ammonia, nitrite or suspended waste.
- Aeration
- Provide exceptional gas exchange and broad high-energy circulation with backup aeration. Oxygen demand is high and any rapid breathing, surface hovering or loss of grazing requires immediate investigation.
- Maintenance
- Feed and observe several times daily, remove waste, clean mechanical prefilters frequently, trend nitrate and phosphate, inspect skin and fins, and maintain open swim lanes and surge-like flow.
Identity and search names
Species-level profile for Acanthurus achilles. Juveniles lack the full adult orange caudal patch, and occasional hybridisation with A. nigricans means provenance matters.
Search names: redspot surgeonfish
Environment and housing
A mature high-energy reef aquarium with a long open swimming lane, strong random flow, exceptional oxygenation and secure rockwork
Social structure: Keep singly in ordinary home aquariums
Feeding and nutrition
Feeding ecology: Filamentous and small fleshy algae; marine algae sheets and quality herbivore foods in captivity
Feeding routine: Multiple small plant-rich feedings daily with continuous grazing opportunity
Breeding, reproduction or spread
Paired pelagic broadcast spawning in nature; routine home-aquarium breeding is not established
Parental care: None after spawning
Detailed care and app-ready planning
- Identity scope
- Species-level profile for Acanthurus achilles. Juveniles lack the full adult orange caudal patch, and occasional hybridisation with A. nigricans means provenance matters.
- Adult size and space
- Plan for 24 cm total length and relentless swimming. Use at least 680 L with a 180 cm or longer footprint, open lanes and surge-like circulation.
- Social structure
- Keep singly in ordinary home aquariums. Wild grouping does not make multiple tangs safe in a confined aquarium.
- Swimming zone or placement
- Open middle water and exposed reef faces, with unobstructed horizontal movement.
- Feeding ecology
- A grazer of filamentous and small fleshy algae on high-energy reefs.
- Feeding plan
- Provide marine algae sheets and quality herbivore foods in several small feedings daily, plus limited marine protein. Maintain constant grazing opportunity.
- Water stability
- Maintain 24–27 °C, pH 8.1–8.4, salinity 33–36 ppt, alkalinity 7–11 dKH, calcium 380–450 mg/L and magnesium 1,250–1,400 mg/L. Oxygen and gas exchange must remain exceptional.
- Habitat structure
- Use a long mature reef with secure rockwork, open swimming lanes and strong broad random flow rather than narrow jets.
- Compatibility plan
- Avoid other Acanthurus and similar-shaped tangs in ordinary systems. Choose robust fish that will not block grazing or compete aggressively.
- Breeding or reproduction plan
- Pelagic pair spawning is documented in nature. Home-aquarium breeding is not established, so do not offer generic spawning instructions as a practical plan.
- Quarantine
- Quarantine in a large, highly oxygenated bare system with shelter and continuous plant-rich feeding. Monitor closely for ectoparasites and stress.
- Welfare checks
- Check respiration, grazing, body condition, skin, fins, pacing, collision injuries and aggression. Handle carefully because the caudal spine can injure people and fish.
- Biosecurity and release
- Never release fish or aquarium water. Verify current BICON, Live Import List and state rules before import or movement.
- Main risk
- Insufficient oxygen, flow and permanent swimming space are the main welfare risks.
- Adult projected load
- A 24 cm, constantly swimming, frequently fed grazer creates a high adult oxygen and nutrient load. Size the aquarium, skimmer, circulation, algae supply and maintenance for the mature fish, not a juvenile tang.
- Filtration
- Use oversized mature reef filtration, aggressive skimming and accessible mechanical capture sized for a large continuously fed herbivore. Maintain stable measurable nutrients without allowing ammonia, nitrite or suspended waste.
- Aeration
- Provide exceptional gas exchange and broad high-energy circulation with backup aeration. Oxygen demand is high and any rapid breathing, surface hovering or loss of grazing requires immediate investigation.
- Maintenance
- Feed and observe several times daily, remove waste, clean mechanical prefilters frequently, trend nitrate and phosphate, inspect skin and fins, and maintain open swim lanes and surge-like flow.
- Overridable warnings
- Non-overridable: do not keep this species without the adult 180 cm swimming footprint, exceptional oxygenation, continuous plant-based feeding and a quarantine plan. Alternative equipment or aquascape is acceptable only when those performance outcomes are objectively met.
Compatibility, welfare and risk
Compatibility: Robust reef fish only; avoid similar-shaped surgeonfishes except in exceptionally large expert-managed systems
Welfare: Rapid breathing, loss of grazing, repeated pacing, colour deterioration, white spots or collision injuries require immediate correction
Main warning: Extreme oxygen and swimming-space demand, parasite susceptibility, aggression and a sharp caudal spine
Biosecurity and release
Use legally sourced stock. Verify current BICON, Live Import List and state requirements. Never release marine fish or aquarium water.