Malawi Bloat is without a doubt the most prevalent disease afflicting aquarium-kept African Cichlids. Despite its prevalence, little is really understood about this disease. In an effort to understand what the experts are saying about it, I have spent a considerable amount of time researching this topic. What I have learned is that not everyone is in agreement, but there is some consensus about possible causes, responsible pathogens, and even treatment. What appears below is my attempt to represent the majority view. I begin by presenting the most common symptoms of the disease, its course, and then a description of documented possible causes for the onset of this disease. Following this, I conclude by presenting several recommendations for prevention and treatment.
I should begin by saying that Malawi Bloat does not only affect fishes from Lake Malawi but also those from Lake Victoria and especially Lake Tanganyika. While all African Cichlids are susceptible to contracting this deadly disease, those that seem most prone are those whose diet consists primarily of vegetable matter. More on possible causes will be discussed below.
The first symptom is usually a loss of appetite. Other characteristics follow if treatment if not begun at this point. These secondary characteristics include abnormal swelling of the abdomen (hence the name-bloat), an increased respiratory rate, reclusiveness, white streaky feces, and sitting on the bottom of the tank or lingering at the surface. Red marks around your fish's anus or skin ulcerations might also be apparent (as shown in the picture below). Symptoms only appear in the latter stages of the disease; therefore, it is important to begin treatment as soon as symptoms are noticed, otherwise you will most likely lose your fish.
By the time these secondary characteristics appear, extensive damage to the fish's liver, kidneys, and/or swim bladder has probably occurred; therefore, waiting to administer treatment lessens the odds for recovery. After the onset of secondary symptoms, death typically results within 24-72 hours, although I have seen fishes hang on for more than a week in this condition. While it is not unheard of for a fish in this state to recover, I have never successfully recovered a fish already displaying secondary symptoms.
This is where most people tend to disagree when it comes to discussing Bloat. Some say it's bacterial in origin and others contend it's caused by a parasite. Notwithstanding the lack of overall agreement, my review of published material has led me to believe that Bloat is induced by a protozoal parasite in most cases.
Most researchers support the view that this protozoan resides in the intestines of healthy fishes, but can proliferate to harmful numbers under stressful conditions. In larger numbers, this parasite will cause blockage of the intestinal tract. This is probably responsible for the fish's lack of appetite. As the parasite grows in numbers, it becomes invasive, moving beyond the intestine by punching holes in its walls - causing the fish to bloat. Note, fish die from Bloat not because they starve to death, but because of the damage inflicted upon their organs as noted above.
There is also considerable debate as to whether this disease is contagious. My personal feeling is that is. In my experience, Bloat doesn't just claim one victim, but usually three or more. This could be because all of the fish were exposed to the same caustic factor, but I don't think it's that simple. You see, the symptoms don't appear in all the fishes at the same time, but rather sequentially. In other words, fish A doesn't eat on day 1, and on day 2 fish A starts to swell and fish B doesn't eat, and then on day 3 fish B swells and fish C doesn't eat, etc.
Three Main Causes For Bloat
1.) Stress. Stress can be caused by many factors, too many to list here. The most common cause of stress is long-term exposure to poor water conditions. This can be due to infrequent water changes, not enough aeration (for the denitrifying bacteria), and overfeeding. All three of these factors lead to elevated nitrate levels in the water. Fish are very good at fighting off disease on their own, but when exposed to poor water conditions over a long period of time, they become stressed and their immune system does not function at its optimal level (just as with humans!). Other causes of stress may include catching fish, transporting them, water changes, or an insufficient number of hiding places from tankmates.
2.) Salt. The addition of large amounts of salt (NaCl) with the intent of simulating a more natural habitat. True, the rift lakes of Africa are alkaline and have very hard water (pH 8.0-8.9, and a General Hardness between 200-400 ppm), but common salt will not alkalinize your tank. What makes water "hard" is a combination of dissolved calcium and magnesium. If you have soft water and need to raise the pH/hardness of your water, there are several appropriate ways to do this. Homemade buffers are easy and very inexpensive. There are also several quality commercial buffers available, such as SeaChem's Cichlid SaltTM. Crushed coral for substrate or the addition of limestone to your tank is also helpful in raising the pH of aquarium water, but because minerals don't stay suspended in water for long, it's important to do frequent water changes. Using any wood is discouraged, as it will only serve to lower the pH of your water, even if its effects are minimal.
3.) Improper diet. Many cichlids - particularly herbivorous ones - have long intestinal tracts, requiring a relativley longer period of time to digest their food. Consequently, it is quite common for these cichlids to develop intestinal problems. The decomposition of improperly digested, or improperly excreted foods can irritate the intestinal wall, and stress the fish, giving the invasive parasite a foothold. This can often come about when a primarily herbivorous, algae-scraping cichlid (like Tropheus or Pseudotropheus spp.) is fed high protein foods such as bloodworms, or pellet and flake foods containing large quantities of fish meal. Slimy or soft foods, such as brine shrimp, should be avoided and replaced with crunchier foods such as mysis. In light of this information, and experience, it is important to avoid certain foods, and to go light on others. (For a detailed discussion of this topic, see Feeding African Cichlids.)
Once you notice that your fish has lost an appetite for food (and is not just holding fry in her buccal cavity), you should remove it and begin treatment immediately. There are two effective treatments for Bloat that I know of. The first and most common is Metronidazole (Emtryl or Flagyl), and the second is Clout. The treatment should be preceded by a 30% water change (in an effort to improve water conditions) and increased aeration, followed up with a 50% water change. It is also a good idea to remove any biological filters you may be using, even though these drugs claim they don't harm denitrifying bacteria. The initial 30% water change is not necessary if this is a hospital tank not previously in use. The water change is important partially because you won't be performing water changes for the duration of treatment, not to mention the fact that you have just removed a large percentage of your bacteria. Store your filters in some of the water you removed from the tank prior to treatment.
In addition to treating your tank with either one of these drugs, it is also recommended adding an Epsom salt/Table salt mixture to your tank. Mix the two half-and-half, and add a handful of this mixture for every ten gallons of water. Epsom salt is a natural laxative and will help your bloated fish lose some of the water it has been taking on. Epsom salt is very cheap, costing something like $2 for 3 lbs. It can be obtained from any grocery store or pharmacy.
If treating with Metronidazole, add 100 mg (about 1 ½ scoops) for every 10 gallons (or 38 L). Repeat this dosage every two days as required. Fish usually heal (if they survive the disease) within a week. You can typically tell when this occurs because the infected fish will regain its apetite. If, on the other hand, your infected fish has retained its apetite, you can easily administer this drug with its food. In a disposable cup, add some water from the tank, a few fish food pellets, and a single measure of the drug. After the pellets have soaked for a few minutes, pour all of the contents of the cup into the tank. When administering this drug, turn off any UV, ozone, or chemical filtration as these disable the active ingredients of the medication. Following treatment, perform a 50% water change. SeaChemTM and AquatronicsTM both sell drugs containing Metronidazole, the former being called Metronidazole and the latter being called HexamitTM.
Treating Bloat using Clout is also relatively simple. As already mentioned above, before you begin treatment, remove any carbon you might be using in your filters and perform a 30-40% water change. Using a disposable cup, dissolve in some tank water one tablet of Clout per 10 gallons (round up if necessary). Pour the mixture into the tank just a little bit at a time, perhaps taking a half hour to administer a complete dosage -- this drug can be very strong and so it is important to follow this guideline so as not to shock your already stressed fish. Repeat the same dosage for the next two days, again performing a 30-40% water change beforehand. Daily water changes are essential for Clout's maximum effectiveness. The water changes also facilitate the removal of the old, disabled chemicals. Three days of treatment should be sufficient if the inflammation is not too severe, otherwise treat for a full five days. If after five days, you still don't notice a change, then resume treatment again after a two day hiatus. Once you have concluded the treatment, perform a final water change 24 hours after the last dosage.
Both drugs are effective at stopping the spread of Bloat in the tank. CloutTM is a very strong drug that was developed particularly for fish. Most other fish medications have human counterparts including Metronidazole. In my experience, Metronidazole has only been effective at stopping the spread of the disease and not at curing fish already displaying symptoms. CloutTM, on the other hand, has proven somewhat more effective at curing bloated fish. I should warn you, however, that CloutTM will turn the water blue and stain the silicone in your tank, as well as any airline tubing you may have. If you are not careful with it, it will stain anything else it comes in contact with. While it has proven effective for me, I wish I had know what it was going to do to my tank. I still would have used it knowing this, but I just felt gypped afterward. And so, I am just alerting you.
Additional note: When using these or any other medications, it is a good idea not to turn on your hood lights while treating your fish. These two drugs don't have any active ingredients that are disabled by UV rays like many antibiotics, notwithstanding, the dark atmosphere will help your fish to relax and recuperate.
Metronidazole works better at elevated temperatures (e.g., 80°F), but aeration should be increased because the O2 content of water decreases with higher temperatures. Elevating the temperature of the water can be beneficial also because it increases the fish's metabolism and heightens its immune response, while also hastening the life cycle of the parasite, thereby shortening the time required to cure the fish. □