Description

The Bluespine Unicornfish (Naso unicornis) is a truly impressive and large species of tang, renowned for its distinctive “horn” that develops on its forehead as it matures. While fascinating, its immense adult size makes it suitable for only the largest home aquariums or public aquariums.

Here’s a comprehensive care guide for the Bluespine Unicornfish:

Appearance:

• Coloration: Generally blue-green to olive in color, often with a blue edge on the dorsal and anal fins. Two bright blue dots typically appear at the base of the caudal (tail) fin, near the peduncle spines.
• The Horn: The most distinguishing feature is the bony, tapering horn that develops on the forehead as the fish matures (usually when it reaches around 6 inches). This horn projects anteriorly at eye level but does not extend in front of the mouth. The purpose of the horn is believed to be related to social interactions and dominance displays.
• Caudal Spines: Like other surgeonfish, they possess two large, permanently erect, knife-like spines on each side of their caudal peduncle (tail base). These are highlighted in blue and are used for defense.

Adult Size:

• This is a critical factor for the Bluespine Unicornfish. In the wild, they can reach a massive size of up to 70 cm (28 inches or over 2 feet!) in length. While they may not reach this full size in most home aquariums, they will still grow very large, commonly reaching 50 cm (20 inches) or more.

Natural Habitat and Distribution:

• Found throughout the Indo-Pacific region, including the Red Sea, East Africa, and extending to the Hawaiian, Marquesas, and Tuamoto islands, north to southern Japan, and south to Lord Howe and Rapa islands (which includes waters around Australia).
• Inhabit channels, moats, lagoons, and seaward reefs, often in areas with strong surge. They are typically found at depths ranging from 1 to 180 meters.
• Mainly diurnal, they primarily feed on coarse, leafy brown algae like Sargassum in the wild.

Aquarium Care (Expert Level – Demands Extremely Large Tanks):

• Minimum Tank Size: This is the most significant hurdle. Due to their immense adult size and active swimming nature, a minimum of 360 gallons (approximately 1360 liters) is stated by many experts, with 500 gallons or more being truly ideal for long-term health and preventing stunting and stress. They need ample open swimming space. The tank should ideally be longer than it is tall.
• Water Parameters: Maintaining pristine and highly stable water quality is essential for all tangs, and especially for a fish of this size and activity level.
  • Temperature: 72-78F (22-26C)
  • Salinity: 1.020-1.025 specific gravity
  • pH: 8.1-8.4
  • Alkalinity: 8-12 dKH
  • Ammonia and nitrites must be 0 ppm. Nitrates should be kept as low as possible, ideally below 10 ppm.
• Filtration: A robust and oversized filtration system, including a powerful protein skimmer, is absolutely mandatory to handle their large bio-load and maintain water quality.
• Water Flow: They require strong, turbulent water flow to mimic their natural reef environment. Multiple powerheads or wavemakers are necessary.
• Diet:
  • Primarily herbivorous, constantly grazing on algae in the wild. They need a high-quality, varied diet rich in marine-based algae and seaweed.
  • Offer dried seaweed (nori) tied to a rock or using a veggie clip multiple times a day (at least 3 times per week, ideally daily).
  • Supplement with high-quality algae-based pellets and flakes (e.g., Spirulina-rich foods).
  • They are also known to eat zooplankton, so some frozen meaty foods like mysis shrimp or krill can be offered as a supplement, but plant matter should form the bulk of their diet.
  • Frequent small feedings (3-4 times a day) are best to support their high metabolism and constant grazing. A well-fed tang is less prone to aggression and diseases like HLLE (Head and Lateral Line Erosion).
• Temperament:
  • Generally considered peaceful towards other non-tang species after they establish their place in the pecking order.
  • Aggressive towards other tangs, particularly conspecifics (other Naso species) and similarly shaped surgeonfish. It is generally recommended to keep only one Bluespine Unicornfish per tank. If attempting to keep multiple tangs in an extremely large system, they should be introduced simultaneously and ideally be of different genera and body shapes.
• Reef Compatibility: Generally considered reef safe. They primarily graze on macroalgae and are unlikely to bother corals or most invertebrates, but like all tangs, if not fed adequately, they may nip at certain large polyp stony (LPS) corals.
• Tank Setup:
  • Provide ample live rock with numerous hiding places and structures to graze upon.
  • Crucially, ensure vast open swimming areas in the water column.
  • A robust and secure lid is essential as they are powerful jumpers, especially when startled.
  • A well-established aquarium (at least a year old) with stable water parameters is non-negotiable.
• Disease Susceptibility: While generally hardy once established, like all tangs, they can be susceptible to marine ich (Cryptocaryon irritans) if stressed or in poor water quality.
• Acclimation: Proper and slow acclimation (drip acclimation) is absolutely essential.

• Availability: Due to their size requirements, Bluespine Unicornfish may not be readily available in all local fish stores. You might need to special order them from a reputable marine wholesaler.
• Logistics: Transporting and housing such a large fish requires significant planning and equipment.
• Long-Term Commitment: This is a long-lived species (up to 55 years in the wild). Acquiring one is a commitment to providing a suitable environment for many years.

The Bluespine Unicornfish is a magnificent and truly impressive marine fish. However, its immense adult size and demanding care requirements mean it should only be considered by expert aquarists with very large, dedicated aquariums and a strong commitment to providing optimal conditions.