Elongate unicornfish
Naso lopezi
The elongate unicornfish is a deep-water giant with an aerodynamic, elongated body. It requires a monumental aquarium system with minimal rockwork, allowing maximum space for its active swimming.
Water Temperature
24 - 28 °C
pH Value
8.1 - 8.4
Water type
Marine
Tank level
Middle
Adult size
60 cm
Minimum tank volume
>= 1,200 L
Minimum group
>= 1
Species description
Geographical Origin and Habitat: Naso lopezi, the elongate unicornfish, is native to the Western Indo-Pacific Ocean, with populations ranging from southern Japan down through the Philippines, Indonesia, and to the Great Barrier Reef in Australia. It primarily inhabits deep outer reef slopes, drop-offs, and seaward rocky walls at depths from 6 to 70 meters, swimming in loose schools in high-current zones.
Taxonomy and Morphology: Belonging to the family Acanthuridae and the genus Naso, this species does not grow the prominent forehead horn found on some of its relatives. It possesses a highly elongated, streamlined body shape designed for sustained open-water swimming. In the wild, it can reach an impressive maximum length of up to 60 centimeters (24 inches).
Social Behavior: Naso lopezi is an active, open-water swimmer that is generally peaceful towards other tankmates. In the wild, it forms schools to forage on zooplankton and macroalgae. In an aquarium, it is non-aggressive but can exhibit territorial behavior towards other large tangs if the tank size is insufficient.
Coloration and Sexual Dimorphism: The body coloration is a sleek silvery-grey to light blue, covered with numerous small, dark grey or black speckles on the upper half of the body. Sexual dimorphism is present; mature males grow significantly larger than females and develop long, elegant filaments on the upper and lower tips of their caudal fin.
Care, breeding and tankmates
Aquarium Setup: Due to its large size and active lifestyle, it requires a massive aquarium. A minimum tank size of 180 gallons (700 liters) is required for a juvenile, while adults need 300 gallons (1100 liters) or more. The aquascape should feature a minimal rock structure to maximize open swimming space, combined with powerful wavemakers.
Diet and Feeding: Although they feed on zooplankton in the wild, they require a diet heavy in vegetable matter in captivity. Offer dried seaweed (nori), spirulina, and specialized herbivore pellets daily, alongside frozen foods like mysis and krill to maintain body weight. Feeding multiple times a day is ideal.
Water Quality: High oxygen levels and clean water are vital. Strong filtration, a high-capacity protein skimmer, and a high turnover rate are necessary. Maintain a water temperature of 23 to 26 °C (73 to 79 °F), pH between 8.1 and 8.4, and a specific gravity of 1.020 to 1.025.
Compatibility and Cohabitation: This fish is reef-safe and does not harm corals or sessile invertebrates. It is peaceful towards smaller fish but should not be housed with aggressive, territorial tangs of the genus Acanthurus unless the aquarium is exceptionally large.
Aquarium Breeding: Breeding in home aquariums is not possible. They are pelagic spawners that release their eggs and sperm into the water column where the eggs drift with the currents. Rearing the larvae requires specialized setups only available in large public aquariums.
Risks and Diseases: Highly susceptible to marine ich (Cryptocaryon) and marine velvet under stress. It is also prone to Head and Lateral Line Erosion (HLLE) if its diet lacks sufficient nutrition or if low-quality activated carbon is used. Quarantine before introduction is strongly advised.
Geographic Origin and Distribution
Naso lopezi, the elongate unicornfish, is native to the Western Indo-Pacific Ocean, with populations ranging from southern Japan down through the Philippines, Indonesia, and to the Great Barrier Reef in Australia. It primarily inhabits deep outer reef slopes, drop-offs, and seaward rocky walls at depths from 6 to 70 meters, swimming in loose schools in high-current zones.
Origin
Cosmopolitan or introducedSouth and Southeast AsiaEast AsiaAustralia, New Guinea, and OceaniaTropical oceans and reefs
Fish profile
- Temperament
- Peaceful
- The Naso lopezi boasts a gentle giant temperament, being largely peaceful and highly personable with its human caretakers. Once acclimated, they often recognize their owners and will readily eat right from the aquarist's hand. They do not bother corals, invertebrates, or smaller fish, making them a centerpiece for giant reef tanks. Aggression is typically only displayed towards other large tangs or if they feel confined in a tank that is too small. Overall, they are majestic, calm, and highly rewarding fish for those with adequately sized systems.
- Diet
- Herbivore
- The Naso lopezi is primarily herbivorous, requiring a diet exceptionally rich in marine algae to thrive long-term. Dried nori or sea veggies should be offered daily, secured to a rock or a veggie clip for continuous grazing. They will also eagerly accept meaty offerings like mysis shrimp and krill, but meat should only make up a small portion of their diet. Providing spirulina-enriched flakes and pellets ensures they receive proper vitamins. A varied, algae-heavy diet prevents nutritional deficiencies and helps maintain their immune system.
- Life expectancy
- 10-15 years
- In a properly sized aquarium with meticulous care, Naso lopezi can reach a lifespan of approximately 10 to 15 years. The stability of water parameters and the absence of organic pollutants such as high nitrate levels are crucial factors for ensuring their longevity. A nutrient-rich diet enhanced with vitamins and trace elements helps strengthen their immune system against bacterial infections. A peaceful, low-stress environment significantly contributes to extending the life of this large surgeonfish.
- Adult size
- 60 cm
- The catalog's scalar value is 60 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 60 cm for this species, recorded as standard length (SL). The taxonomic record consulted is Naso lopezi (v25.04); male or unsexed record. These figures are not interchangeable: the first is the profile's editorial reference, whereas the second is a published maximum under a specific measurement convention; differences among sources can reflect sex, population, life stage and measuring method.
- Sex ratio
- Solitary
- Sexing the Naso lopezi is possible as they reach maturity, though it depends heavily on the specific species within the genus. Males often develop much larger and more prominent rostral horns or facial features compared to females. Furthermore, adult males may display elongated tail streamers (lyretails) which are absent or much shorter in females. Despite these differences, sexing is largely irrelevant for home aquarists since they are not bred in captivity. Keeping a single specimen or a known pair requires an enormous aquarium either way.
- Feeding frequency
- Twice daily
- Because of their constant grazing habits in the wild, the Naso lopezi needs to be fed multiple times per day. Having nori constantly available on a grazing clip is highly recommended to satisfy their instinct to forage. In addition to constant grazing, they should be offered prepared foods two to three times daily. This heavy feeding schedule is crucial to maintain their body weight and overall health. A well-fed Naso tang is more robust, less aggressive, and more resistant to common parasites like Cryptocaryon irritans.
- Bioload
- The Naso lopezi produces a massive bioload due to its large adult size and voracious herbivorous appetite. They consume massive amounts of plant matter and excrete proportionally large amounts of waste. A heavy-duty protein skimmer, mechanical filtration, and possibly a biological reactor are required to process their waste. Keeping water parameters pristine is essential, as large tangs are susceptible to lateral line disease if water quality degrades. Regular, high-volume water changes are an absolute necessity when housing this majestic fish.
- Flow
- Strong
- The Naso lopezi requires extremely strong, turbulent water flow to simulate the highly oxygenated reef drop-offs they inhabit in nature. They are incredibly strong swimmers and rely on heavy currents for exercise and proper respiration. Utilizing multiple high-capacity wavemakers or gyre pumps is necessary to keep water circulating aggressively. High flow also aids in keeping detritus suspended so the heavy filtration can remove it. Proper oxygenation driven by this flow is critical for their fast metabolism.
- Jump risk
- Yes
- Large and powerful, the Naso lopezi possesses a significant jump risk, especially during their initial acclimation period or if startled at night. Their sheer size and muscle mass mean they can easily launch themselves out of open-top aquariums. A sturdy, tightly fitted mesh cover is absolutely mandatory to prevent these expensive and beautiful fish from ending up on the floor. Heavy glass or acrylic lids can be used, but mesh is preferred to allow for maximum gas exchange. Minimizing sudden movements outside the tank also helps keep them calm.
- Reproduction
- Oviparous
- The Naso lopezi has not been successfully bred and reared in the home aquarium due to the complex requirements of their pelagic larvae. In the ocean, they participate in mass broadcast spawning events, releasing millions of eggs into the water column. The larvae undergo an extended pelagic phase before settling onto the reef as juveniles. Mimicking the physical space and specific dietary needs of the larvae is currently beyond the capabilities of standard captive environments. Therefore, all specimens in the trade are wild-caught.
- Compatibility & tankmates
- Peaceful
- Generally, the Naso lopezi is very peaceful toward completely different species and makes a fantastic addition to a large community reef aquarium. They are entirely reef safe and will actively graze on nuisance algae without bothering corals or motile invertebrates. However, they can show significant aggression toward other tangs, particularly those of the same genus or with a similar body shape. If keeping multiple surgeonfish, it is best to introduce them simultaneously into an oversized aquarium. They ignore smaller fish and peaceful tank mates completely.
- Tank level
- Middle
- An exceptionally large aquarium is absolutely mandatory for the Naso lopezi, with 200 gallons being the bare minimum for juveniles and 300+ gallons for adults. They are incredibly active and require massive, unobstructed swimming lanes spanning the entire length of the tank. The aquascape should be minimalist, utilizing island structures to maximize open water space while still providing large sleeping caves. Keeping them in cramped conditions causes severe stress, stunted growth, and behavioral issues. Providing adequate swimming room is the most critical aspect of their care.
Scientific Parameters & Models
FishBase
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 2.9 ± 0.33 se
- Resilience
- Medium (1.4 - 4.4 years)
- Phylogenetic uniqueness (PD50)
- 0.5
- Bayesian Length-Weight
- a = 0.02042, b = 2.93
- VulnerabilityModerate to high vulnerability (49 / 100)
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
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