Acanthurus nigrofuscus (Dusky Tang / Lavender Tang)
• Small fish safe: ✅ Yes
• Small invert safe: ✅ Yes
• Coral safe: ✅ Yes
• Minimum tank size: 350L+
• Adult size: ~21 cm
• Diet: Herbivorous (marine algae, seaweed, spirulina-based flakes/pellets, occasional meaty foods)
• Be aware of: Can be territorial towards other tangs, especially those in the Acanthurus genus. Requires frequent feeding with marine algae to maintain health. Hardy but susceptible to ich if stressed.
Dusky Tang (Acanthurus nigrofuscus) – A Hardy and Underrated Algae Grazer
The Dusky Tang, also known as the Lavender Tang, is a medium-sized surgeonfish found throughout the Indo-Pacific region. It is known for its subtle but elegant coloration, algae-grazing behaviour, and peaceful temperament, making it an excellent choice for marine aquarists looking for an effective herbivore. Though less flashy than some other tang species, the Dusky Tang is a hardy and adaptable fish that thrives in reef tanks.
Appearance and Coloration
The Dusky Tang has a unique, muted colour palette compared to other surgeonfish. Its body is a mix of brown, grey, and lavender hues, which can appear slightly iridescent under aquarium lighting. The body may have faint vertical striations, and the tail is often darker than the rest of the body. Like all surgeonfish, it features a sharp, defensive scalpel-like spine at the base of its tail, which it uses for protection.
While not as brightly coloured as a Yellow Tang or Achilles Tang, the Dusky Tang’s graceful movement and subtle beauty make it a striking addition to a reef tank.
Natural Habitat and Behaviour
Dusky Tangs are commonly found in shallow lagoons, coral reefs, and coastal reef slopes, often at depths between 2 to 30 metres. They are active swimmers and constant grazers, feeding on algae-covered rock surfaces throughout the day.
In captivity, they:
• Swim actively, preferring plenty of open space.
• Graze continuously, making them excellent algae controllers.
• Are generally peaceful, but can be territorial towards other tangs, especially those of similar size and shape.
They are best kept as the only Acanthurus tang in a mid-sized tank, unless the aquarium is large enough to support multiple tang species.
Tank Requirements and Water Parameters
Dusky Tangs are active swimmers that require moderate to large aquariums with ample space for movement.
• Minimum tank size: 350L+ (larger recommended for long-term care)
• Temperature: 23–26°C
• pH: 8.1–8.4
• Salinity: 1.020–1.025
• Water movement: Moderate to strong, mimicking natural reef currents
• Filtration: High-quality filtration and protein skimming recommended
Live rock should be provided to encourage natural grazing behaviour, as they will scrape algae and detritus from the surfaces.
Diet and Feeding
Dusky Tangs are primarily herbivores, feeding on macroalgae and planktonic material in the wild. To keep them healthy, a high-fiber diet rich in marine algae is essential.
Recommended foods include:
• Dried seaweed (Nori) – Essential for digestion and overall health
• Spirulina-based flakes and pellets – Provides necessary vitamins and nutrients
• Fresh macroalgae – Such as chaetomorpha or gracilaria
• Occasional meaty foods – Enriched brine shrimp or mysis shrimp (as a supplement only)
They should be fed multiple times per day, as they are natural continuous grazers. A diet lacking in algae can lead to nutritional deficiencies, stress, and health problems.
Compatibility and Tank Mates
The Dusky Tang is generally peaceful, but like all tangs, it can be territorial, especially toward other herbivores or tangs in the Acanthurus genus.
Best tank mates include:
✔ Clownfish
✔ Wrasses (Fairy Wrasses, Halichoeres species)
✔ Gobies and blennies
✔ Angelfish (both dwarf and large species)
✔ Other peaceful to semi-aggressive reef-safe fish
Avoid housing with:
❌ Other Acanthurus tangs unless in a very large tank
❌ Very aggressive tang species (e.g., Sohal Tang, Clown Tang)
❌ Slow-moving fish that may struggle to compete for food
If keeping multiple tangs, they should be introduced simultaneously in a large system to minimize aggression.
Health and Disease Considerations
Dusky Tangs are hardy, but like all tangs, they are prone to common saltwater fish diseases, including:
• Marine ich (Cryptocaryon irritans) – Often caused by stress or sudden changes in water conditions. Quarantine before adding to the main tank is recommended.
• Head and Lateral Line Erosion (HLLE) – Can occur if their diet lacks algae or if water quality is poor.
• Nutritional deficiencies – If not provided with enough marine algae, they may develop digestive problems and faded coloration.
To maintain optimal health:
✔ Ensure a diet rich in marine algae and vegetable matter.
✔ Maintain stable water conditions to prevent stress-related illnesses.
✔ Quarantine new fish before adding them to the main system.
Lifespan and Long-Term Care
With proper care, Dusky Tangs can live up to 10-12 years in captivity. Their resilience, algae-eating habits, and peaceful temperament make them a great choice for medium to large reef tanks.
Why Choose a Dusky Tang?
✔ Great for mid-sized reef tanks – Smaller than many other Acanthurus tangs.
✔ Excellent algae grazer – Helps control nuisance algae in the aquarium.
✔ Generally peaceful – Easier to keep in a community tank.
✔ Hardy and adaptable – More forgiving than some other tang species.