Bluetail Unicornfish

The Bluetail Unicornfish, Naso caeruleacauda, is a distinctive and relatively uncommon surgeonfish recognized by its streamlined bluish-gray to brownish-gray body and vivid blue caudal fin. Subtle yellow coloration may appear along the lower body and beneath the pectoral-fin area, while its clean, elongated profile gives it a graceful appearance in large marine displays. Unlike many familiar unicornfish, this species does not develop a prominent forehead horn.

Native primarily to the Western Central Pacific, including the Philippines, Indonesia, and northern portions of the Great Barrier Reef, Naso caeruleacauda is associated with deeper outer reef slopes. In nature it commonly forms schools that move above the reef in pursuit of zooplankton, making it a highly active, open-water swimmer rather than a fish that spends all of its time grazing rock surfaces.

For experienced aquarists with exceptionally spacious systems, the Bluetail Unicornfish can become an impressive centerpiece in either a large reef aquarium or fish-only aquarium. Its bold blue tail, substantial adult size, and continuous swimming behavior make it especially well suited to long aquariums designed around active marine fish.

Quick Care Guide

Care Level: Expert Only
Minimum Tank Size: 350 gallons
Temperament: Semi-aggressive
Diet: Planktivore / Omnivore
Reef Safe: Yes
Region: Western Central Pacific – Philippines, Indonesia, and northern Great Barrier Reef
Scientific Name: Naso caeruleacauda

Tank Requirements

A large, elongated aquarium with extensive open swimming room is essential. Adults reach approximately 40 cm standard length, or about 16 inches excluding the tail, and their active open-water behavior requires substantially more space than their body length alone might suggest.

Arrange live rock primarily along the back and sides of the aquarium to provide sheltered areas while maintaining long, unobstructed swimming lanes. Caves and overhangs provide useful resting areas, but dense rockwork that restricts movement should be avoided.

Moderate to strong water movement, excellent oxygenation, and robust filtration are recommended. This species naturally inhabits outer reef environments and benefits from clean, well-circulated water. A secure cover is also advisable, particularly while a newly introduced specimen is acclimating.

Long-term housing should be planned carefully before purchase. This is a powerful, continuously swimming surgeonfish intended for very large marine systems rather than conventional community reef aquariums.

Diet and Feeding

Unlike many surgeonfish that rely heavily on benthic algae, the Bluetail Unicornfish is strongly associated with zooplankton feeding in the wild. Captive diets should therefore include frequent offerings of nutritious marine-based meaty foods while still providing vegetable matter appropriate for a surgeonfish.

Offer mysis shrimp, enriched brine shrimp, copepod-based foods, finely chopped marine seafood, and high-quality frozen plankton blends. Quality marine pellets can also be introduced once the fish is feeding confidently.

Supplement the diet with spirulina-based foods and marine algae sheets such as nori to provide additional plant material and dietary variety.

Several smaller feedings throughout the day are preferable to a single large feeding, particularly for established specimens accustomed to feeding regularly from the water column.

Temperament and Tankmates

The Bluetail Unicornfish is generally best considered semi-aggressive. It is typically compatible with appropriately sized reef fish but may become territorial toward other surgeonfish, particularly other Naso species or fish occupying a similar ecological niche.

Keep only one Bluetail Unicornfish unless maintaining an exceptionally large system specifically designed for multiple large surgeonfish. Introducing tangs simultaneously and providing abundant swimming space can reduce territorial disputes, but compatibility cannot be guaranteed.

Good tankmates include robust peaceful and semi-aggressive marine fish that will not intimidate it or compete excessively for food. Very timid species may be uncomfortable around a large, constantly moving adult.

Reef Compatibility

The Bluetail Unicornfish is considered reef safe and is not normally a threat to healthy corals, clams, ornamental shrimp, crabs, or snails. Its natural feeding behavior is focused primarily on planktonic foods rather than sessile reef invertebrates.

Because adults are strong swimmers with substantial body mass, coral structures and rockwork should be firmly secured. Accidental contact from a large specimen can dislodge loosely mounted corals even though the fish is not deliberately feeding on them.

Water Parameters

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

Prioritize stable salinity, strong oxygenation, low accumulated waste, and consistent water quality rather than attempting to chase exact parameter values.

Common Considerations

• Very large aquarium required: Its adult size and continuous open-water swimming behavior make substantial tank length and swimming volume essential.

• Plankton-focused feeding: Provide frequent mysis, copepod, plankton, and other appropriately sized marine foods rather than treating it strictly as an algae-grazing tang.

• Surgeonfish aggression: Use caution when combining it with other Naso species or similarly shaped tangs.

• Strong oxygenation: Active swimming and an outer-reef lifestyle make excellent circulation and dissolved oxygen particularly important.

• Caudal defensive blade: Like other surgeonfish, it possesses a sharp structure on the caudal peduncle and should be handled carefully.