Bicolour parrotfish (Bolbometopon bicolor)

Meet a large Red Sea algae grazer

The Bicolour parrotfish is a marine, reef-associated member of the Scaridae family. FishBase records it from depths of 1–30 metres and describes the wild fish as a benthic grazer of algae. FishBase now lists it as Cetoscarus bicolor.

Its distribution is unusually focused. A natural-history summary for the species identifies it as endemic to the Red Sea rather than broadly distributed across the whole Indo-Pacific. That identity matters when planning care: this is a tropical marine fish whose aquarium must be prepared around a large adult, stable saltwater conditions and access to algae-based feeding.

What its natural behaviour means in an aquarium

“Benthic grazer” means that it feeds from surfaces around the bottom and structure of its habitat rather than taking all of its food from open water. Build the feeding plan around algae that can be presented for grazing, then watch whether the fish actively feeds and maintains its body condition. Its wild feeding mode does not by itself settle whether a particular coral, rock arrangement or mobile invertebrate will be compatible.

The recorded depth and tropical range describe the wild environment; they are not aquarium dimensions or stocking limits. For home care, use the operating targets and maintenance decisions below. The defining planning fact is the recorded adult length: this is not a small parrotfish that can be matched to a standard community marine aquarium.

Plan the aquarium around 50 cm standard length

FishBase records a maximum of 50 cm standard length for male or unsexed fish. Use 50 cm as the firm planning reference rather than treating it as the total space occupied by a swimming fish. Aquarium dimensions must allow an adult to turn, move past the aquascape and reach feeding areas without being channelled through narrow gaps.

OATA’s wrasse guidance is broad group advice rather than a parrotfish volume rule. It recommends at least 150 litres only for an individual of the smaller species and explicitly says species over 15 cm need a larger aquarium. At a recorded 50 cm, this fish is far beyond that smaller-species benchmark. Do not use 150 litres as its minimum.

Use a dimension-led space check

• Adult turning room: map a 50 cm standard-length body against the clear front-to-back width, allowing further room for the tail and turning arc.
• Clear movement: arrange structure so the fish can move around it rather than becoming trapped between rockwork and glass.
• Grazing access: keep useful feeding surfaces reachable without filling every route with décor.
• Waste capacity: size biological filtration for the completed stocking plan, not just the fish at introduction.
• Future residents: leave additional room when other fish share the system; OATA notes that mixed-species aquariums need to be larger.

Aquarium volume still matters because larger water volumes generally change more slowly, but litres alone can hide unsuitable proportions. A tall, narrow system and a long, deep system may hold similar volumes while offering very different turning room. Start with the 50 cm adult reference, test the usable dimensions, then assess filtration and the needs of every intended resident.

Understand the animal and purchase unit

One purchase supplies one animal. Keep the 50 cm standard-length maximum central to the aquarium plan rather than treating the animal’s size on arrival as a limit on future growth.

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

Some gallery images have been digitally enhanced to improve image quality. They show the listed type of animal rather than guaranteeing the exact markings of the individual supplied, so natural colour and pattern can vary.

Decide whether this fish fits your plan

Choose it only after the adult-space calculation, biological filtration and compatibility screening have been completed. The routine water target used here is 24–26°C, within FishBase’s recorded wild temperature range of 24–28°C. Ammonia and nitrite must remain at zero, and the aquarium should be mature before another fish is added to its biological load.

The fish suits a deliberately planned marine system centred on a large algae grazer. It should not be selected merely from its size on arrival or gallery appearance. If the adult calculation points to a smaller marine animal, browse the current marine fish collection and compare adult sizes, feeding biology and compatibility requirements before choosing.

Check whether this animal suits the aquarium

Hold marine water within clear operating limits

For routine aquarium management, use 24–26°C. FishBase records 24–28°C for the species in the wild, while OATA’s broad wrasse guidance narrows the aquarium operating range to 24–26°C. The narrower target stays inside the species-level environmental range rather than widening it.

Test before introduction so the decision is based on measured water rather than the appearance of a clear aquarium. Temperature within 24–26°C is only one checkpoint: a system with detectable ammonia or nitrite is not ready for another fish. Check salinity and pH alongside the nitrogen compounds because all of these values form the operating environment.

Respond to a reading, not a guess

• If ammonia or nitrite is detectable, pause the introduction and restore the biological filter’s ability to process waste.
• If nitrate reaches 50 mg per litre, bring it below that maximum through the established maintenance routine.
• If temperature is outside 24–26°C, identify the cause and return the system to the operating range before introduction.
• If pH or salinity is outside its range, stabilise the aquarium before adding another biological load.

Use repeated readings to distinguish a stable result from a brief snapshot. For example, a single zero-ammonia reading does not cancel a later detectable result after feeding or maintenance. Record the value, time and any recent change, then retest while correcting the cause. This creates a practical baseline for judging whether the aquarium remains steady as the fish settles and its feeding load becomes part of the system.

Reef aquariums may need different limits for more sensitive residents. In that case, compare every intended value with the requirements of those residents and use an overlap that remains within 24–28°C for this fish.

Choose usable space rather than litres alone

Begin the layout with the recorded 50 cm standard length drawn to scale. Add room beyond that line for the tail, turning movement and clearance from rockwork. This simple exercise prevents a large total volume from disguising a front-to-back dimension that is too tight for an adult.

Work through the layout in order

1. Mark the adult reference. Place a 50 cm marker against the proposed clear swimming area.
2. Check the narrowest point. Include rock projections, pumps and internal filter housings when judging usable width.
3. Trace more than one route. The fish should not depend on a single corridor between fixed structures.
4. Keep feeding surfaces reachable. Its algae-grazing biology makes access to surfaces part of the feeding plan.
5. Recalculate for tank mates. Each additional fish increases both space use and the load handled by beneficial bacteria.

Securely arranged structure should leave open routes rather than a dense wall. The aim is not a bare display or a prescribed aquascape style; it is a layout that accommodates the adult reference while allowing maintenance access. If a siphon cannot reach an area where waste accumulates, redesign that area before the fish is introduced.

Apply the same discipline to equipment placement. A pump guard, intake, heater or return can reduce the clear space even when it occupies little nominal volume. View the aquarium from above as well as from the front, because turning room depends heavily on depth.

Test the proposed routes during routine maintenance rather than judging them only when the aquascape is new. If equipment cleaning requires blocking the main passage, or moving one item closes access to a grazing area, adjust the layout before that conflict becomes part of daily care. Keep enough working room to reach intakes, remove accumulated waste and inspect the structure without repeatedly dismantling the fish’s movement routes.

Finally, consider the system after growth and after all planned residents are present. OATA advises increasing fish numbers slowly because beneficial bacterial populations need to grow as fish and feeding are added. Space and filtration therefore have to work for the completed plan, not just the first day.

Build biological filtration before increasing the load

A mature biological filter is essential. The RSPCA’s aquarium welfare guidance explains that fish release toxic ammonia. Beneficial bacteria in a working filter convert ammonia to nitrite, which is also toxic, and then to the safer nitrate. Clear water is not a substitute for testing those compounds.

Marine filtration may use live rock with sufficient water flow, an internal or external filter, or a sump-based filter. OATA also notes that a protein skimmer can help by removing dissolved organic waste before it breaks down further. Choose the arrangement by its ability to maintain zero ammonia, zero nitrite and nitrate below 50 mg per litre under the intended stocking and feeding load.

Check readiness in three stages

Increase the population slowly. Adding several fish or sharply increasing feeding can leave the bacterial population unable to process the new waste, creating the “new tank syndrome” described by OATA. Adult size matters here: the eventual load must be considered even when the animal entering the aquarium is smaller.

Treat any detectable ammonia or nitrite after an addition as a stop signal for further stocking. Continue testing while the filter and maintenance routine bring both values back to zero. Review uneaten food, blocked intakes and recent cleaning at the same time, because each can change the load or reduce filtration performance. Resume planning only after measurements show that the system is processing its present load consistently.

Prevent blockages through regular filter checks and cleaning. When biological media needs cleaning, rinse it lightly in aquarium water removed during a partial water change rather than under the tap. Chlorine or chloramine in tap water may kill the established bacteria. Clean a protein skimmer regularly so declining performance does not quietly reduce waste removal.

Feed the fish as an algae grazer

FishBase describes this species as a benthic grazer of algae. Make algae the basis of the feeding plan and present it where the fish can graze naturally. Do not turn a general wrasse feeding menu into a parrotfish diet: frozen meaty foods recommended for many wrasses do not replace this species’ recorded algae-feeding biology.

Use feeding behaviour to set each portion

• Offer a portion the fish can consume within a few minutes.
• Watch for active investigation and grazing rather than assuming food has been eaten because it disappears from view.
• Remove accessible uneaten food before it contributes unnecessary organic waste.
• Track body condition and feeding interest together; either one can change before a water-quality problem becomes visually obvious.
• Keep ammonia and nitrite at zero as feeding increases, because the filter must process the resulting waste.

A benthic grazer needs more than food drifting past in open water. Place the algae-based ration so it can be approached from stable, unobstructed areas. If another resident monopolises the feeding point, create separated access while keeping the total ration within what is eaten promptly.

Judge the portion by the fish’s response and by water testing. Food remaining after the feeding window is a reason to reduce the next portion or change how it is presented. A fish that stops grazing, loses condition or shows a marked change in interest needs a water-quality check and closer observation.

Compare feeding observations over time rather than changing the ration from one brief glance. Note whether the fish approaches the grazing point, remains there long enough to feed and leaves accessible food behind. If intake falls while another resident occupies the same area, separate access before increasing the total ration. If food remains despite clear access, reduce the portion and check water values and behaviour for another change.

Do not rely on algae already growing in the aquarium as the entire feeding plan. Its presence and consumption can vary, while the fish’s condition and the filter load still need active monitoring. Keep feeding deliberate, measurable and tied to what the fish actually consumes.

Keep a weekly maintenance rhythm

At least once every week, carry out a partial water change of 25%. Use a siphon where practical to remove solid waste from accessible substrate and low-flow collection areas. The change is a fixed routine, while test results determine whether the system needs closer attention between scheduled maintenance sessions.

Complete the jobs in a consistent order

1. Observe swimming, breathing, colour, body condition and feeding before disturbing the aquarium.
2. Test ammonia, nitrite, nitrate and pH, then compare them with the operating targets.
3. At least once every week, remove 25% of the aquarium water and siphon accumulated solid waste.
4. Use some removed aquarium water to rinse biological filter media lightly when cleaning is due.
5. Check filter intakes, returns and pipework for restrictions or blockages.
6. Clean the protein skimmer regularly so it continues removing dissolved organic waste effectively.
7. Record unusual readings or behavioural changes so a trend is not mistaken for a one-off event.

Do not clean biological media under the tap. Chlorine or chloramine may damage the bacteria that process ammonia and nitrite. Avoid replacing or aggressively cleaning all established media at the same time, because the aquarium depends on that bacterial population as stocking and feeding increase.

Maintenance access should influence the aquascape from the beginning. Leave enough room to siphon waste and reach equipment without dismantling the fish’s main routes. A visually dense layout that cannot be cleaned is a poor trade for a large fish whose feeding adds to the biological load.

Use the weekly record to identify gradual changes. A nitrate result that remains below 50 mg per litre may still be moving upwards from one week to the next, while a pump or skimmer may show a slow decline before it blocks. Compare readings, removed waste and equipment condition with the previous entries. Investigate a trend early rather than waiting for a value to cross its maximum or for water movement to fail.

After any population or feeding increase, use testing to check that the filter remains ahead of the new waste load. The target remains zero ammonia, zero nitrite and nitrate below 50 mg per litre. A stable result over time is more useful than a single acceptable reading taken before the change.

Acclimatise slowly on arrival

Arrange for someone to receive the parcel so live fish are not left unattended. Before delivery, confirm that temperature, salinity and pH are within the intended operating ranges and that ammonia and nitrite are zero.

Follow the current delivery and Live Arrival Guarantee policy. Start filming while the parcel is still sealed, continue in one take through opening it and show the fish inside the sealed bag before anything is disturbed. Then float the 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 parcel so the live fish is not left unattended.
2. Start filming before the sealed parcel is opened.
3. Open the parcel in one continuous take.
4. Show the fish while it is still inside the sealed bag.
5. Float the bag for 20–30 minutes.
6. Release the fish without pouring the bag water into the aquarium.

OATA advises increasing aquarium populations slowly because the beneficial bacteria in the filter need to adjust whenever fish and feeding are added. Do not combine this introduction with several other new fish; a measured introduction also makes it easier to distinguish a compatibility problem from a water-quality problem.

Keep the first observations factual. Note whether the fish swims appropriately, holds its balance, breathes at its usual rate and begins to investigate its surroundings. Changes in those signs belong in the health check below rather than being dismissed as an inevitable part of arrival.

Respond to health changes early

Establish a normal baseline once the fish is settled. Individual fish vary, so the useful warning is a change from that individual’s usual swimming, colour, breathing, feeding, body condition or level of hiding.

Pair each sign with an immediate check

Testing comes first because even small amounts of ammonia or nitrite can stress marine fish. Correcting the environmental problem is different from guessing at a disease treatment, so do not medicate from appearance alone.

If a health change persists, test the water and contact us with the readings, the timing of the change and a clear description of what the fish is doing. Continue the normal observation record while seeking guidance. Exact values and a timeline are more useful than a general statement that the fish seems unwell.

Include feeding in the daily visual check. A benthic algae grazer that loses interest in accessible food, cannot reach its feeding area or is displaced by another resident is signalling a practical problem that should be addressed before condition declines further.

Screen every tank mate against the adult plan

Compatibility must be decided for the actual aquarium and residents rather than from a universal companion list. The first screen is physical: a fish recorded at 50 cm standard length needs turning room, clear movement routes and access to feeding surfaces after every resident reaches adult size.

Compare each proposed resident

• Water overlap: confirm that its routine temperature, salinity and pH requirements overlap the operating range used for this fish.
• Adult space: place both adult sizes into the usable dimensions, not just the nominal volume.
• Feeding access: ensure neither animal blocks the other from its appropriate food or feeding area.
• Waste load: confirm the mature biological filter can maintain zero ammonia and nitrite as stocking and feeding increase.
• Behavioural response: watch for increased hiding, altered aggression, disrupted swimming or reduced feeding after introduction.

OATA’s general marine compatibility advice emphasises that temperament and diet vary by species. That variability is why the names “tang”, “angelfish”, “triggerfish” or “pufferfish” cannot function as automatic approvals. Adult dimensions, individual behaviour and the completed stocking plan matter more than a broad group name.

Work through a proposed addition as a sequence rather than a yes-or-no label. First compare its adult dimensions with the remaining clear routes. Next compare water requirements with 24–26°C, salinity 1.020–1.025 and pH 7.9–8.3. Then identify where each animal will feed and whether both can reach those places without controlling the same narrow passage. Finally, include the extra feeding and waste in the filtration assessment.

Add fish slowly so the biological filter can adjust and so interactions can be observed clearly. If one resident controls a narrow route or feeding station, more nominal litres will not necessarily solve the conflict; the usable layout has to change.

For a stocking and compatibility assessment, contact us with the aquarium’s dimensions, mature filtration, current residents and intended additions. Include adult sizes and the needs of corals or mobile invertebrates rather than relying on purchase sizes.

Treat reef compatibility as case-specific

The confirmed feeding fact is that this species is a benthic grazer of algae. That makes grazing surfaces central to its care, but it does not create a universal reef-safe label. Assess the actual corals, mobile invertebrates, rockwork and feeding arrangement before introducing the fish.

Separate four different questions

Do not infer coral compatibility merely because algae is the recorded wild food. Equally, do not assume that every mobile invertebrate will be taken. The responsible decision is to screen each resident and watch the actual interaction after a slow introduction.

Layout is part of compatibility. Stable structure should preserve access for maintenance and leave more than one movement route. An aquarium can meet its water targets and still create conflict if a large fish and its tank mates must use the same narrow passage or single feeding point.

Use behavioural changes as an early warning. Increased hiding, altered aggression, erratic swimming or reduced food intake after a new addition calls for an immediate interaction check and water test. If the aquarium cannot preserve adult movement, feeding access and stable water for all residents, revise the stocking plan before adding the fish.

Answer the key questions before choosing

What is the Bicolour parrotfish?

It is a marine, reef-associated member of the Scaridae family, endemic to the Red Sea and recorded as a benthic algae grazer reaching up to 50 cm standard length.

How many animals does one purchase supply?

One purchase supplies one Bicolour parrotfish. Sex is not guaranteed for this offer.

How large can Bolbometopon bicolor grow?

FishBase records a maximum of 50 cm standard length, so plan the aquarium around that adult reference.

What aquarium does a Bicolour parrotfish need?

Plan a mature, filtered marine aquarium around a 50 cm adult; OATA’s 150-litre benchmark is for smaller species and says fish over 15 cm need larger systems.

Should it be kept alone or in a group?

Plan this offer per animal rather than as a prescribed group, and add another only after checking adult space, filtration, feeding access and interactions for every fish.

What water does a Bicolour parrotfish need?

Use 24–26°C, salinity 1.020–1.025 and pH 7.9–8.3, with zero ammonia, zero nitrite and nitrate not exceeding 50 mg per litre.

What does this fish eat?

It is a benthic algae grazer. Present algae where it can graze and offer only what it consumes within a few minutes while monitoring body condition and water quality.

How should it be acclimatised?

Start filming before opening the sealed parcel and continue in one take through opening it and showing the fish 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.

Is it compatible with reef residents?

Treat compatibility as case-specific: compare adult space, water overlap, grazing interactions, feeding access and the needs of every coral, mobile invertebrate and fish.

Consult the public references

• FishBase species summary — accepted identity, distribution, environment, wild feeding biology and maximum recorded length.
• Cetoscarus bicolor natural-history summary — family and Red Sea endemism.
• OATA marine guidance — broad water, filtration, maintenance, feeding-amount and introduction principles.
• RSPCA aquarium welfare guidance — biological filtration and nitrogen waste processing.