Black Pearl Calvus (Altolamprologus calvus)

Recognise a rock-dwelling Tanganyika predator

Black Pearl Calvus is a dark aquarium form of Altolamprologus calvus, a freshwater cichlid endemic to the south-western part of Lake Tanganyika. Its deep, laterally compressed body allows it to enter narrow cracks and shallow caves. The steep forehead, tall dorsal profile, dark vertical bars and pale pearling give this form its distinctive appearance. It suits keepers who can maintain stable hard alkaline water, extensive rocky cover and carefully screened Tanganyika companions.

FishBase records a maximum of 13.5 cm total length for a male or unsexed fish. It also describes the wild fish cruising through rocky habitat while maintaining a distance of 30–100 cm from the substrate. Shrimps and other crustaceans make up its main natural diet, so its deliberate hovering and short stalking movements are purposeful rather than inactivity.

This body shape determines the aquarium plan. Provide rock faces, shaded retreats and gaps that the fish can explore without becoming trapped. Leave open routes between structures so it can move around its territory and withdraw from companions. A bare aquarium removes the cover around which its natural behaviour is organised.

The black form is one of several recognised aquarium colour forms. Treat Black Pearl as a colour-form name rather than a collection-locality guarantee. Build the care plan around Altolamprologus calvus, its adult size and its rocky Lake Tanganyika habitat.

Understand the animal you order

One purchase supplies one Black Pearl Calvus. The fish is supplied at 3–4 cm; this is its dispatch size rather than its adult size. Choose the purchase quantity by the number of animals required, while allowing separately for the social and territorial needs of every fish in the final plan.

Complete the adult aquarium, filtration and rock layout before introduction rather than treating the smaller dispatch size as suitable for temporary cramped housing.

Sex is guaranteed only when the selected option explicitly states male or female. This Black Pearl Calvus 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.

Darkness, visible bars and pearling can vary with the individual, lighting and surroundings. Use the gallery to recognise the intended dark, spotted form, but use the scientific name when making practical decisions.

Decide whether your aquarium fits the adult fish

This cichlid suits an established Lake Tanganyika-style aquarium with hard alkaline water, extensive rocky cover and companions chosen for calm behaviour. It is territorial but is described as generally peaceful towards fish it cannot fit into its mouth. Its shy, deliberate feeding style makes protection from aggressive or very vigorous competitors particularly important.

The Seriously Fish species account recommends a Lake Tanganyika biotope with piles of rocks forming caves. It describes pair or colony keeping in a suitably sized aquarium, making territory layout and a separation plan more useful than relying on a nominal fish count.

Measure the aquarium’s water and assess its usable rocky territory before adding the fish. If the chemistry needs repeated abrupt correction, the rockwork leaves no escape route or existing fish monopolise food, resolve that problem first.

Build caves with usable routes between them

Arrange piles of rocks to form caves across much of the aquarium. The aim is not simply to add decoration: the structures create the narrow gaps, shaded resting places and broken sight lines around which this fish feeds and establishes territory.

Create several distinct choices

Use more than one cave entrance and divide the rockwork into separate zones. A fish should be able to leave one retreat and reach another without crossing an entirely exposed aquarium. Open routes between the structures also let you observe swimming, feeding and body condition.

Keep each accessible space free from sharp obstructions. Arrange heavy pieces firmly before routine maintenance begins, then check them after any disturbance. Solid placement matters because waste removal and territory rearrangement should not create a collapse risk.

Test the route before introduction

Look through the aquarium from both ends before the fish arrives. If one rock pile blocks every route or one cave is the only shaded refuge, divide the structure and create another usable choice. Check that the fish could withdraw behind cover without entering a dead end and that you can still reach areas where uneaten food may settle.

Recheck the same routes after maintenance. A moved stone can close an entrance, expose a retreat or direct one fish into another territory. Restoring the intended layout immediately is safer than waiting for exclusion or chasing to reveal the problem.

Balance shadow with observation

Dim lighting encourages this naturally shy fish to show itself more often. A dark substrate can also display the black form effectively. Provide shadow beneath overhangs while retaining enough light and open frontage to examine the eyes, fins, scales, breathing and feeding response.

Plants are not needed to reproduce the essential habitat. Prioritise functional caves and rock faces rather than letting planting block entrances or trap food. Leave room around the structures for circulation and routine waste removal.

Set a stable hard-water range before introduction

Keep this fish at 24–25°C, pH 8.0–8.6 and 12–18 dGH. FishBase records 23–25°C, pH 8.0–9.0 and 9–19 dH for the wild environment, while Seriously Fish gives aquarium ranges of 24–27°C, pH 7.5–9.0 and 8–20 dGH. OATA’s African lake cichlid sheet gives 23–27°C, pH 8.0–8.6 and 12–18 dGH as group guidance. The routine values are the overlap of all three.

Prepare repeatable replacement water

Test the aquarium and replacement water rather than adjusting by appearance. Our water chemistry guide explains the role of pH, GH, KH, ammonia, nitrite and nitrate. The water matcher then helps compare measured values with this routine range.

For example, aquarium water at 24°C, pH 8.3 and 15 dGH sits within the working range. Prepare replacement water close to those values so a normal water change maintains stability instead of creating a sudden swing.

Compare trends as well as single readings

Write down the readings before and after routine maintenance. If pH, hardness and temperature remain close from one week to the next, the preparation method is repeatable. If the same value repeatedly moves towards the edge of the range, examine replacement-water preparation, maintenance timing and waste accumulation before making another adjustment.

A single acceptable reading does not replace regular testing. The useful pattern is stable hard alkaline water, ammonia and nitrite held at 0 mg/L, and nitrate controlled through maintenance. Test again after a significant stocking or feeding change because the biological load has changed even when the water still looks clear.

Respond to results in the right order

Any detectable ammonia or nitrite needs immediate attention to filtration, stocking, feeding and maintenance. A rising nitrate trend calls for timely partial water changes and removal of trapped waste. Avoid repeated abrupt pH correction; prepare water consistently and confirm each adjustment with a test.

Protect the biological filter and oxygen supply

RSPCA aquarium welfare guidance explains that fish release toxic ammonia and that a working biological filter supports bacteria which convert it to nitrite and then nitrate. Run a mature, maintained filter continuously and establish it before the fish arrives.

OATA recommends an oversized filter for crowded African lake cichlid communities and vigorous aeration to maintain dissolved oxygen. Position the outlet or an air source to keep the surface moving, while leaving calmer areas beside caves where the fish is not pushed continuously by the current.

Make maintenance predictable

• Change 25% of the water at least once a week.
• Treat replacement tap water with conditioner to remove chlorine or chloramine.
• Test ammonia and nitrite at least weekly and whenever behaviour changes.
• Check the filter for blockages and remove solid waste from accessible areas.
• Rinse filter media lightly in aquarium water removed during a water change, not under the tap.

Cleaning every filter component at once can remove too much of the established bacterial population. Preserve biological media while clearing enough mechanical debris to keep water moving. If flow has weakened, check intakes, trapped waste and blocked media rather than assuming the filter is still operating at full capacity.

Link each observation to an action

Clear water alone is not a measure of biological performance. Use test results, steady flow and the fish’s breathing and feeding behaviour together. This separates a filter that merely moves water from one that is supporting the aquarium’s waste load.

Judge readiness by performance

Follow our first tropical aquarium guide to prepare and mature the system. Readiness means the filter is running reliably, ammonia and nitrite remain at 0 mg/L, temperature and mineral values are stable, and all rockwork is complete.

Increase livestock gradually. Every added fish and extra feed increases the load on the filter bacteria. A slow stocking sequence gives the biological filter time to respond and makes it easier to identify which change preceded a water-quality problem.

Feed a deliberate crustacean predator without waste

In Lake Tanganyika, Altolamprologus calvus feeds mainly on shrimps and other crustaceans. Its compressed body lets it approach prey around cracks and rock faces. Build the aquarium diet around appropriately sized meaty live and frozen foods rather than expecting it to compete for plant-based food or scavenge leftovers.

Seriously Fish reports that meaty live and frozen foods are readily accepted and that dried varieties are not usually taken. OATA includes frozen brine shrimp, prawns and cockles among suitable foods for predatory African lake cichlids. Introduce one suitable food at a time and watch the fish swallow it before adding more.

Use the same portion rule at each meal

Feed twice a day, offering only what the fish can eat within a few minutes. Begin with a small amount close to its rocky territory. If every piece is consumed promptly and the fish remains engaged, add another small portion. Stop when interest falls rather than allowing food to settle into caves.

Check that feeding reaches the intended fish

In a community, watch the Black Pearl Calvus rather than the food alone. A meal can disappear within minutes while a shy fish receives nothing. Occupy faster companions away from the rocks, then place a measured portion near the Calvus territory and confirm that it eats.

Use the same observation point for several meals. A steady response makes a later change easier to recognise, while repeated food refusal points to a need to check food type, water quality and social pressure. Remove food lodged in caves before it breaks down.

Overfeeding creates uneaten material that breaks down and adds toxic waste to the water. Do not add a large compensatory meal after one quiet feed. Record what was offered and eaten so a genuine change in appetite is clear.

Prepare a calm first day before opening the bag

Complete the aquarium before delivery day. Confirm 24–25°C, pH 8.0–8.6, ammonia at 0 mg/L and nitrite at 0 mg/L. Check filter flow, secure the cave layout and leave an unoccupied retreat that the fish can reach immediately.

Arrange for someone to receive the parcel because live fish must not be left unattended. Read the current delivery and Live Arrival Guarantee policy before the delivery window so the arrival and claim steps are understood in advance.

Follow the store acclimatisation sequence

1. Start filming before the sealed parcel is opened and keep the video continuous as the parcel is opened and the fish is shown inside the sealed bag.
2. Open and inspect the parcel on the day it arrives.
3. Float the bag for 20–30 minutes before releasing the fish.
4. Never pour the bag water into the aquarium.
5. Transfer the fish gently and allow it to find cover.

Seriously Fish advises dim lighting for this shy species. Keep observation calm while it settles and avoid chasing it back into view.

Use behaviour as a first-day checkpoint

A rock-associated fish may remain close to a cave or vertical surface after transfer. Observe breathing, posture and balance without repeatedly disturbing its retreat. Hiding by itself is less concerning than hiding combined with rapid breathing, damaged fins, erratic swimming or an inability to hold position.

Keep the first checks simple

• Confirm that the fish can hold position and reach a secure cave.
• Check that no resident fish blocks the retreat or begins sustained chasing.
• Watch breathing from a distance before approaching the aquarium again.
• Test ammonia and nitrite if behaviour changes or breathing remains unusually fast.
• Remove any uneaten food before it settles among the rocks.

A calm first day gives the fish time to orient around the cave system. Repeatedly moving décor, increasing the lighting or trying to force it into open water removes that opportunity. Make only the change needed to correct an immediate water, equipment or aggression problem.

Keep feeding restrained during the settling period. When food is offered, place a small amount near cover and confirm whether it is eaten. Remove leftovers promptly, because a newly introduced fish and an increased feeding load both affect water quality.

Use first-week and first-month checkpoints

Look for trends rather than judging health from colour alone. African lake cichlids vary naturally in appearance and behaviour, but changes in swimming, breathing, appetite, condition or temperament can reveal a developing problem.

During the first week

• Confirm that the fish can enter and leave a secure retreat.
• Watch the gill covers at rest for a marked increase or decrease in breathing rate.
• Check whether it reaches food without being displaced by faster companions.
• Inspect the eyes, fins and scales for damage, white spots, fluffy growths, ulcers or bumps.
• Test ammonia and nitrite whenever behaviour or appetite changes.
• Remove trapped food and check that filter flow remains steady.

During the first month

Compare body condition from week to week. A fish that repeatedly approaches food but never eats may dislike the food, be intimidated by another fish or be affected by water conditions. A fish that stays pinned at the surface, behind equipment or in one exposed corner needs prompt assessment of aggression and territory access.

Record weekly pH, nitrate and maintenance alongside feeding and behaviour. This makes a gradual water trend or social change easier to recognise. Continue the 25% partial water change at least once a week, condition tap water and clean blocked media only in removed aquarium water.

Use a repeatable weekly review

Make the same checks before changing the aquarium: water readings, filter flow, breathing, appetite, body condition and access to cover. A consistent sequence helps distinguish a one-off startle response from a trend that needs action. Note recent livestock additions or feeding changes beside the results because either can alter filtration demand and social pressure.

If the fish feeds but loses access to its retreat, treat the territory problem separately from diet. If it hides securely but stops eating and breathes rapidly, test the water and check aeration before changing the rockwork. Matching the response to the observed change avoids several disruptive adjustments at once.

Plan pairs and colonies around changing territories

Seriously Fish describes this species as suitable for maintenance as a pair or colony in a suitably sized aquarium. That does not make any two individuals a compatible pair or turn a purchase quantity into a social recommendation. Build several territories and retain a practical way to separate fish if behaviour changes.

Males grow larger and develop longer fins than females, but those adult differences should not be used to assign sex to the animal supplied. Do not infer sex from colour, size or the gallery when a sex-specific plan matters.

Watch access, not just chasing

Territorial failure is often visible through exclusion. One fish may control the only secure cave, intercept food or force another fish to remain near the surface. Persistent loss of access to food and cover requires separation even before torn fins appear.

• Provide multiple cave entrances and broken sight lines.
• Check that every fish can reach food during both daily feeds.
• Separate a fish that is repeatedly cornered or prevented from feeding.
• Reassess the layout when a pair claims a breeding cave.
• Do not rely on extra food to resolve territorial pressure.

Keep colour forms separate

Several geographic colour forms occur in the aquarium trade. Seriously Fish advises that these forms should not be allowed to hybridise and should not be kept together. Maintain Black Pearl Calvus separately from other A. calvus forms where reproduction could occur.

Breeding behaviour can intensify defence of a cave. Flowerpots or shells may form breeding cavities, but adding another cavity does not guarantee that incompatible fish will coexist. Territory, adult size, feeding access and a prompt separation option remain the practical safeguards.

Screen every tank mate by size, pace and territory

This fish is territorial but generally peaceful towards fish it cannot fit into its mouth. That makes adult size the first compatibility screen. Small fish, fry and ornamental crustaceans are exposed to predation because A. calvus naturally eats shrimps and other crustaceans and enters crevices to prey on eggs, fry and small fish.

Temperament and feeding pace form the second screen. Seriously Fish specifically says to avoid aggressive or very vigorous tank mates such as mbuna because this species tends to be shy. A companion that consumes every meal or repeatedly drives the Calvus away from rock cover is unsuitable even when it is too large to swallow.

OATA recommends keeping African lake species with fish from the same location and does not generally recommend mixing Malawi and Tanganyika cichlids because their temperament and behaviour differ. Shared hard alkaline water alone is not enough.

Run the screen before changing the stocking plan

Compare the proposed companion at adult size, not dispatch size. Then ask whether it can use the same 24–25°C, pH 8.0–8.6 and 12–18 dGH routine range, whether it feeds at a compatible pace and whether the rock layout leaves each fish a usable territory.

Reject the combination if one animal is likely to be swallowed or if the companion is an aggressive, very vigorous competitor. Where the basic screen is passed, keep separation capacity ready and watch access to food and caves after introduction. A pairing that works at first can still change as territories develop.

Compatibility remains individual and conditional. Screen the final stocking list by adult size, water needs, aggression, feeding speed and territory, then contact us for a stocking and compatibility assessment if the combination is uncertain.

Sequence a Tanganyika community to reduce pressure

Begin with a restrained Lake Tanganyika plan rather than treating every African cichlid as interchangeable. The African cichlid collection is useful for browsing identities, but a shared collection does not make two fish compatible.

Compare each candidate before purchase

• Adult size: reject fish small enough to be swallowed and allow for the Calvus maximum of 13.5 cm total length.
• Water: keep every species within 24–25°C, pH 8.0–8.6 and 12–18 dGH if using this routine Calvus range.
• Feeding: make sure the deliberate Calvus can receive meaty food before vigorous fish take it.
• Territory: allocate separate rock zones, caves and routes rather than one structure controlled by a single fish.
• Response plan: keep a safe means of separation ready before introducing a pair, colony or community.

Add fish in a considered order

OATA recommends adding more peaceful African lake species first and more aggressive species later. Increase the population slowly so the biological filter can respond to each rise in waste and feeding. Rearranging décor before an introduction may reduce established territorial ownership, but every rock must remain stable and the resident Calvus must retain secure cover.

After an addition, watch both meals each day. Check whether every fish leaves cover voluntarily, reaches food and withdraws without sustained pursuit. Separate a fish that is continually cornered, pinned near the surface or losing condition.

Review the result after each addition

Do not judge the combination only during the first minutes. Check the next feeds, resting places and movement between caves. A resident that initially retreats may settle, but repeated exclusion from food or cover shows that the introduction is not working.

Test ammonia and nitrite after the stocking change and keep the normal maintenance schedule. Adding fish increases both social pressure and biological load, so a change in breathing or appetite needs a water-quality check as well as a behaviour check. Make the next addition only after the aquarium has returned to a stable routine.

Named genera sometimes kept in Tanganyika communities still require this full screen. Adult size, individual behaviour and the exact layout determine the result; a familiar common name is never a universal compatibility guarantee.

Answer practical Black Pearl Calvus questions

How big does Black Pearl Calvus get?

FishBase records a maximum of 13.5 cm total length for Black Pearl Calvus. Plan the aquarium around that adult size rather than its 3–4 cm dispatch size.

What size aquarium does Altolamprologus calvus need?

Use a suitably sized mature aquarium that can hold extensive rock piles, several caves, open routes and separate territories for every fish. Seriously Fish bases the setup on a Lake Tanganyika biotope and describes pair or colony keeping only in suitably sized accommodation.

How many Black Pearl Calvus should I keep together?

Seriously Fish describes pair or colony keeping in a suitably sized aquarium. Any pair or colony needs divided rocky territories and a practical separation plan because individual fish are not automatically compatible.

Does this fish suit beginners?

It suits a keeper who can maintain 24–25°C, pH 8.0–8.6 and 12–18 dGH, run a mature biological filter and monitor a shy territorial predator at every feed.

What does Black Pearl Calvus eat?

Feed appropriately sized meaty live and frozen foods twice daily, offering only what it can eat within a few minutes. FishBase records shrimps and other crustaceans as its main natural diet, while Seriously Fish reports that dried foods are not usually accepted.

What temperature and pH does this fish need?

Keep it at 24–25°C, pH 8.0–8.6 and 12–18 dGH, the overlap of FishBase, Seriously Fish and OATA’s African lake cichlid group guidance. Maintain ammonia and nitrite at 0 mg/L.

Is Altolamprologus calvus aggressive or likely to nip fins?

It is territorial but generally peaceful towards fish it cannot swallow. The practical risks are predation on small animals and exclusion from food or caves, so separate any fish that is repeatedly chased, cornered or prevented from feeding.

Which animals can this fish live with?

Consider calm Tanganyika fish too large to swallow and able to share its water, feeding pace and rocky territory. Seriously Fish names Julidochromis, Neolamprologus, Cyprichromis and Tanganyikan Synodontis as possible choices; avoid mbuna, small fish, ornamental crustaceans and other Calvus colour forms where hybridisation could occur.

How does this fish arrive alive in the UK?

Tropical Fish Co hand-packs live fish in oxygen inside an insulated box, using a heat pack when the weather calls for it. Someone must be present to receive the parcel. Start filming every delivery before opening the sealed parcel, continue as it is opened and show the fish still inside the sealed bag; then float the bag for 20–30 minutes and never pour the bag water into the aquarium.

Consult the care references

• FishBase — Altolamprologus calvus: scientific identity, family, Lake Tanganyika distribution, maximum recorded length, wild environmental values, habitat and natural diet.
• Seriously Fish — Altolamprologus calvus: aquarium water ranges, rocky setup, feeding, behaviour, compatibility, sexual dimorphism and colour-form management.
• OATA — How to look after African lake cichlids: UK group care guidance for water quality, feeding frequency, filtration, aeration, maintenance, introductions and community planning.
• RSPCA — Creating a suitable fish environment: general aquarium welfare guidance on biological filtration and toxic nitrogen waste.
• Tropical Fish Co delivery policy: packing, receiving, 20–30 minute floating and Live Arrival Guarantee requirements.