Marine Aquarium Marine Fish Species Profiles, Surgeonfish Francesco Avezzano 12 August 2026 0 Comments

Acanthurus nigricauda: technical profile

Acanthurus nigricauda, belonging to the Acanthuridae family, is one of the least known but most intriguing species of tropical surgeonfish. Widespread in the warm waters of the Indo-Pacific, this herbivorous fish offers a unique combination of ecological function and discreet beauty, making it an ideal candidate for medium and large reef aquariums.

Often overlooked by newcomers in favour of more iconic species such as A. leucosternon or A. nigricans, the nigricauda (from the Latin for “black tail”) plays an essential role in keeping coral ecosystems in balance, thanks to its diet based on algal films and benthic detritus. Its generally less aggressive behaviour compared to other Acanthurus makes it particularly interesting for well-structured community aquariums.

From a taxonomic point of view, it is a sister species of A. xanthopterus and close to A. nubilus, with which it is sometimes confused in import markets. Its soft, tapered colouration, together with the typical black caudal bar, makes it unmistakable to the eyes of experienced enthusiasts.

In this guide we will analyse in detail every aspect of its profile: from its natural environmental requirements, to management in the aquarium, up to the ethical aspects linked to collection and to informed purchasing. A text conceived for those who do not just want to keep a fish, but to understand thoroughly its ecological role and the respect it deserves.

📛 Common name

Black-tailed surgeonfish
Double-bar surgeonfish
In the English-speaking world: Epaulette Surgeonfish, Blackbar Surgeonfish

🔁 Synonyms

Hepatus nigricauda (old synonym)
Some catalogues wrongly confuse it with Acanthurus auranticavus
In the past it was also described as a geographical variant of A. xanthopterus

🧪 Morphology

Acanthurus nigricauda presents a fusiform, laterally compressed body, typical of pelagic surgeonfish. It reaches considerable dimensions (over 40 cm in the wild) but in the aquarium it usually stops between 22 and 30 cm. The profile is dorsally arched, with a pointed snout suited to scraping surfaces.

✨ Distinctive elements:

Base colouration greyish-olive, sometimes light brown
Two horizontal black bands: one behind the eye, the other on the tail (hence the name)
Caudal peduncle armed with a sharp retractable blade
Long and arched dorsal and anal fins
Relatively large eye, in an advanced lateral position

The caudal fin is truncate or slightly emarginate, useful for swimming in open spaces or among turbulent currents. The scales are small but dense, and offer no particular protection, making it more vulnerable to parasites than other acanthurids.

Acanthurus nigricauda

♀️♂️ Differences between males and females

As with many Acanthurids, Acanthurus nigricauda does not present obvious sexual dimorphism. However:

Adult males, in the breeding phase, may display a slightly more contrasted livery
Some observe a greater curvature of the dorsal profile in dominant males

To identify the sex with certainty, gonadal examination would be necessary, which is only feasible in a zoological or university context.

🌿 Way of life

In the wild, this surgeonfish behaves as a grazing herbivore, moving both alone and in small mobile groups, often over sandy substrates or on reefs with rocky outcrops.

⏳ Activity: diurnal
📍 Territoriality: low, especially where there is ample space
🌐 Ecological function: contributes to the removal of microalgae, preventing the smothering of corals

It does not live permanently on a fixed territory, but adopts a behaviour known as a “feeding circuit”, that is, it follows circular routes during the day in order to graze without over-exploiting a single area.

🔥 Territoriality

Compared with A. nigricans or A. leucosternon, the nigricauda is much less aggressive, while still maintaining a slight defensive tendency towards conspecifics or towards surgeonfish similar in livery and shape.

🛑 Antagonism possible with:

A. nubilus
A. xanthopterus
A. mata

✅ High compatibility with:

Gobies
Centropyge
Frogfish
Small and peaceful wrasses

⏳ Life expectancy

In the wild it can reach 15–18 years, although in the aquarium it is difficult to exceed 7–10 years, especially without optimal conditions of:

Feeding
Water quality
Swimming space

The key to maximising longevity in captivity is to limit stress, offer a fibrous diet and crystal-clear water free from nitrogenous accumulations.

📏 Maximum size

📐 In the wild: up to 42 cm SL (standard length)
📐 In the home aquarium: generally between 20 and 30 cm, if well fed
📌 Rapid growth in the first 12–18 months, then stabilisation

A 25 cm specimen requires wide spaces and is not compatible with tanks under 600 litres.

🧾 Description

Elegant, understated and harmonious, Acanthurus nigricauda does not have the brilliance of other tangs, but it compensates with:

Marked and clean lines
A vaguely “military” appearance because of the dark bands
Fluid and hypnotic movement, much appreciated in mature reef tanks

It is a fish that “grows” visually with age: juveniles look more anonymous, but over time they take on a regal and authoritative bearing.

📉 Status on the IUCN red list

According to the International Union for Conservation of Nature (IUCN), Acanthurus nigricauda is currently classified as Least Concern (LC). This means that, in the current state of knowledge, there is no immediate risk of extinction for the species, even though localised threats do exist.

However, it is important to stress that this category may not accurately reflect the state of the population on coastal reefs, where human influence is greater. The IUCN itself points out that environmental changes such as:

Coral bleaching
Rising average ocean temperatures
Sedimentation from coastal construction
Organic pollution

can alter the availability of habitat and food resources, making even species so far considered stable vulnerable.

🌍 Habitat – Origin and geographical distribution

Acanthurus nigricauda has a wide but discontinuous distribution within the tropical Indo-Pacific, mainly in the following areas:

Red Sea and Gulf of Aden
Indian Ocean: Maldives, Sri Lanka, Seychelles
Central Indo-Pacific: Indonesia, Papua New Guinea
Western Pacific: Solomon Islands, Vanuatu, New Caledonia
Northern Australia and the Great Barrier Reef

📌 It is less common in Hawaii and entirely absent from the waters of the eastern Pacific (e.g. Galápagos).

Its preferred habitat includes:

Lagoon reefs with coral sand
Tidal flats with rocky outcrops
Outer slopes of fringing reefs (2–20 m)

Unlike A. nigricans, it tends to move more frequently in less turbulent waters.

🌡️ Temperature in the wild

The natural thermal range of Acanthurus nigricauda varies between:

24.5 °C and 28.5 °C as the optimal value
Occasional resistance to 23–30 °C in the event of environmental stress

⚠️ Temperatures above 29.5 °C can reduce the grazing rate and trigger anomalous behaviours or secondary bacterial infections, as reported by field research conducted in Papua New Guinea (Samoa Marine Studies Institute, 2018).

⚖️ Environmental parameters: the wild vs the aquarium

Parameter	In the wild	In the ideal aquarium
Temperature	24.5 – 28.5 °C	25 – 26.5 °C stable
Salinity (SG)	1.023 – 1.026	1.025 ± 0.001
pH	8.1 – 8.4	8.2 – 8.3
KH	6 – 9 dKH	8 – 10 dKH
NO₃ (nitrates)	<1 ppm on outer reefs	<5 ppm (mature reef aquarium)
PO₄ (phosphates)	<0.03 ppm	<0.05 ppm
Current	Moderate (grazing species)	Alternating medium-low movement
Lighting	High solar intensity	LED HQI or full spectrum, 200–300 µmol m²/s

📌 The most important aspect for the nigricauda is the quality of the substrate and the presence of algal biofilms, rather than pure light intensity.

🔍 Comparison with other similar Acanthurus

Species	Distinctive colour	Behaviour	Difficulty in the aquarium
A. nigricans	Dark blue with a white snout	Territorial, fast	High
A. xanthopterus	Grey-blue with yellow fins	Peaceful but very large	Very high
A. mata	Silver and black with a yellow caudal fin	Solitary, not very aggressive	Medium
A. nigricauda	Soft grey with a double black bar	Not very territorial, stable	Medium-high

A. nigricauda is often more tolerant and less subject to skin diseases than A. leucosternon or A. nigricans, but less vivid in colour.

♻️ Ethics of collection and informed purchasing

Unlike rare or protected species, A. nigricauda is not subject to CITES restrictions, but it is essential to adopt ethical criteria when selecting the supplier.

🟢 What to check before purchase:

Origin: avoid specimens from areas subject to environmental stress (e.g. post-bleaching Indonesia)
Capture technique: only hand nets, never cyanide or dynamite
Quarantine period: it must have been acclimatised for at least 2 weeks
Feeding in the shop: it must accept dry food or Nori algae

🏷️ Responsible retailers, such as AquariumClick.it, select certified importers that comply with the MAC (Marine Aquarium Council) and Sustainable Marine Trade protocols.

🏠 Keeping in the aquarium

Keeping an Acanthurus nigricauda in captivity is only possible in mature marine aquariums, with strong biological stability and a layout designed with wide swimming areas. It is an active fish, a grazer accustomed to travelling long distances in search of food, and therefore it does not tolerate confinement in narrow spaces.

⚠️ Common mistake: introducing it into aquariums that are too young, or with live rock still in the maturation phase → this entails a shortage of algal biofilm, essential in the first days of acclimatisation.

🔧 Essential requirements:

Tank start-up: at least 6 months
Oversized filtration
Refugium with macroalgae recommended
Powerful skimmer
Layout: wide swimming areas + rocks with natural algae
Cover: occasional jumper

📏 Minimum aquarium size

A tank for A. nigricauda must never be smaller than 500 net litres. Ideal for tanks from 600 to 1000 litres, especially if it is housed with other tangs.

📐 Recommended measurements:

Minimum: 150 x 60 x 60 cm
Optimal: 180 x 70 x 70 cm

👥 Minimum population in the aquarium

This is a non-gregarious species, therefore:

🧍 It must be kept singly to avoid intra-specific aggressiveness
❌ Cohabitation with other similar Acanthurus is not recommended
✅ It can live alongside surgeonfish of another genus (e.g. Ctenochaetus, Zebrasoma) in tanks of 1000L+

🧩 Compatibility with other species

The nigricauda is generally compatible with peaceful marine fish, provided they do not compete for the same space or ecological role.

✅ Good compatibility with:

Gobies (e.g. Valenciennea, Cryptocentrus)
Hawkfish (e.g. Cirrhitichthys spp.)
Pseudochromis
Gramma loreto
Anthias
Peaceful wrasses (Halichoeres, small-sized Thalassoma)

❌ Avoid:

Other Acanthurus of similar morphology
Aggressive territorial fish (Triggerfish, large Dottybacks)
Overcrowded tanks

🥬 Feeding in the wild and in the aquarium

In the wild, A. nigricauda is a detritivore/herbivore. It feeds by scraping:

Algal films
Diatoms
Epiphytic microalgae
Benthic organic detritus

In the aquarium, feeding must simulate this diet rich in vegetable fibre and silica.

🍽️ Recommended diet:

Sheets of Nori algae (unsalted) 1–2 times a day
Spirulina
Soft sinking vegetable pellets
Mix of red algae (Gelidium, Porphyra)
Rotation with chopped fresh foods: courgettes, Romaine lettuce, boiled spinach
Occasional supplements: garlic (immunostimulant), vitamins A–C–E

⚠️ Excessive use of protein feeds leads to:

Hepatomegaly (enlarged liver)
Poor intestinal absorption
Predisposition to stress-related diseases (Cryptocaryon)

💞 Reproductive behaviour

Although it is difficult to witness reproduction in captivity, in the wild A. nigricauda shows a synchronous pelagic behaviour:

Formation of small groups at sunset
Rising towards the water column for simultaneous external fertilisation
Pelagic eggs, transparent and very light

At present there are no documented successful protocols for reproduction in a private aquarium. Some research centres in Australia and Japan are studying the pelagic reproductive cycle of the species.

🐣 Protection of the fry

After fertilisation, there is no parental care at all. The eggs are entrusted to the current, and the fry develop in open water (plankton).

⚠️ No protection of the juvenile stages. High natural mortality.

🧬 Hybridisation risks

To date there are no known certain cases of hybridisation in the wild or in captivity for A. nigricauda. However, it is hypothesised that in zones of geographical overlap with A. mata or A. auranticavus, partial genetic exchanges may occur, not yet confirmed.

🛡️ Hardiness

Compared with more sensitive surgeonfish such as A. leucosternon or A. japonicus, the nigricauda is relatively hardy, but:

Susceptible to Cryptocaryon irritans if stress is high
It suffers from instability of the parameters (fluctuations in KH or NO₃)
It reacts badly to overpopulated aquariums

With good acclimatisation and feeding practices, it can live 10+ years in captivity.

💡 Lighting in the aquarium

It does not have high requirements, but:

It appreciates intense light (300–500 PAR) to favour natural algal growth
It cannot stand environments that are too dark
Ideal photoperiod: 10–12 hours a day

🌊 Current in the aquarium

Being a fish that grazes in semi-sheltered areas:

It prefers moderate current, better if oscillating
Avoid direct flows that are too strong
The use of controlled cyclic wave pumps (e.g. Vortech, Tunze) is excellent

🛒 Availability on the market

Acanthurus nigricauda is not very common on the European market, more widespread in the UK and Germany, rare in Italy.

💬 Factors to consider:

Price: medium-high (60–120 €)
Quarantine: essential before introduction
Reliable suppliers: ask for certified origin (e.g. MAC, Aquaculture Stewardship Council)

⚖️ Pros and Cons

✅ Pros:

Low aggressiveness compared to other Tangs
Elegant, understated appearance
Beneficial ecological role against algae
Relatively hardy

❌ Cons:

Not widely available in Italian shops
Not suited to small tanks
Not reproducible in the aquarium
Sensitive to swings in nitrates or salinity

Practical boxes – Acanthurus nigricauda

Box 1: Ideal parameters in the aquarium

Parameter	Recommended value
Temperature	25 – 26.5 °C
Salinity (SG)	1.025
pH	8.2 – 8.3
KH	8 – 10 dKH
NO₃ (nitrates)	< 5 ppm
PO₄ (phosphates)	< 0.05 ppm
Photoperiod	10–12 hours
Current	Moderate, alternating
Lighting	300–500 µmol m²/s PAR

Box 2: Checklist for informed purchasing

✅ Check that:

The fish is active and not apathetic
The skin is free from white spots or abrasions
The animal eats dried algae or vegetable pellets
The shop carries out preventive quarantine (min 2 weeks)
The geographical origin is specified
It is not kept with other surgeonfish in the tank

Box 3: Technical tank requirements

Minimum 500 net L
Aquarium started up for 6+ months
Layout with stable rocks and grazing areas
Powerful skimmer and refuge with macroalgae
Diversified herbivorous feeding
No other Acanthurus in the tank
Cover recommended (occasional jumps)

❓ FAQ – Frequently asked questions from the community

1. Is Acanthurus nigricauda suitable for beginners?
Yes, but only if you have a mature and spacious aquarium. It is not a fish for small or unstable tanks.

2. Can I keep it with Acanthurus leucosternon?
No, you risk strong aggressiveness. It is better to avoid several Acanthurus together, especially ones similar in shape.

3. Does it eat pest algae such as valonia or bryopsis?
No, it feeds only on algal films and microalgae. It is not an “algae-eater” for pest control.

4. What is its life expectancy?
In the wild it can exceed 10 years. In the aquarium, in good conditions, it lives 8–10 years.

5. Is it subject to diseases such as Ich?
Less than other species, but it can fall ill if stressed or malnourished.

6. Do I have to administer garlic or supplements?
Yes, garlic has an immunostimulant effect. Periodic vitamin supplements are also useful.

7. Can it live with a clownfish?
Yes, there are no problems between them, provided the space is adequate.

8. Is a refuge with macroalgae needed?
Strongly recommended, it helps with algal competition and with the balance of nutrients.

9. Is it part of the Zebrasoma family?
No, it belongs to the genus Acanthurus, still within the Acanthuridae family.

10. Can it reproduce in the aquarium?
No, to date there are no documented cases of reproduction in a home tank.

🧾 Conclusion

Acanthurus nigricauda represents a fascinating choice for experienced marine aquarists looking for a fish that is hardy, elegant and useful for the control of algal biofilm. Less showy than other surgeonfish, it stands out for its resistance, less aggressive behaviour and natural dietary needs.

Its correct management requires:

A large and mature aquarium
A herbivorous feeding regime
Stability of the parameters
Careful selection of the supplier

Introducing it into your system can bring ecological benefits, but only if you are ready to respect its biological needs. Its docile behaviour and interesting biology also make it an excellent subject of study for students and marine researchers 🧬🌿

Share questo articolo:

Testo sottoposto a revisione umana e controllo editoriale prima della pubblicazione. Responsabile editoriale Francesco Avezzano, giornalista iscritto all'Ordine dei Giornalisti della Campania. Come utilizzo l'intelligenza artificiale

Aquariology