Palette surgeonfish (Paracanthurus hepatus)

Recognise a reef-associated surgeonfish

The Palette surgeonfish, Paracanthurus hepatus, is a marine member of the surgeonfish family Acanthuridae. It is also called the regal tang in OATA guidance. Its blue body, broad black marking and yellow tail give it a distinctive appearance, while the sharp modified scale near the tail demands careful handling.

FishBase records this species from clear, current-swept terraces on seaward reefs across the Indo-Pacific. Fish may swim in loose aggregations one or two metres above the bottom. Juveniles and subadults have been observed gathering near isolated coral heads and hiding tightly among the branches when alarmed. These observations explain the need for both open swimming room and accessible cover in an aquarium.

Wild fish feed on zooplankton and occasionally on algae. Aquarium feeding should preserve that variety while following the algae-focused tang routine set out below. This is not a fish to choose on colour alone: the decisive questions are whether the aquarium can support an active fish approaching the recorded maximum length, whether the filter is mature, and whether existing fish can live with an active tang.

The natural-history summary for Paracanthurus describes P. hepatus as an Indo-Pacific surgeonfish and the only member of its genus. Plan for this exact species rather than applying the requirements of a smaller tang.

Choose the dispatch size deliberately

One purchase supplies one animal of the selected option. The selector uses the labels “4 - 5,9 cm”, “6 - 9 cm” and “>9 cm”; use the live size selector to see the choices shown when you order. The size you select is the size supplied, not the adult size.

A smaller dispatch measurement does not reduce the long-term space requirement. Compare the chosen size with the 20 cm threshold used in OATA’s aquarium-volume guidance, then plan for FishBase’s recorded maximum of 31 cm total length. If the aquarium only suits a fish while it remains below 20 cm, it is not the finished long-term plan.

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

Some gallery images are representative, based on reference photographs of this species, and none shows the exact animal supplied, so colours can look slightly different from the live animal.

Choose the size by checking three things together: the aquarium’s present capacity, its ability to accommodate future growth, and the behaviour of its established residents. Dispatch size helps you plan introduction and immediate space; adult length controls the lasting decision.

Check the decisive numbers first

OATA’s tang and rabbitfish guidance gives group-level aquarium targets rather than a species-specific optimum: at least 300 litres for one individual under 20 cm, with a larger aquarium for larger or more active fish. Its routine water range is 24–26°C, salinity 1.020–1.025 and pH 7.9–8.3.

Treat 31 cm as a recorded maximum for planning, not a promise that every individual will reach exactly that measurement. The volume figure has a clear limit: it applies to one fish under 20 cm. A Palette surgeonfish approaching or exceeding that threshold needs a larger aquarium selected around its adult length, activity and the space occupied by rockwork and other fish.

A suitable keeper can maintain all these water values together, complete weekly maintenance and make a cautious compatibility assessment before introduction. The aquarium should already be mature and filtered rather than relying on a future upgrade to correct an immediate shortfall.

Build space around growth and movement

Start with the adult plan. FishBase gives 31 cm total length as the recorded maximum, while OATA recommends at least 300 litres only for a single individual under 20 cm. Use the larger-fish requirement to judge the permanent aquarium rather than treating 300 litres as a lifetime figure.

Balance cover with swimming room

Provide live or artificial rockwork for cover, but retain clear water around it for an active fish. In nature this species swims above current-swept reef terraces and retreats among coral branches when alarmed. An aquarium layout should therefore offer a direct choice between open movement and shelter instead of filling the entire interior with dense décor.

When comparing two layouts of the same volume, favour the one that leaves useful swimming space after rockwork, filters and other equipment are installed. Nominal litres alone do not show how much usable room remains. A larger aquarium also gives greater stability in temperature and water quality, which matters for a tang that can be stressed by even small amounts of ammonia or nitrite.

Use the 20 cm threshold as a checkpoint

• Below 20 cm: keep one individual in at least 300 litres and assess whether its present activity is comfortably accommodated.
• Approaching 20 cm: move to the larger long-term plan before space becomes restrictive.
• Planning from the start: allow for a fish that may approach 31 cm total length and for the volume displaced by rockwork.

Do not use a small dispatch option as a reason to postpone this decision. The aquarium must meet the fish’s needs on arrival and remain appropriate as it grows. If several large or active fish share the system, assess their combined use of swimming room before adding another.

Hold the water inside one stable range

Run the aquarium at 24–26°C, salinity 1.020–1.025 and pH 7.9–8.3. Check these values as a set: a temperature inside range does not compensate for detectable ammonia, unsuitable salinity or pH outside the recommended interval.

Ammonia and nitrite require particular attention because tangs may become stressed by even small amounts. If either is detectable, stop treating the aquarium as ready for another fish. Test the water, check filtration and correct the waste-processing problem before increasing stocking or feeding.

Nitrate has an upper limit rather than a preferred endpoint: it must not exceed 50 mg per litre. Weekly partial water changes, controlled feeding and maintenance of the filter and protein skimmer help prevent waste from accumulating. A reef aquarium may require different targets to meet the needs of more sensitive inhabitants, so establish a shared operating range before combining this fish with them.

Use consistent measurements to distinguish a water problem from a behavioural change. If the fish becomes unusually pale, dark, withdrawn, erratic or uninterested in food, test ammonia, nitrite, nitrate and the core marine values rather than judging water quality by appearance alone.

Mature the filter before adding the fish

A working filter is essential. RSPCA aquarium welfare guidance explains that fish release toxic ammonia, which beneficial bacteria convert first to toxic nitrite and then to the safer nitrate. The aquarium must have an established biological filter capable of processing the waste created by its existing population and the new fish.

Choose a complete filtration route

A marine system may use live rock with sufficient water flow, an internal or external filter, or sump-based filtration. A protein skimmer can be added to remove dissolved organic waste before it breaks down into more harmful substances. Whichever route you use, keep it accessible enough to inspect and maintain without allowing blockages to build up.

Increase the fish population slowly. Each addition and each rise in feeding requires the established bacterial population to process more waste. Adding too many fish too quickly can cause new tank syndrome because the available nitrifying bacteria cannot cope with the increased ammonia load.

Confirm readiness before introduction

• Check that ammonia is zero mg per litre.
• Check that nitrite is zero mg per litre.
• Confirm that nitrate does not exceed 50 mg per litre.
• Verify temperature, salinity and pH before opening space for another fish.
• Check filters for obstruction and confirm that maintained equipment is operating normally.

A mature aquarium is one in which the biological filtration is already functioning; waiting for the fish to arrive before solving filtration problems puts the animal into the unstable stage. Good water quality, adequate volume and gradual stocking work together. None replaces the others.

Complete the weekly maintenance routine

Change 25% of the aquarium water at least once every week. Use a siphon to remove solid waste from the substrate where practical, and use the maintenance session to check filters and the protein skimmer for reduced performance or blockages.

Protect the biological filter

If filter media needs cleaning, rinse it lightly in aquarium water removed during the partial water change. Do not run established biological media under the tap: chlorine or chloramine may kill the beneficial bacteria responsible for converting ammonia and nitrite. The aim is to remove obstructing debris without stripping away the working bacterial population.

1. Test ammonia, nitrite and nitrate and note whether each result meets the required limit.
2. Prepare the 25% partial water change and siphon out accumulated solid waste.
3. Use removed aquarium water for any light rinsing of filter media.
4. Check filters for blockages and restore their normal operation after cleaning.
5. Clean the protein skimmer regularly so it can continue removing dissolved organic waste.
6. Recheck temperature, salinity and pH as part of the aquarium’s routine monitoring.

Match maintenance to what you observe. Uneaten food increases the waste entering the system, while a blocked filter or poorly maintained skimmer reduces the system’s ability to deal with it. Correct the cause rather than relying only on a larger water change after a problem appears.

The weekly change is a minimum frequency, not permission to let nitrate rise to 50 mg per litre between sessions. Keep nitrate below that maximum through feeding control, filtration and water changes. Test promptly whenever swimming, colour, breathing, hiding or feeding changes, because water-quality problems may show first through the fish’s behaviour or appearance.

Feed for grazing and wild diet

Feed twice a day, offering only what the fish can eat within a few minutes. Build the aquarium routine around algae-rich foods such as nori sheets, algae-based flake and grazing tabs, then include small meaty frozen foods such as mysis shrimp, enriched brine shrimp or krill.

This combination reflects two useful parts of the fish’s biology. FishBase describes wild Palette surgeonfish feeding on zooplankton and occasionally on algae, while OATA’s aquarium routine for tangs and rabbitfish emphasises enough algae-based food to maintain condition. Do not reduce the diet to only one of those elements.

Use a simple two-feed routine

Judge quantity by direct observation. If loose food remains after a few minutes, the portion was too large. Nori sheets and grazing tabs are the exception to that short window because they are intended to remain accessible while the fish grazes.

Overfeeding creates a second care problem: uneaten food breaks down and releases waste into the water. A larger portion is not a substitute for dietary variety, and a powerful filter is not a reason to ignore leftovers. Keep both daily feeds controlled, maintain the algae component and monitor body condition and interest in food.

Acclimatise without rushing the filter

Prepare before the delivery window. Make sure someone can receive the parcel, confirm that the aquarium is mature, and test ammonia and nitrite at zero mg per litre. Check temperature, salinity and pH against the operating ranges before the bag is opened.

Follow the store’s delivery, acclimatisation and Live Arrival Guarantee policy. Float the closed bag for 20–30 minutes before releasing the fish, and never pour the bag water into the aquarium.

Use this arrival sequence

1. Be present to receive the live-animal parcel rather than leaving it unattended.
2. Inspect the fish’s breathing, posture and general condition while it remains contained.
3. Float the bag for 20–30 minutes.
4. Release the fish without adding the bag water to the aquarium.
5. Observe swimming, breathing, colour and hiding behaviour after introduction.
6. Test the aquarium promptly if behaviour or appearance changes.

Acclimatisation cannot compensate for an immature filter or unsuitable water. Adding the fish also increases the waste and feeding load, so avoid adding several unrelated fish in quick succession. Similar-shaped tangs require separate compatibility planning because OATA advises introducing them simultaneously and towards the end of stocking, but that does not remove the need for adequate biological capacity.

Use the first observations as a baseline. Note how the fish swims, breathes, hides and responds to food so later changes are easier to recognise. Focus on the animal and water values rather than trying to diagnose a condition from colour alone.

Respond to health changes with water tests

A healthy fish should have clear, bright eyes, undamaged fins, intact scales, no ulcerations or bumps, appropriate swimming behaviour and a normal interest in food. Look for changes each day and during both feeds, when differences in appetite, breathing and movement are easiest to compare.

Match each warning sign to an action

Wild juveniles and subadults hide among coral branches when alarmed, so hiding should be assessed alongside breathing, colour, feeding and the behaviour of tank mates. A sudden increase in hiding still deserves attention, particularly when an active or territorial fish has recently been introduced.

If you are concerned about any health change, test the water quality and contact us for further guidance. This step identifies whether ammonia, nitrite, nitrate, temperature, salinity or pH is contributing to the problem without guessing from one visible sign.

Keep treatment decisions outside routine observation. The immediate priorities are accurate water results, maintained filtration, a clear account of the change and prompt guidance appropriate to the condition.

Protect the fish and yourself during care

Tangs have sharp modified scales near the tail that resemble a scalpel and can injure people. FishBase also identifies an anterolateral glandular groove with a venom gland in Paracanthurus hepatus. Minimise handling and keep hands away from the tail area whenever work brings you close to the fish.

Arrange routine maintenance so the fish can move into cover while you siphon waste or service equipment. Rockwork gives it a retreat, but leave enough open space for normal swimming. Watch the fish’s position before moving equipment or placing a hand into the aquarium.

Plan each growth checkpoint before it arrives

• Compare the fish’s increasing length with the under-20 cm limit attached to the 300-litre recommendation.
• Review how much swimming room remains after rockwork and other fish are accounted for.
• Check whether established tank mates are becoming more withdrawn or whether territorial behaviour is increasing.
• Keep the weekly 25% water-change routine and twice-daily feeding proportionate to what the fish actually consumes.

OATA notes that tangs can live for many years in a well-matured aquarium with good water quality. Treat the purchase as a long-term space and maintenance commitment without assigning a fixed lifespan. The recorded 31 cm maximum, active behaviour and need for stable water are more useful planning tools than the dispatch measurement alone.

Reassess before the fish reaches a space limit, not after. An aquarium that was adequate for a fish under 20 cm may cease to be the right long-term environment as the animal grows or as other large fish are added.

Screen every tank mate before purchase

Choose tank mates by activity, adult space and resemblance rather than by a general “community fish” label. OATA advises that active tangs and rabbitfish should not be mixed with shy species. It also says tangs and rabbitfish can be mixed when they do not look too similar.

When using the marine fish collection to compare a possible addition, identify the exact species first. Then check whether it is shy, resembles the tang in body shape, or would make the aquarium too crowded when all residents reach adult size.

Compatibility remains an individual assessment because fish can vary in behaviour and temperament. OATA lists angelfish, damsels and some butterflyfish as examples of tank mates, but those group examples do not override aquarium size, the behaviour of the individual fish or the requirements of the exact species being considered.

Ask us for one stocking and compatibility assessment before combining this tang with an established community. Include the aquarium volume, the Palette surgeonfish’s selected size, the names and sizes of current residents, and the order in which fish were introduced.

Plan additional tangs as one stocking decision

Plan this purchase as one fish. Although wild Palette surgeonfish have been observed in loose aggregations and juveniles may gather near isolated coral heads, that natural behaviour is not a direction to place several tangs into an aquarium without a complete adult-space and compatibility assessment.

Similar-shaped tangs may become territorial and bully new additions. OATA advises adding such tangs simultaneously and towards the end of stocking the aquarium. Make that decision before either fish enters the system; adding a lookalike later is the pattern most directly associated with the territorial warning.

Check the plan in the right order

1. Confirm that the aquarium exceeds the at-least-300-litre figure as required for the size and activity of every planned tang.
2. Allow for the Palette surgeonfish’s recorded maximum of 31 cm total length.
3. Compare body shape and appearance, avoiding tangs or rabbitfish that look too similar.
4. Exclude shy species from the plan.
5. Confirm that the mature filter can handle the increased waste and feeding load.
6. If similar-shaped tangs remain in the plan, introduce them simultaneously and towards the end of stocking.

Simultaneous introduction is not permission to overstock or rush an immature filter. OATA’s wider introduction advice still requires fish numbers to increase slowly so beneficial bacteria can adjust to the added waste. Resolve that tension by designing the whole stocking sequence in advance rather than adding fish opportunistically.

After introduction, watch for increased aggression, persistent hiding, changed colour, abnormal swimming or reduced feeding. These signs can indicate a compatibility or water-quality problem, so test the water and reassess the interaction rather than assuming territorial behaviour will settle by itself.

Answer the main buying questions

What is Paracanthurus hepatus?

It is the Palette surgeonfish, the only species in its genus and an Indo-Pacific, reef-associated member of the surgeonfish family Acanthuridae.

How is the Palette surgeonfish sold?

One purchase supplies one animal of the selected size option. Check the live selector for the size choices shown when ordering.

Which size should I choose?

The selector uses “4 - 5,9 cm”, “6 - 9 cm” and “>9 cm” as dispatch measurements. Choose for the aquarium on arrival, then plan independently around the recorded maximum of 31 cm total length.

What aquarium does Paracanthurus hepatus need?

Use at least 300 litres for one fish under 20 cm, then choose a larger aquarium for a larger or more active fish. Provide rockwork for cover, clear swimming room and mature filtration.

Should it be kept alone or in a group?

Plan this purchase as one fish. Wild fish form loose aggregations, but aquarium tangs that look alike may become territorial; only plan additional tangs after assessing adult space, appearance and introduction order.

What water parameters suit the Palette surgeonfish?

Maintain 24–26°C, salinity 1.020–1.025 and pH 7.9–8.3, with ammonia and nitrite at zero mg per litre and nitrate not exceeding 50 mg per litre. These are OATA’s group-level aquarium values for tangs and rabbitfish, not a species-specific optimum.

What should I feed Paracanthurus hepatus?

Feed twice daily with enough algae-rich food, including nori, algae-based flake or grazing tabs, plus small meaty frozen foods such as mysis, enriched brine shrimp or krill. Loose food should be eaten within a few minutes.

How do I acclimatise it?

Start filming before opening the sealed parcel and continue in one take through opening to the fish still inside the sealed bag. Then float the bag for 20–30 minutes before releasing the fish, and never pour the bag water into the aquarium.

Which tank mates can live with this fish?

Avoid shy species and tangs or rabbitfish that look too similar. Screen every candidate by adult space, activity, body shape and individual behaviour; similar-shaped tangs require simultaneous introduction towards the end of stocking.

Care and identity references

• FishBase: Paracanthurus hepatus — scientific identity, family, distribution, maximum recorded length and wild biology.
• Wikipedia: Paracanthurus — genus placement and concise Indo-Pacific natural history.
• OATA: How to look after tangs and rabbitfish — aquarium water, feeding, maintenance, introduction and compatibility guidance.
• RSPCA aquarium environment guidance — biological filtration and the aquarium nitrogen cycle.