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Act todayCause not establishedSyndrome — signs cluster, cause is not established

Malawi bloat

The syndrome affects Lake Malawi cichlids in particular, and most seriously the specialised algae-grazing mbuna. These fish have long intestines adapted to processing large volumes of low-protein plant material. Fed on protein-rich foods intended for carnivorous fish, they appear to develop digestive and metabolic problems that end in this presentation. Flagellate organisms are often recovered, but as with hole-in-the-head, their causal role is unclear. What is consistent is the speed — a fish that stops eating and swells is frequently dead within a few days — and the strength of the dietary association.

Short answer

Malawi bloat is a rapidly fatal syndrome of African rift lake cichlids: abdominal swelling, loss of appetite and death within days. Its cause is not settled — diet, water quality, stress and flagellate infection are all implicated — but the association with feeding protein-rich food to species adapted to grazing algae is consistent enough to make diet the first thing to examine.

Syndrome — signs cluster, cause is not established

The signs are consistently reported together, but the underlying cause is not established or varies between cases.

What you can and cannot establish yourself

Suggestive by eye, not conclusive

You can see it, but several conditions look like this. Work through the alternatives below before deciding what you are treating.

Spread between fish
Transmission not established
Urgency
Act today
Affects
fish
Confidence
low confidence

Signs

  • Abdominal swelling, developing over a day or two
  • Loss of appetite, usually the first sign and the one to act on
  • White, stringy faeces
  • Rapid breathing
  • Lethargy and hiding
  • Death within a few days of the first sign
  • Affects rift lake cichlids, particularly specialised algae-grazing species

Do this first: the environmental response

Water quality is the cause, the contributing factor or the deciding variable in the great majority of aquarium health problems. These steps come before any treatment decision, and for several conditions they are the entire treatment.

  1. Review the diet immediately. This is the most consistently supported factor and the one most under a keeper's control.
  2. Test water quality including nitrate, and increase water changes substantially.
  3. Reduce feeding.
  4. Review stocking density and aggression — rift lake tanks are frequently kept crowded by design, which is a management balance rather than an accident.

What else it could be

Every entry names the observation that separates it from this record. Work through these before deciding what you are treating — the most expensive mistake in fish health is confident treatment of the wrong thing.

Non-disease explanations — check these first

  • A gravid or mouthbrooding female

    Not a problemvery common

    How to tell it apart: A mouthbrooding female has a distended throat pouch, not a swollen abdomen, and stops eating for entirely normal reasons. This is much the commonest false alarm in a rift lake tank, and treating a brooding female is both useless and harmful. Look at where the swelling actually is.

Other conditions

  • Constipation from diet

    Named conditioncommon

    How to tell it apart: Constipation develops more slowly and the fish usually continues to feed. Rapid onset with refusal to eat is the pattern that should concern you.

  • Dropsy or organ failure

    Named conditioncommon

    How to tell it apart: Look for scale protrusion from directly above. The two presentations overlap and both are serious.

  • Bacterial infection

    Named conditioncommon

    How to tell it apart: May show reddening or ulceration in addition. Difficult to separate without veterinary investigation, and the two may not be separate.

What makes it more likely

Each entry states the mechanism, not just the association — an association without a mechanism is not something you can act on.

  • Protein-rich diet fed to specialised algae grazers. Mbuna and similar species have digestive tracts adapted to bulky, low-protein plant material. High-protein foods intended for carnivores are consistently associated with this syndrome in them.
  • Overfeeding. Compounds the dietary problem and adds to the organic load in the water.
  • Poor water quality, particularly elevated nitrate. Rift lake cichlids are typically kept at high density in hard alkaline water, where organic load accumulates. The association is consistent though the mechanism is unclear.
  • Chronic stress from inadequate territory or aggression. Associated in reports; mbuna are aggressive and under-sized tanks produce sustained stress.

Treatment categories

AquariumHQ names classes of response and never doses. Product concentrations differ between markets and formulations, several actives are temperature- and pH-dependent, and the invertebrate and plant tolerances that decide whether the rest of the tank survives are not printed on the label. Where a category puts a chemical in the water, what it can damage is stated with it.

Dietary management

Moving specialised grazing species onto an appropriate low-protein, plant-based diet addresses the factor with the most consistent association, and is the main preventive measure.

Correct the husbandry

Improved water quality and reduced organic load are supported as contributing factors and are always appropriate.

Antiparasitic

Adds a chemical to the water

Treatment directed at intestinal flagellates is commonly used and sometimes reported to help, consistent with a parasitic contribution that is not established. Given how quickly this progresses, it is often started before the cause is known.

What it can damage: Antiprotozoal preparations affect invertebrates and can suppress the biological filter. In many jurisdictions the effective preparations are prescription-only.

Do not use

  • Use in place of correcting diet and water quality

Veterinary referral

Worthwhile early rather than late, because the syndrome moves quickly and because the preparations that may help are frequently prescription-only.

Isolation and quarantine

  • Isolating an affected fish allows individual observation and removes it from competition and aggression, which is worthwhile given how quickly this progresses.
  • The tank's diet and water quality affect every fish in it, so the system needs review regardless.

When a vet is the right call

  • Any affected fish, given the speed of progression
  • More than one fish affected, which points at diet or water
  • Where prescription treatment may be needed

AquariumHQ describes what is commonly reported and what husbandry correction is usually indicated. It does not diagnose and is not a substitute for an aquatic veterinarian. Many treatments are given to healthy fish suffering from a water-quality problem, which makes the outcome worse rather than better.

Prevention

  • Feed rift lake grazing species a diet appropriate to their digestive anatomy: low protein, plant-based, and not the food you feed the community tank.
  • Do not overfeed.
  • Maintain water quality despite the high stocking densities these tanks typically run at.
  • Provide enough rockwork and territory to reduce sustained aggression.

What AquariumHQ does not know

Published rather than hidden. A health page that lists no limitations has not had its limitations looked for.

  • The cause is not established. AquariumHQ records the dietary association as the strongest and does not assert that diet is the cause.
  • Whether this is a distinct syndrome or a presentation shared with other causes of abdominal swelling in cichlids is unresolved.

Evidence

Each claim is shown with what kind of support stands behind it and how strongly we hold it. Those are separate axes: a measurement held tentatively and an editorial position held firmly are different things.

Sourced recommendationlow confidenceDisputed

A syndrome of rift lake cichlids without an established single cause; dietary, environmental and parasitic contributions are each proposed

Sources disagree: Aquarium sources commonly present this as a single dietary disease or a single parasitic disease. AquariumHQ records it as unresolved.

  • MSD/Merck Veterinary Manual — fish chapters — Fish — gastrointestinal disorders of cichlids
  • Noga, E.J. — Fish Disease: Diagnosis and Treatment (2nd edn, 2010) — Idiopathic conditions

Last verified 2026-08-11

Sourced recommendationmoderate confidence

Association with protein-rich diets fed to species with digestive anatomy adapted to bulky low-protein plant material is consistently reported

  • UF/IFAS Extension — fish health and aquaculture publications — Ornamental fish nutrition
  • MSD/Merck Veterinary Manual — fish chapters — Fish — nutritional disorders

Last verified 2026-08-11