It is very important that once it is identified you act quickly. The most apparent sign is that your fish begins to look bloated (hence the name) and an overall lethargy to the fish. Another more precise symptom is white streaky feces.
There is a lot of disagreement on what actually causes Malawi bloat. It used to be thought that it only affected African fish from Lake Malawi and Victoria. But it affects all fish and cichlids seem to be more susceptible to this disease. I have found 3 separate possible causes of Malawi bloat; parasites, bacteria or over feeding. Basically no one knows for sure.
To treat this disease the very first thing you should do is separate the fish from the rest of the aquarium in a quarantine tank. If caught early enough a fish can make a full recovery. You will want to treat the infected fish with either Clout or Metronidazole. Both are easily found at your local pet store.