Powder Blue Surgeonfish (Acanthurus leucosternon)

Powder Blue Surgeonfish at a glance

The Powder Blue Surgeonfish (Acanthurus leucosternon) is an unmistakable reef fish: a pale blue oval body, a dark face, a white throat and a long yellow dorsal fin, with white lower fins and a dark-edged tail. It belongs to the surgeonfish family, Acanthuridae, which also takes in the tangs and unicornfishes. This listing supplies one live fish.

The most important condition comes first. This is a fish for someone who already runs a large, established marine aquarium with steady water. It swims actively, grazes through the day and, like other tangs, can be stressed by even small amounts of ammonia or nitrite. Buy it for a system that is ready now, not one that should be ready by the time it arrives.

In the wild, FishBase describes adults on shallow, clear coastal and island coral reefs, usually on reef flats and along the upper seaward slopes, from eastern Africa to the Andaman Sea, south-west Indonesia and Christmas Island, with the range extending to Bali. They feed on benthic algae, picking at small, scattered algae and the small growths in crevices, and may be seen singly or in large feeding aggregations. That way of life explains most of what an aquarium has to provide: open water to swim through, rock to graze over and algae-rich food every day.

One fish, planned for as an adult

Each purchase supplies one Powder Blue Surgeonfish, and there is a single version of this listing. Whatever its length when it reaches you, plan the aquarium, the filtration and the rest of the stocking around the adult fish rather than the one in the bag. FishBase gives 54 cm as the maximum recorded length; that is a record rather than a promise of what every fish will reach, but it is the honest figure to plan against.

Sex is guaranteed only when the selected option explicitly states male or female. This Powderblue surgeonfish listing has no sex-guaranteed option.

Gallery images have been digitally enhanced to improve image quality. Natural colour, pattern, size and maturity can vary between live animals. Some pictures show more than one fish, and some have plants and wood in the background. You receive one fish, and those backgrounds are not a set-up guide: a powder blue needs a marine aquarium built around live or artificial rock.

Names you may see

FishBase uses the name Powderblue surgeonfish, and Wikipedia lists blue surgeonfish, powder blue tang and powder-blue surgeonfish as common names for the same species. Whichever name a shop or book uses, the scientific name Acanthurus leucosternon is the one that pins down exactly which fish is meant. FishBase also records the species as Least Concern on the IUCN Red List.

Before you choose this fish

• Is the aquarium large enough for an active fish with a recorded maximum of 54 cm, with open swimming length rather than volume alone?
• Has it carried a stable fish load long enough for ammonia and nitrite to stay at zero between tests?
• Does the current stocking include shy fish, or a tang with a similar look or body shape? Either one changes the answer.
• Can you offer algae-based foods every day, including when you are away?

If every answer is yes, a powder blue is a realistic addition towards the end of your stocking plan. If one is no, solve that first; the fish will still be worth considering once the aquarium is ready for it.

The care tab covers the aquarium, water values, feeding, arrival and health checks in the order you will need them, and the compatibility tab explains how to fit a tang into a stocking plan. If you are still weighing up a centrepiece, our marine fish collection gathers the other saltwater species we sell, each with its own care notes.

Planning the aquarium

The RSPCA's aquarium welfare guidance is blunt that no fish should be kept without a well set up and maintained filter, and the tang care sheet from OATA, the UK ornamental aquatic trade body, builds on that. Its starting rule is to buy, within reason, an aquarium as large as possible. It recommends at least 300 litres for a single individual under 20 cm and says that larger and more active species will need a larger aquarium.

A powder blue is an active swimmer, and FishBase records it at up to 54 cm. Read 300 litres as the floor for a small tang rather than a long-term home for this one. Plan a considerably larger system and favour length and open water over height, because the fish spends its day moving and grazing rather than hovering in one spot.

Why volume helps

OATA also points out that a larger aquarium gives more stability to temperature and water quality. That matters for a tang more than for many fish: waste has more water to dilute into, temperature swings are slower, and a missed test or a heavy feed has a smaller effect before you notice it.

Filtration, skimming and flow

Whatever the size, a filter is essential. For marine set-ups OATA lists live rock with sufficient water flow, an internal or external filter, or a sump-based filter, and notes that a protein skimmer can help by removing dissolved organic waste before it breaks down into more harmful substances. The RSPCA explains why the biological side matters: fish release ammonia, which is toxic; a working filter hosts beneficial bacteria that convert ammonia to nitrite, which is also toxic, and then to nitrate, which is safer. For this fish that bacterial population has to be established, and large enough for the extra waste, before it arrives.

Rockwork and swimming room

Tangs are relatively undemanding about décor, but OATA recommends live or artificial rockwork to provide cover. Build the rock into a stable structure that leaves long, clear swimming lanes along the front and through the middle of the tank, rather than filling the aquarium from end to end. The rock surfaces also grow algae films the fish can graze between meals, which suits a species that picks at small growths in crevices in the wild.

Where it fits in a new system

If you are building an aquarium with a powder blue in mind, think in stages. First the system runs and matures until its filter bacteria are established. Then the other residents go in a few at a time: OATA explains that the beneficial bacteria need to increase every time more fish are added and feeding increases, and that overstocking or stocking too quickly can cause new tank syndrome, with unhealthy levels of ammonia and nitrite. Only when the aquarium has carried that fish load steadily does the tang go in, towards the end of the plan.

Size the filtration and skimming for the finished stocking list, including a large adult powder blue, rather than for the fish already in the tank. It is far easier to build that capacity in at the start than to add it once the tank is full.

Water values and routine care

OATA's care sheet for tangs and rabbitfish describes these fish as usually undemanding of water chemistry and gives the values below as a general guide for the group, not a species-specific optimum. It adds that a reef aquarium may need some values altered to suit more sensitive species. For a powder blue, the priority is consistency: values that stay where you set them, and ammonia and nitrite that never register.

FishBase gives 23–28°C for the species' wild reef environment. That is a record of where it lives rather than an aquarium target. In the tank, hold the temperature steady inside the 24–26°C guidance instead of letting it wander towards either end of the wild range.

What the numbers are for

• Salinity: evaporation removes water but leaves the salt behind, so salinity creeps up between water changes unless evaporated water is replaced with fresh water. Measure it the same way each time.
• Carbonate hardness: this is the buffer that holds pH steady, which is why OATA gives a range for it alongside pH.
• Calcium and magnesium: OATA includes both in its guidance; they matter most where corals and other reef animals share the aquarium.
• Nitrate: less toxic than ammonia or nitrite, but OATA puts a ceiling of 50 mg per litre on it, and regular partial water changes are the main way to hold it down.

Tests worth owning

Because the whole plan rests on steady values, keep your own test kits rather than relying on occasional checks elsewhere. For a powder blue that means ammonia, nitrite, nitrate, pH and carbonate hardness, a reliable way to read salinity, and a thermometer you look at every day. Add calcium and magnesium tests if corals share the aquarium.

A weekly routine that suits a tang

OATA strongly recommends a partial water change of 25% at least once every week, using a siphon to lift solid waste from the substrate. Match the new salt water to the aquarium's salinity and temperature before it goes in, so the change itself does not become a swing.

• Test ammonia, nitrite and nitrate regularly; OATA's ceiling for nitrate is 50 mg per litre, and ammonia and nitrite should read zero.
• Check filters regularly so they do not block.
• If filter media needs cleaning, rinse it lightly in the tank water removed during the water change, not under the tap: chlorine or chloramine in tap water can kill the beneficial bacteria living in the media.
• Clean the protein skimmer regularly so it keeps removing waste efficiently.
• Note your results so a slow drift in any value is easy to spot.

OATA's reason for this discipline is plain: tangs and rabbitfish can be stressed by even the smallest amounts of ammonia and nitrite, and that stress may then cause them to develop various diseases. Good husbandry is not an extra for this fish; it is most of the care.

When something reads wrong

If a test shows ammonia or nitrite, find the cause before adding anything: a recent new fish, heavier feeding, a blocked or over-cleaned filter, or food left to rot behind the rock. OATA links the classic new tank syndrome to adding fish faster than the filter bacteria can grow, which is why this fish belongs in an aquarium that has already carried a stable fish load for some time.

Feeding an algae grazer

FishBase describes adult powder blues feeding on benthic algae, taking small, sparsely scattered algae and small growths in crevices. OATA's feeding advice for the group follows the same pattern: tangs and rabbitfish are mainly herbivores, and their diet should reflect that with foods high in algae. OATA is also clear about the risk: if enough algal food is not provided, they may become ill.

What to offer

• Nori (dried seaweed) sheets, which the fish can graze over time
• Algae-based flake
• Grazing tablets
• Small meaty frozen foods such as mysis shrimp, enriched brine shrimp or krill, as a smaller part of the diet

How much and how often

OATA's guideline for tangs is to feed only what they can eat within a few minutes, twice a day. Algae sheets and grazing tablets are the exception: they need a longer time in the aquarium because the fish graze on them rather than snapping them up. Take out anything left once the fish has lost interest, because uneaten food breaks down and releases toxic waste into the water.

A practical day might combine an algae-based flake portion at each of the two feeds with a nori sheet or grazing tablet left in for the fish to work at, and a small portion of frozen mysis or brine shrimp as part of one feed. Keep the algae share clearly larger than the meaty share.

Variety within the algae foods

Rotating between nori, algae-based flake and grazing tablets gives the fish variety without moving away from the algae-rich base OATA recommends. Keep the meaty frozen foods as the smaller share, and change one food at a time so you can see how it is taken.

Algae on the rock is a bonus, not the diet

In an established aquarium a powder blue will graze the films that grow on rock and glass, which suits its natural habit of picking at small growths. It is not a substitute for prepared food. OATA's warning that tangs may become ill without enough algal food applies even in a tank that looks green, because you cannot easily tell how much the fish is getting from the rock alone.

Watching condition

OATA lists an increase or decrease in body weight and condition, and reduced intake or lack of interest in food, among the changes worth acting on. Look at the powder blue's outline from the side each week. A fish that looks thinner, or that starts ignoring food it used to take, needs a water test first and then a closer look at how much algae it is actually eating. Overfeeding is the opposite risk: extra food raises waste, and waste is what this fish tolerates least.

Feeding in a shared tank

Tangs are active fish, so in a mixed aquarium make sure slower tank mates still get their share, and spread foods so one fish cannot hold the only feeding spot. Grazing foods left in for longer give the powder blue something to work on without the whole ration going in at once.

Delivery, acclimatisation and the first weeks

Every order is hand-packed by our team. The fish is hand-bagged in pure oxygen and packed in an insulated poly box, with a heat pack when the weather calls for it. A licensed live-animal courier carries the tracked parcel, and we email the tracking number with your confirmed delivery date so you know when to be in. The full terms are on our delivery and Live Arrival Guarantee page.

The day before

• Test the aquarium: ammonia and nitrite should read zero before any new fish goes in.
• Check that the heater, salinity and temperature are stable and where you want them.
• Keep the tracking email and your order number to hand, and make sure your phone can record a continuous video.
• Plan to be at home for the delivery.

On the day it arrives

1. Make sure someone is at the delivery address to receive the parcel; live fish cannot be left unattended.
2. Before the box is opened, start a continuous unboxing video with the parcel still sealed and the outer box in view, and keep filming in one take until the fish can be seen inside the sealed bag.
3. Open and inspect the parcel the same day it arrives.
4. Float the sealed bag in the aquarium for 20–30 minutes to acclimatise the fish slowly.
5. Release the fish without pouring the bag water into the aquarium.

If anything has gone wrong, contact us the same day, WhatsApp being fastest, with your order number and the unboxing video, and we will arrange a replacement or refund. The Live Arrival Guarantee depends on that video showing the parcel still sealed, then opened, then the fish still in its bag.

The first weeks

OATA describes a healthy fish as having clear bright eyes, undamaged fins, intact scales, no ulcerations or bumps and appropriate swimming behaviour. Use that as your reference in the days after release, and compare what you see each day with the day before.

Keep feeding modest at first and test the water more often than usual. OATA explains that the filter's bacteria need to increase every time more fish are added and feeding increases, so a new powder blue adds load that the filter has to catch up with. That is also why no other new fish should follow it in quickly: build the stocking slowly and let each addition settle.

Give the fish time to find its way around the rockwork and open water, offer algae-based food from the first days, and remove anything it leaves.

Handling and health checks

Handling with care

OATA warns that tangs have sharp, modified scales near the tail that resemble a scalpel and can injure people, and that some species may have venom glands at their base. Take care whenever you catch, move or work around a powder blue: move it gently, avoid handling it bare-handed and keep your fingers clear of the base of the tail during maintenance.

Signs worth acting on

All fish vary a little in behaviour and appearance, but OATA lists changes that help identify a problem before it becomes a real health issue:

• Swimming: hanging at the surface, sitting on the bottom or swimming erratically
• Colour: turning darker or paler than normal
• Temperament: more aggression, or more hiding, than usual
• Breathing: gill covers moving slower or faster than normal
• Appearance: white spots or fluffy growths, or loss of fins or scales
• Condition: a gain or loss in body weight
• Feeding: reduced intake or lack of interest in food

If you are concerned, OATA's advice is to test your water quality first and then speak to your retailer. With a tang, water is the first suspect because of how strongly it reacts to ammonia and nitrite. We are happy to talk through test results and what has changed in the aquarium.

A daily look at feeding time

Feeding time is the easiest moment to run through that list without disturbing the fish. Watch the powder blue come out to feed and check its swimming, eyes, fins and breathing while it eats. If it hangs back, breathes quickly, shows white spots or has lost interest in food, test the water that day rather than waiting for the weekly routine, and keep a note of what you saw so any change is easier to describe.

Keeping stress low

Most of what keeps a powder blue healthy has already appeared above: a large, mature aquarium, stable values, enough algae in the diet, a stocking plan that does not pit it against look-alike tangs, and patience when adding fish. None of these is complicated on its own. The challenge is keeping all of them in place every week for a fish that OATA notes can live for many years in a well-matured set-up with good water quality.

Tank mates and stocking order

OATA's compatibility advice for tangs and rabbitfish comes down to three points:

• Tangs and rabbitfish can be mixed, provided they do not look too similar.
• They are active fish and should not be mixed with shy species.
• Tangs with similar body shapes should be added at the same time and towards the end of stocking an aquarium, because they can be territorial and may bully any new additions.

OATA also advises checking with your retailer before adding any tang or rabbitfish, so that it will mix with the fish you already keep.

What that means for a powder blue

Plan on a single powder blue. A second fish of the same species looks exactly like the first, so it fails OATA's look-alike test. If you want another tang as well, choose one with a clearly different shape and colour; if you do intend to keep two tangs of similar shape, OATA's advice is to add them together, late in stocking, rather than one after the other.

The powder blue itself should also go in towards the end of stocking. Adding it last means the filter is established, most other residents are settled, and the tang arrives into a tank where it is the newcomer rather than the resident defending space against each later addition.

Three common situations

• An established aquarium with damsels or a marine angelfish and no other tang: the powder blue can be planned as the last addition, provided the tank is large enough for it.
• An aquarium that already holds a tang of similar shape: do not add a powder blue later. OATA's advice is that similar-shaped tangs go in together, not one after the other.
• An aquarium built around shy fish: choose a different centrepiece, because tangs are active and OATA advises against mixing them with shy species.

OATA's wording covers both appearance and body shape, so judge a possible second tang on outline as well as colour.

Reef aquariums

FishBase records the powder blue's wild food as benthic algae. If the aquarium is a reef system, OATA notes that some of the water values in the care tab may need to be altered to accommodate more sensitive species, so set the water for the most demanding inhabitant and keep it steady. How any tang behaves around a particular invertebrate or coral also depends on the individual fish and the rest of the tank, so watch closely after introduction.

Building the stocking list

Work out the full list before the powder blue goes in. Put the other residents in first and let them settle, with the tang near the end. Keep an eye on the first days after each addition, especially at feeding time, and be ready to move a fish if one is being chased repeatedly. A large aquarium with open water and plenty of rock gives every fish more room to keep out of each other's way.

Questions keepers ask

How big does a Powder Blue Surgeonfish get?

FishBase records a maximum total length of 54 cm. That is the largest length on record and individual fish vary, but it means the fish should be bought for an aquarium that can hold a large, active adult, whatever its length on arrival.

What size aquarium does it need?

OATA's sheet for tangs recommends at least 300 litres for a single individual under 20 cm and says larger, more active species need more. A Powder Blue Surgeonfish is an active swimmer that can grow well beyond 20 cm, so treat 300 litres as a starting point it will outgrow and plan a considerably larger, long aquarium with open swimming space.

Can I keep more than one together?

Plan on one. OATA advises mixing tangs only when they do not look too similar, so a second powder blue is a poor match. If you want another tang as well, choose one with a clearly different shape and colour, and stock it towards the end of the plan.

Is a Powder Blue Surgeonfish suitable for beginners?

It suits keepers who already run a large, established marine aquarium with steady water. OATA notes that tangs can be stressed by even the smallest amounts of ammonia and nitrite, which may then lead to disease, so it is a poor choice for a new marine tank or a first saltwater fish.

What does it eat?

Mainly algae. In the wild it grazes small, scattered algae and growths in rock crevices. In the aquarium, build the diet around nori sheets, algae-based flake and grazing tablets, add small frozen foods such as mysis or enriched brine shrimp, and feed what it can eat within a few minutes twice a day, leaving nori or grazing tablets in for longer.

What temperature and pH does Acanthurus leucosternon need?

OATA's group guidance for tangs and rabbitfish gives 24–26°C, pH 7.9–8.3, salinity 1.020–1.025 and carbonate hardness of 8–12 dKH, with ammonia and nitrite at zero. FishBase records its wild reef habitat at 23–28°C; in the aquarium, keep the temperature steady within the OATA range.

Is it aggressive towards other fish?

Tangs can be territorial. OATA notes that tangs with similar body shapes may bully any new additions, which is why this fish should go in towards the end of stocking and why a look-alike tang should not be added after it has settled.

Which fish can live with a Powder Blue Surgeonfish?

OATA names angelfish, damsels and some butterflyfish as good tank mates for tangs, and advises against shy species because tangs are active. Choose active companions that differ clearly in shape from it, and plan the whole stocking list before it goes in.

How does a Powder Blue Surgeonfish arrive alive in the UK?

It is hand-bagged in pure oxygen and packed in an insulated poly box, with a heat pack when the weather calls for it, then carried by a licensed live-animal courier. Someone must be in to receive it. For the Live Arrival Guarantee, film a continuous unboxing video from the sealed parcel, open it the same day, float the bag for 20–30 minutes and never pour the bag water into the aquarium.

Sources and further reading

These are the public sources behind the care and natural-history notes above, with what each one covers.

• FishBase: Acanthurus leucosternon – identity, family, distribution, wild habitat, natural diet and maximum recorded length.
• Wikipedia: Acanthurus leucosternon – common names and a general natural-history summary.
• OATA: How to look after tangs and rabbitfish – group-level water values, aquarium size, feeding, maintenance, handling and compatibility for tangs and rabbitfish.
• RSPCA: fish environment – general aquarium welfare, filtration and the nitrogen cycle.
• Tropical Fish Co delivery and Live Arrival Guarantee page – packing, courier, acclimatisation and claims, linked in the arrival section of the care tab.