Malawi bloat: signs, causes, treatment and prevention in mbuna and Tropheus

Malawi bloat is a fast-moving gut disease of African rift-lake cichlids, especially plant-eating mbuna and Tropheus. If a fish stops eating, hangs back and passes white stringy poop, treat it as urgent: once the belly visibly swells, many fish die within a few days.

No single germ causes it. Vets and experienced keepers link it to the wrong diet, stress and poor water, which let gut parasites and bacteria take over. Early treatment, usually the drug metronidazole given in food, saves some fish. A proper herbivore diet prevents most cases.

How to identify it

Malawi bloat mostly affects cichlids from Lakes Malawi and Tanganyika that graze algae in the wild: mbuna (Pseudotropheus, Maylandia, Labeotropheus and relatives) and Tropheus. Watch for these signs, roughly in the order they appear:

Loss of appetite: the fish takes food and spits it out, or ignores it. This is the earliest and most useful warning.
Hiding or hanging near the surface or in a corner, with dull or darkened colours.
White, stringy or clear poop instead of normal dark, solid droppings.
Fast breathing: the gill covers pump hard even when the fish is still.
A swollen belly: a rounded, bloated abdomen. By this stage the disease is advanced.
Late signs: a red or swollen vent, gut tissue protruding from the vent, and sometimes raised scales (see dropsy).

A fat fish that eats eagerly is probably just well fed or a female carrying eggs (mbuna females hold eggs and fry in their mouths, which swells the throat, not the belly). A fish that is bloated and not eating is the worry. For other kinds of swelling, see bloated fish.

When it's a problem

Early: one fish refuses food for a day and has pale poop. This is the best time to act.
Serious: the belly is swelling and breathing is fast. Treatment is harder and less likely to work.
Emergency: several fish stop eating at once, or a fish is lying on the bottom with a hugely swollen body. Experts describe bloat as hard to treat once swelling shows, and some estimate that around half of visibly bloated fish have problems no drug can fix.

Bloat can spread through a group, possibly because fish pick at a sick or dead tankmate and its droppings. Treat every fish in the tank as at risk.

What to do right now

Stop feeding the main tank for 2–3 days. Healthy adult cichlids handle this easily, and it rests their guts.
Move the sick fish to a hospital tank: a bare-bottomed tank with a heater, an air stone and a mature sponge filter, filled with water from the main tank. See quarantine.
Test the main tank for ammonia, nitrite, nitrate and pH. Rift-lake cichlids need zero ammonia and nitrite and low nitrate.
Do a 30–50% water change with dechlorinated water at the same temperature.
Remove any dead fish at once so others can't eat them (see dead fish).
Call a vet who treats fish today. Metronidazole is the usual treatment, and many countries, including Canada, the UK and much of Europe, require a vet prescription for it.

What to do next

Medicated food beats medicated water

Metronidazole works best inside the gut, so if the fish is still eating, giving it in food is far more effective than adding it to the water. Your vet will tell you the dose and how long to give it. Ask about making a gel food: the drug is mixed into gelatin with fish food and fed for the full course. Some vets also suggest Epsom salt (magnesium sulfate) as a mild laxative, either in the hospital tank or in food. Follow their numbers; don't guess.

If the fish has already stopped eating, water dosing is the fallback, but it is much less effective. A vet may also add a broad-spectrum antibiotic or a dewormer, because necropsies of bloated fish often find bacteria, the flagellate Hexamita (see Hexamita), worms or other parasites, often more than one at once.

Cautions while treating

Remove activated carbon from the filter while you medicate, or it may take some of the medicine out.
Finish the full course even if the fish starts eating again. Stopping early invites relapse.
Shrimp, snails and plants are rarely in a rift-lake tank, but if you treat a mixed tank, check the label and ask your vet about invertebrate safety.
Plecos, catfish and loaches that share a cichlid tank tolerate metronidazole reasonably well, but watch them closely and don't overdose.
Don't add salt "to harden the water." Table salt doesn't harden water, and some vets suspect it makes bloat more likely.

Bringing the fish back

Once the fish eats normally and passes dark, solid poop, keep it in the hospital tank for another week. Then return it and restart feeding in the main tank with small amounts of a plant-based food.

Products that help

Hospital tank kit (small tank, heater, sponge filter): isolates the sick fish so you can treat and watch it.
Liquid test kit: checks ammonia, nitrite, nitrate and pH; use it before and during treatment.
Vet-prescribed metronidazole: the usual first treatment for bloat, ideally in food.
Unflavoured gelatin: binds medicine into a gel food the fish will eat.
Epsom salt (magnesium sulfate): a mild laxative some vets suggest alongside medicine.
Spirulina-based flakes or pellets: the right everyday food for herbivorous cichlids.

How to prevent it

Feed for what the fish actually eats. Mbuna and Tropheus are grazers with long guts built for algae. Base the diet on spirulina or vegetable flakes and pellets, plus blanched spinach, zucchini (courgette), peas or nori.
Keep rich foods as rare treats. Avoid beef heart and other red meat completely, and limit bloodworms and tubifex. Seriously Fish warns that meaty foods upset these fishes' digestion.
Feed small amounts, more often. Several small meals a day suit grazers better than one big one. See overfeeding.
Keep the water clean and stable. Weekly water changes, zero ammonia and nitrite, and nitrate kept low.
Reduce stress. Overcrowding, constant chasing and frequent rearranging all raise risk. See aggression.
Quarantine new fish for 4–6 weeks before adding them.

Experts disagree on which part of the diet matters most. Many vets and keepers blame too much protein and fat with too little fibre. Others argue that cheap fillers (wheat, corn, rice, soy) are the real problem and protein matters only because rich foods tend to lack roughage. Both camps agree on the answer: plenty of greens and fibre, and no junk.

Why it happened

Bloat usually starts when the gut of a herbivorous cichlid is stressed by the wrong food, poor water or bullying. The normal balance of gut life breaks down, parasites and bacteria multiply, and the gut becomes inflamed and blocked. The swelling you see is the late result of damage that started days earlier.

When to get help

Call a fish vet as soon as you suspect bloat, because the drugs that work usually need a prescription and timing matters. Get help immediately if more than one fish is affected, if fish keep dying, or if you can't get medicine within a day. A vet can also examine a fish that has died (a necropsy) to find out what is going on in the rest of the group.

In the game

Multiple Tank Syndrome doesn't have a Malawi bloat card yet. The Metronidazole card (which saves fish from Hole-in-the-head) and the Lake Malawi 75 tank are the closest relatives.