Keyhole Cichlid (Cleithracara maronii)

Choose a calm cichlid with subtle behaviour

The Keyhole Cichlid (Cleithracara maronii) is a South American member of the cichlid family from the Orinoco delta and rivers extending from Guyana to French Guiana. FishBase records a maximum length of 7.1 cm standard length for male or unsexed fish. It suits a keeper prepared to maintain a biologically mature aquarium, excellent water quality, sheltered structure and carefully screened peaceful companions. This naturally shy fish is generally not aggressive outside breeding, but a breeding pair may defend a territory.

The characteristic dark marking on each side resembles a keyhole, giving the fish its familiar common name. When danger is detected, its pattern may darken considerably and the fish may shelter among plants, submerged wood or leaf litter. Cover is therefore a functional part of the aquarium rather than decoration alone.

Plan the aquarium around recorded growth

The Seriously Fish species profile uses 11 cm standard length as its aquarium-planning reference, compared with the 7.1 cm maximum recorded by FishBase. Use the recorded 7.1 cm adult figure consistently when comparing this animal, while giving it the footprint, cover and community space attached to the more cautious aquarium plan.

Plan movement as carefully as shelter. High flow rates should be avoided, so position the filter return to retain circulation without forcing the fish to remain in a strong current. Plants, wood, pipes or other structures should create retreat areas while leaving usable routes through the aquarium.

Older aquarium literature may place the fish in Acara or Aequidens. Its current scientific name is Cleithracara maronii; those older genera explain why historical labels can look different without representing a different keyhole cichlid.

Match the offer to your aquarium plan

One purchase supplies one Keyhole Cichlid from the size selected on the page. Use the live size selector to choose the dispatch size that fits your aquarium plan.

Read each size choice correctly

The size you select is the size supplied, not the adult size. Use the selected size to understand the animal sent, then plan the permanent aquarium around the recorded adult size and a base measuring at least 90 × 30 cm or equivalent.

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

The gallery images are representative of this type of animal rather than photographs of the exact animal supplied, so colours can look slightly different from the live animal.

Confirm the decisive care figures

• Recorded adult size: 7.1 cm standard length.
• Aquarium base: at least 90 × 30 cm or an equivalent footprint.
• Approximate volume attached to that minimum: about 81 litres.
• Routine temperature: 22–25°C, the overlap of FishBase and Seriously Fish.
• Routine pH: 6.0–7.5, the overlap of FishBase and Seriously Fish.
• General hardness: 2–15 dGH from the Seriously Fish aquarium profile.
• Filtration: biologically mature, maintained and arranged without a high-flow environment.

These figures define a suitable starting point, but the other fish, usable floor area and territorial boundaries still matter. A nominally large aquarium can be unsuitable when aggressive residents dominate it or all cover occupies one small area.

Prepare the aquarium before selecting the animal. Check its measurements, test the water and decide where retreat areas will sit. Read our delivery and Live Arrival Guarantee policy for the current packing, reception, acclimatisation and claim arrangements.

Build around floor area and cover

Start with an aquarium base measuring at least 90 × 30 cm or an equivalent footprint. Seriously Fish associates that minimum with approximately 81 litres, but the base dimensions remain the important planning figure because structure, territories and sheltered routes all use horizontal space. Increase the footprint when other fish or several keyholes must share the layout.

The aquarium must be biologically mature before this cichlid is introduced. If you are preparing a new system, follow our first tropical aquarium guide before choosing an introduction date.

Create several kinds of shelter

A soft sandy substrate supports a natural-looking display, while OATA’s American-cichlid advice also permits fine aquarium gravel or sand. Choose aquarium-safe material and keep enough exposed base for routine waste removal. Because keyholes tend not to dig, most planted aquariums can work when the plants also leave navigable routes between shelters.

Divide shelter across the aquarium

Spread structure across the footprint rather than concentrating every retreat in one corner. Several separated shelters allow a shy fish to move away from disturbance without crossing an entirely exposed tank. Wood, planting and upright décor can interrupt direct views while preserving access for cleaning.

Keep the layout practical. Place shelters where you can still observe breathing, body condition and feeding, and leave access around the filter intake. If breeding is not part of the plan, flat surfaces remain optional; cover and water quality are the essential elements.

Do not compensate for a small footprint by filling the aquarium densely with décor. The minimum base must still provide usable movement and distinct retreat areas after wood, plants and equipment are installed. Measure the clear internal footprint, sketch where the main structures will sit and check that the fish can pass between them without entering a high-flow zone.

Choose water values the fish can share

Keep Cleithracara maronii at 22–25°C and pH 6.0–7.5. These routine values are the overlap of FishBase’s recorded range and the Seriously Fish aquarium range. Use 2–15 dGH for general hardness, as given by the species aquarium profile.

OATA’s American-cichlid sheet gives 22–27°C, pH 6.5–8.0 and 4–12 dGH as group guidance. Those figures can help with community screening, but this fish’s routine temperature must remain within 22–25°C and its pH must not exceed 7.5.

Work from measured water

Test the aquarium rather than choosing a target from appearance or a general description such as soft water. Our water chemistry guide explains what the measurements mean, while the water matcher can compare your readings with the stated range.

A reading inside these ranges is only one part of the decision. Ammonia and nitrite must both be zero, and the filter must be mature enough to process the waste created by the complete stocking plan. Temperature, pH and hardness must also suit every peaceful companion being considered.

Avoid chasing a particular number merely because it appears in the middle of a range. Select a workable point that your aquarium can maintain, then test regularly so a change is noticed before it becomes a welfare problem. For a community, use the narrow overlap shared by every resident rather than selecting a different target for each fish.

Establish the biological filter before introduction

Never introduce a Keyhole Cichlid to a biologically immature aquarium. Water quality is particularly important for this species, and deteriorating conditions are associated with health problems. A clear-looking aquarium is not necessarily biologically ready, so use test results and filter maturity rather than appearance.

The RSPCA explains why aquarium filtration is vital: fish release toxic ammonia, biological-filter bacteria convert it to toxic nitrite and another stage converts nitrite to the safer nitrate. Both ammonia and nitrite must read zero before the animal is introduced.

Use a pre-introduction checkpoint

Do not add several unplanned fish at the same time simply because the aquarium previously tested well. OATA warns that increasing livestock too quickly can cause new tank syndrome when nitrifying bacteria cannot process the additional waste. Treat each addition as a change in the load placed on the biological filter.

Interpret test results before acting

If ammonia or nitrite is above zero before introduction, postpone the stocking step and restore biological performance. Check that the filter is operating, has not been run under the tap and is not blocked. Retest after the system has stabilised rather than relying on a single improved reading.

Nitrate is managed through maintenance rather than by the first two stages of the biological filter. OATA advises that it should not exceed 20 mg/l above the normal tap-water level. Test the tap water as the comparison point: if tap water measures 10 mg/l nitrate, the group ceiling works out at 30 mg/l in the aquarium.

These readings have different jobs. Zero ammonia and zero nitrite are immediate prerequisites, while the nitrate comparison helps assess whether water changes and stocking are keeping accumulated waste under control.

Balance turnover, heat and weekly maintenance

For an aquarium of about 81 litres, the species profile uses a filter turnover of four to five times the aquarium volume each hour. That calculation gives approximately 325–405 litres per hour. Treat the rating as an equipment starting point, then arrange the return so the fish is not forced to live in a strong current.

Position equipment around the fish

• Filter return: direct or diffuse the output to avoid a high-flow environment while retaining circulation.
• Filter intake: leave it accessible for blockage checks and keep décor from obstructing it.
• Heater: choose equipment capable of maintaining the routine 22–25°C range in the aquarium and room conditions concerned.
• Thermometer: use the measured temperature to confirm that the chosen setting stays within range.

Filter ratings do not guarantee identical real-world flow after media, pipework and head height are considered. Observe whether the sheltered areas remain calm and position the return accordingly. Reducing an uncomfortable jet is different from turning filtration off; biological filtration must continue operating.

Complete maintenance at least once a week

OATA strongly recommends a 25% water change at least once a week. In an 81-litre aquarium, 25% is approximately 20.25 litres. The exact amount in practice depends on the aquarium’s true water volume after substrate and décor, but the calculation gives a useful preparation figure for buckets and conditioner.

Chlorine or chloramine can harm the beneficial bacteria living in filter media. Avoid replacing or aggressively cleaning all media during routine maintenance because biological performance depends on retaining that population. Link each task to a measurement or observation: test the water, inspect the filter, remove accumulated waste and confirm the temperature after replacement water is added.

Feed a varied omnivore diet once daily

Keyhole Cichlids forage as omnivores, taking benthic invertebrates and organic detritus in nature. FishBase also records worms, crustaceans and insects in the wild diet. In an aquarium they accept most prepared foods, but variety is important for good condition. Use a quality dried product as part of the diet and rotate suitable live or frozen items.

Build variety from supported foods

OATA’s group feeding schedule is once a day, offering only what the fish can eat within a few minutes. Start with a modest amount, observe the response and stop before uneaten food accumulates. Keyholes can be shy, so watch whether the individual actually reaches the food rather than judging the portion only by how quickly the whole community clears it.

Use the aquarium response to adjust the portion

• If food remains after a few minutes, reduce the next portion and remove accessible leftovers.
• If faster companions take every item, reassess the community and food distribution rather than automatically adding a larger total quantity.
• If the fish loses interest in food, treat that change as a health or water-quality prompt.
• If waste and nitrate rise despite maintenance, review both the portion and total stocking load.

Overfeeding creates more faeces and leaves uneaten food to break down, adding waste that the biological filter must process. A large single meal is therefore not a shortcut to good condition. The useful measure is whether the fish receives a varied diet while the aquarium remains clean and chemically stable.

Do not rely on one favourite frozen food as the entire diet. Rotate it with quality dried products and other suitable items so “varied” describes the feeding pattern across time, not the number of foods tipped into one meal. Keep pieces bite-sized and observe body condition alongside appetite during the regular health check.

Make the first week calm and measurable

Prepare the receiving aquarium before the fish arrives: confirm a base of at least 90 × 30 cm, mature biological filtration, 22–25°C water, pH 6.0–7.5, hardness of 2–15 dGH and zero ammonia and nitrite. Check that cover is distributed across the aquarium and that the filter return does not create a high-flow zone.

Introduce this animal as one planned stocking step rather than combining it with several unrelated additions. Beneficial bacteria need to respond as waste and feeding increase, so slow stocking protects the biological filter from a sudden load.

Use a first-week observation plan

Hiding is a behaviour to interpret, not a reason to remove all shelter. Keyholes use cover when they perceive danger, and taking that cover away can leave the fish more exposed. Instead, examine whether aggressive behaviour, excessive flow or a poorly divided layout is preventing normal movement.

Keep the first week predictable. Complete essential maintenance without repeatedly disturbing every shelter, and observe from enough distance to see whether the fish emerges, feeds and moves normally when the aquarium is calm. Record the test results so a later change can be compared with a real baseline.

If the pattern darkens only during a disturbance and the fish later resumes feeding and ordinary movement, continue observation while keeping the aquarium calm. If dark colour accompanies abnormal breathing, damaged fins, loss of appetite or persistent isolation, move to the health-response checks rather than assuming shyness explains everything.

Respond to changes before they escalate

Learn the individual fish’s usual swimming, colour, breathing, appetite and use of cover. OATA notes that fish vary in behaviour and appearance, so the useful warning is often a change from the established pattern rather than one isolated pose.

Pair each warning sign with an immediate check

When a health change appears, test ammonia and nitrite first because even small amounts can stress American cichlids. Compare nitrate with the tap-water baseline, confirm temperature remains within 22–25°C and check that the filter has not become blocked.

Do not interpret every darkening event as disease. The species may darken considerably and take cover when it detects danger. Context matters: look at what happened immediately beforehand, whether another fish approached and whether ordinary movement and feeding resume.

Conversely, do not dismiss a cluster of signs as shyness. Dark colour combined with rapid breathing, appetite loss or damaged fins calls for immediate water testing and a review of the community. Record when the change began and the measured water values; concrete observations make the next decision more precise.

If you are concerned about a health change, test the water and contact us for guidance. Avoid selecting a treatment from appearance alone because different problems can produce similar behaviour, and maintaining safe water remains the first practical step.

Screen every community companion

Keyhole Cichlids are generally not aggressive unless breeding, and the species profile considers most peaceful fish sharing similar environmental conditions as possible companions. That is a screening starting point rather than a universal tank-mate guarantee because behaviour, adult size, water chemistry and the complete stocking plan still matter.

Apply four compatibility tests

Open-water characids or similar calm schooling and shoaling fish are particularly recommended in the species profile. Their presence may act as a cue that no threat is nearby, encouraging a shy keyhole to behave more confidently. This benefit still depends on those fish sharing the water conditions and not overwhelming the cichlid at feeding time.

Do not choose companions solely because they come from South America or carry a “community” label. Geographic association does not settle adult size, aggression, feeding competition or water requirements. Compare the actual needs of each fish and assess the aquarium as one community.

Review the physical layout with the stocking list

A peaceful combination can still fail if all fish compete for the same sheltered area. Provide several retreats, keep calm open-water space for suitable shoaling fish and ensure no resident controls every route between cover and food.

Compatibility remains conditional on individual behaviour and the full aquarium plan. Ask us for a stocking assessment with the aquarium dimensions, measured water values and complete resident list. To research other profiles without assuming they are compatible, browse the South American cichlid collection.

Plan pairs, groups and breeding territories

Juvenile Keyhole Cichlids are gregarious, but the species profile presents a group of young fish primarily as a route to natural pair formation. Pairs should be separated as they form. A group purchase therefore requires spare aquarium capacity and a realistic separation plan rather than an assumption that every fish will remain together indefinitely.

Choose the social plan before adding fish

OATA’s group guidance says most American cichlids do better singly or in pairs, while the dedicated profile explains the juvenile-group route used for this animal. Use those statements according to the plan: a permanent group and a temporary pair-forming group are not the same arrangement.

This fish is a biparental, monogamous substrate spawner. Eggs may be laid on a flat rock, driftwood, a broad plant leaf or aquarium glass, and both parents participate in reproduction. Young or inexperienced pairs may eat early broods if they feel threatened or are disturbed.

Expect behaviour to change during breeding

The normally peaceful disposition does not remove territorial behaviour around a spawning site. If a pair begins cleaning or defending a surface, reassess the routes used by every other resident. A community that worked outside breeding may need separation once a territory is established.

Do not use litres alone to plan several fish. Floor area, separated shelters and the ability to move a pair safely are the decisive resources. Starting with the approximately 81-litre minimum for one suitable setup does not create a formula in which each additional fish can simply be assigned another fixed number of litres.

Keep the offer terms separate from the social plan. Each purchase supplies one animal, and its dispatch size does not establish a pair bond, maturity or sex. Build any breeding plan around observed pair formation and sufficient separation capacity.

Answer key buyer questions

How big does the Keyhole Cichlid get?

FishBase records the Keyhole Cichlid at up to 7.1 cm standard length. Seriously Fish uses 11 cm standard length as a cautious aquarium-planning reference, so provide the full recommended footprint rather than planning around its dispatch size.

What size aquarium does the Keyhole Cichlid need?

Use an aquarium with a base of at least 90 × 30 cm or equivalent, associated with approximately 81 litres by Seriously Fish. Provide mature biological filtration, sheltered structure and a filter return arranged to avoid high flow.

How many Keyhole Cichlids should I keep together?

OATA’s American-cichlid group guidance supports single or pair keeping. Seriously Fish says a group of young fish can be used for natural pair formation, but pairs should be separated as they form, so that plan needs a larger structured aquarium and spare capacity.

Is the Keyhole Cichlid suitable for a beginner?

A careful beginner can consider it after establishing a biologically mature aquarium and learning to test water consistently. It needs zero ammonia and nitrite, excellent water quality, cover, restrained flow and carefully screened companions.

What does the Keyhole Cichlid eat?

Feed it once daily and give only what it can eat within a few minutes, following OATA’s American-cichlid schedule. Use a varied omnivore diet with quality dried food plus suitable bloodworm, Artemia and Daphnia in live, frozen or freeze-dried forms.

What temperature and pH does it need?

Keep it at 22–25°C and pH 6.0–7.5, the overlap of FishBase and Seriously Fish, with 2–15 dGH from the Seriously Fish aquarium profile. Ammonia and nitrite must remain at zero mg/l.

Is it aggressive or likely to nip fins?

It is generally not aggressive unless breeding, when a pair may defend a territory. Avoid aggressive or territorial fishes, provide several retreat areas and reassess the community if breeding behaviour begins.

Which kinds of animals can it live with?

Consider peaceful fish that share 22–25°C, pH 6.0–7.5 and 2–15 dGH; Seriously Fish particularly recommends open-water characids or similar calm shoaling fish. Avoid aggressive or territorial fish and species requiring harder water, while treating fish only a few millimetres long with caution.

How does this fish arrive alive in the UK?

Tropical Fish Co’s policy requires someone to be present to receive the parcel. Start filming every delivery before opening it and continue in one take from the sealed parcel through opening, with the animal 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.

References for identity and care

• FishBase: Cleithracara maronii — taxonomy, family, distribution, recorded environment, wild biology and maximum recorded length.
• Seriously Fish: Cleithracara maronii — aquarium dimensions, water range, décor, feeding, behaviour, compatibility and reproduction.
• OATA: How to look after American cichlids — group guidance on water testing, maintenance, feeding, introduction and welfare observations.
• RSPCA aquarium environment guidance — biological filtration and the aquarium nitrogen cycle.