Bloat - Causes - Cures - and BIG Myths


Gold Tier VIP
MFK Member
May 9, 2007
Northwest Canada
There seems to be a lot of confusion with regards to bloat, and how it can effect various species of cichlids.

Hopefully the info below will help clarify some of the common misconceptions surrounding this condition.


Protein in & of itself does not cause bloat. Most excess amino acids are excreted - even by fish classified as strict herbivores, and while excessive amounts of protein can put extra stress on a fishes liver, as those excess amino acids have to be deaminated by the liver before they are excreted, this process does not cause bloat. Excessive amounts of protein can also lead to fat accumulation in the liver, and over time can cause serious health issues, even death in extreme cases - but again, this does not cause "bloat".

The whole protein causes bloat thing is nothing more than a myth that has been perpetuated in this hobby by those that don't have a clear understanding of how a fish assimilates protein. The only time that I limit protein intake is when the fish begins to gain size. Then I shift them over to more of a maintenance diet, just as one would with a puppy as they begin to mature. Young fry & juvies have high metabolic rates, which require high energy fuel on a constant basis. If you limit that, you will limit growth. Hence feeding a high volume of "greens" to a juvenile fish known to be prone to bloat isn't the answer at all.

Having said that, excessive overfeeding of any food can on its own cause blockage, and constipation, and the end result is also a "bloat" like condition.

IMO the vast majority of bloat cases have little or nothing to do with the diet. One does NOT want to limit amino acid (protein) intake with a fry/juvenile. To do so will simply limit growth & overall health in the fish. But that doesn't mean that you feed your fish until it's abdomen is extended like a balloon!

I have raised some of the most bloat prone species of fish on the planet (Tropheus sp., Tropheops macrophthalmus, etc) on diets of 50% protein, 10% fat (fry & small juvies), and never lost a fish to bloat.

Pellets Cause Bloat?

I have personally kept numerous species of African cichlids, pretty much all of the species that are considered by the masses to be bloat prone magnets, such as various Tropheus sp., Tanganicodus irsacae, Tropheops Macrophthalmus, P. demasoni, Labeotropheus fuelleborni, Labeotropheus trewavasae, several species of Melanochromis & Metriaclima as well as numerous other species of mbuna classified as herbivores, and over a span of 15+ years in keeping mbuna never once encountered bloat in any of my tanks. All raised on pellets.

The largest producers of African cichlids in the world, all feed pellets, and some of these commercial breeders have been in this game longer than many of the members here have been alive. A past collector and exporter on Lake Tanganyika that I used to converse with (Mark Young) - and who specialized in Tropheus, never once encountered bloat in any of the 10's of thousands of Tropheus that he collected while he was in the biz. According to Mark, the key to preventing dietary stress, was to not overfeed the fish. No overfeeding, no problems.

A Tropheus breeder here in town has probably maintained more tropehus tanks & species of tropheus than many will ever see in one room, and he also fed a premium pellet food, and in over a decade of breeding tropheus, and producing thousands of fry, he never once had any bloat issues in any of his colonies. At that time he was keeping & breeding Kambwimba Red Rainbow, Ilangi, Bembas, Duboisi Maswa, Ikola Kaiser, Kiriza Kaiser II, and Bulu Point cherry spots, and a few others I don't recall. All wild caught fish.

For the various species of mbuna, tropheus, etc, and ideal pellet size for semi-adult - adult fish is 1mm.

When changing diets, feed sparingly for several days which allows the fish gastrointestinal system to adjust to the new food.

If/when bloat is caused by diet, it's often the result of fish being overfed by MASSIVE amounts, and/or using a food that contains a large inclusion rate of terrestrial based grains & grain byproducts. In the case of the latter, high grain content is known to cause intestinal blockage due to its poor digestibility, which in turn results in "bloat". If/when diet is the cause of bloat the trigger is typically caused by poor quality ingredients that the fish has difficulty digesting. (usually cheap grain fillers) If a fish can't digest the food, then it can lead to impactions in the gut. The fish stops eating (as it can't pass what's already in it) the impacted area goes septic from multiplying bacteria, and the result can be (and quite often is) deadly.

If someone is allowing their fish to feed until they are stuffed to the gills, then that becomes a case of operator error, not feed problems. The fact is, many hobbyists do tend to overfeed. To date I do not believe that there is a single food that has been created, manufactured & otherwise that has not been blamed for bloat in someone's fish. I've seen & read it all over the years, yet 100's of thousands of other hobbyists feed these same foods with no issues. Hmmmmm.

When feeding low cost generic foods with excessive grain content, if too much is consumed at once these types of feeds can indeed cause serious gastrointestinal issues in some species, such as those that are prone to bloat.

Also, there is a BIG difference between terrestrial based plant matter (such as soybeans, corn, wheat middlings etc) and plant matter from aquatic sources, such as algae meal, spirulina, and various micro-algae. The former is what many hobbyists have come to refer as "cheap fillers".

For decades Tropheus keepers felt that due to the intestinal length & long digestive process in that species, it should only be fed low protein "green" food, and that any amount of animal based protein could cause bloat. Yet science has proven that in captive bred species of Tropheus the intestinal length can be half of what's found in wild specimens.

"Intestinal prolongation, although indicative of specialization on diets with low nutritional value, such as those of epilithic algae and detritus, has been shown to be highly plastic (Sturmbauer et al.1992). In Tropheus moorii the intestinal length of domestic fish measured only 50% of the length found in wild individuals (Sturmbauer et al. 1992)."

A more recent study that was published in 2009 demonstrates just how great intestinal plasticity can be in response to the diet quality of various species of fish found in Lake Tanganyika.

The above paper clearly demonstrates just how adaptive wild Rift Lake cichlids can be when it comes to their diet. As long as one feeds a quality food, diet will generally be a non issue, and will not cause any type of major gastrointestinal stress. These fish were born to adapt.

Intestinal Parasites

Most authorities on this subject now agree that it's intestinal flagellates that typically cause "bloat" conditions in fish, and most certainly not excess protein, or feeding pellet food.

I think that it's important to understand that "bloat" is a symptom of a disease, not a disease on its own. Intestinal flagellates are common in most freshwater species, and typically these intestinal parasites will not have any serious affect on their host. But, place that same fish under enough stress, enough to weaken its immune system, and within the blink of an eye those same parasites can multiply to numbers that the fish simply can't cope with. If/when those numbers reach epidemic proportions, they can & often will cause damage to the intestinal tract of a fish, and in severe/advanced cases their organs, eventually creating what is commonly referred to as "bloat".

In a healthy fish S. vortens is commonly found in the flagellated stage in the lumen of the upper intestine where it is controlled by the immune system of the fish. In a stressed fish, the immune system becomes compromised, and these flagellates multiply unchecked causing serious localized damage. Once the damage is severe enough the intestinal lining is penetrated and the flagellates enter the blood stream causing systemic and organ infections, failure, and ultimately death of the fish.

There are many other stress factors that can take place in a glass tank, and it is typically those stress factors that trigger an outbreak of internal pathogens, usually Spironucleus vortens, that ultimately result in bloat conditions.

Hexamita Intestinalis is another catch all term to describe the various protozoa that trigger bloat conditions in tropical fish. In the vast majority of cases, those where clinical studies have identified the actual flagellates involved (specifically in cichlids), it has been Spironucleus vortens, not Hexamita or Octomitus species as previously believed. While it appears that much of the earlier identifications in ornamental species of fish may be erroneous, the overall treatment is pretty much identical. Some detailed reading on the subject of treating these flagellates in a very safe, cheap, & effective manner can be found in the link below.

As stated previously, IMO the vast majority of bloat cases involving cichlids has nothing to do with the diet, but with other stressful factors, such as aggression from tank mates, lack of shelter, water quality such as dissolved organic compound levels, 02 levels, etc-etc., which in turn can cause a 'normal' amount of intestinal pathogens to proliferate to harmful numbers. In some cases it may be nothing more than survival of the fittest, which is what takes place in wild every day. A fish with a weak immune system will obviously be the first fish to succumb to illness if/when stress becomes a factor, no matter what you feed them.

A classic example of how/why bloat can take place in a tank of juvenile fish; In an attempt to get massive (monster) gains a hobbyist power feeds their juvenile fish, in doing so bacteria, organic waste, etc builds up quickly in the system, and as fish gain size stress levels in the tank increase from aggression/hierarchy issues. Also as the fry begin to gain size over a few months sometimes those massive regular water changes begin to slide, and now you have a breeding ground of bacteria, and stress levels that are climbing every day. The perfect scenario for an outbreak of spironucleus aka bloat.

The direct cause of the bloat wasn't the food, it was a case of operator error. Feeding fish is part art, and part science, feed a high quality easily digestible food, throw as much clean water at your fish as humanly possible, and keep them in an overall stress free environment and bloat will usually become a non issue.

IMO almost all ailments in fish are triggered by stress, and one needs to learn early on what each set ups limitations are. If/when we attempt to go beyond those limitations, we risk the health of everything within our system. Some hobbyists seem to learn this straight away, others never seem to catch on & when things go south they look for something to blame instead of taking responsibility for their own actions. Human nature I guess. Most experienced beani keepers will recommend that this species does best on its own, just as many other cichlid species that are bloat magnets. Generally speaking these species do not do well (long term) in community settings as there is always a struggle for hierarchy within the tank. This constant struggle for dominance causes stress, and often this stress eventually triggers bloat in species that are more sensitive to this condition. The same applies to species such as Tropheus, that establish a hierarchy within the colony & once that hierarchy is established sometimes simply adding "a few more fish" will cause the entire colony to come under major stress while new positions in dominance are being established.

Species such as Tropheus are definitely not beginner fish, they can be nasty pieces of work and if by the luck of the draw you end up with too many dominant males, or some smaller weaker specimens, the stress from aggression can end up triggering bloat within the colony. Having said that, IME if one follows a few basic rules they can be as easy as keeping any other species of cichlids.

The secret to keeping Tropheus successfully is as follows.

1. The larger the tank the better.

When conversing with Mark Young (at that time a collector & exporter living on the shores of Lake Tanganyika) he told me that in his experience dominant males would stop chasing at the 6-8ft mark, so he built all of his concrete vats 12 ft. End of serious aggression problems.

2. The more fish that you can accommodate in your tank the better, it helps spread aggression so that no one fish is ever singled out and chased or harassed relentlessly.

Mark kept hundreds of tropheus together in his 12 ft vats, but they also held several hundred gallons of water.

3. Massive water changes on a regular basis, and high levels of 02 at all times.

These fish are found in the surf zone, where there is lots of current & high 02 levels. If you don't like water changes, pass on tropheus, as the more fresh water that you can throw at them the better. Even in Mark's massive tanks he had a constant 24/7 flow of water being exported out of the bottom, and a constant 24/7 flow of fresh water coming in.

4. The less territory there is for dom males to fight over, the better.

While not many people like bare tanks with no rock work, with tropheus less = more. Mark's large vats were typically void of any type of structure that a dom male might claim as being his. Sometimes he would add a few boulders when adding a new group of wild fish just to help calm them, once the fish settled in then out the rocks came.

5. Keep the diet simple, feed small amounts 2-3 times a day, vs one big meal a day.

The more that you deviate from the above, the more risk you will have in stressing out your fish, and potentially having them come down with bloat. Sometimes you can push the envelope and it's all good, and sometimes it can end up in disaster.

Below is a photo of one of Mark's tropheus "tanks", at the shore of Lake Tanganyika in Mpulungu, Zambia.

Sometimes when these "bloat" ailments surface it seems to appear that there is no reason at all. IMO the reason for this is due to the fact that all fish are individuals, and while they can have individual behaviors & temperaments, I also believe that each fish can only tolerate individual levels of stress before they weaken enough to become susceptible to these stressors. You'll typically find that the same holds true for most organisms on our planet, including humans.

Just as one can have genetic runts, I also believe that one can end up with fish that have genetically weak immune systems, or at least weaker than normal. This would explain why one fish in a tank full of (any species), can end up with fungus, or pop eye, or HITH, or whatever, while other fish in the same tank have no health issues whatsoever. Or why some fish survive an ammonia spike, while others drop like flies. Or why only one female in a tank full of breeders ends up egg bound, while no other females ever exhibit this problem. IMO the same applies to bloat.

In the wild Mother Nature has a way of dealing with fish such as this, but what if some of these fish are collected, and exported? How many people cull WC fish? Most breeders will do almost anything to save a prized egg bound female, yet in the wild that fish would either pull through on its own, or else .....

Overuse of medication can also cause an immune system to become severely compromised. Many exporters & importers dose the fish with meds shortly after they are collected or received, again with tranqs when the fish are shipped, while many hobbyists dose the fish yet again with meds when they arrive to their new home. (as a precautionary step) Already the fish have the odds stacked against them, and all it takes is one single weak link to start a snowball effect in ones tank.

Perhaps in some cases, even when we do everything right, it ultimately all boils down to nothing more than a roll of the dice with certain individual fish.

While I have posted the following link a number of times on MFK, I'm guessing most people haven't taken the time to read this entire paper. It's a long read (200+ pages) but well worth the time for anyone that wants to really understand what the root cause is for most cases of "bloat" in cichlids.

I've taken the time to compile some key portions of this paper which should help explain how bloat comes about, exactly what causes it in ornamental warm water tropical species of fish, and how young fish are more susceptible to severe cases of bloat vs larger fish.

"In freshwater fish, Spironucleus sp. has been reported in cichlids, including angelfish, and cyprinids. Spironucleus elegans has been found causing disease in angelfish (Pterophyllum scalare) in Europe (Kulda and Lom, 1964b), while Spironucleus vortens has been also reported from the intestinal lumen of angelfish bred in Florida (Poynton et al., 1995). They can be found in the intestinal tracts of healthy fish and they may invade the body of the host and are capable of causing severe parasitemia under stress conditions (Molnár, 1974).

Hexamita are considered commensal organisms but can be pathogenic under various stressful conditions such as nutritional inadequacies, suboptimal water quality, crowding, poor sanitation and infections from other pathogens or parasites (Specht et al., 1989; Uzmann et al., 1965)

Although Hexamita and Spironucleus cause disease in several economically important fish species in many regions of the world, their pathogenicity is not well known (Woo and Poynton, 1995). It has been believed that the effects and the severity of diplomonad infection are dependent on fish size, tissue site infested, environmental conditions, stocking density, season and stress factors (Allison, 1963; Buchmann and Uldal, 1996; Mo et al., 1990; Uldal and Buchmann, 1996). Fish infected with Hexamita salmonis exhibited clinical signs correlated to their body length and weight (Uldal and Buchmann, 1996). This supports the study of Allison (1963) that large trout, more than 3 or 4 inches long, showed a smaller effect from Hexamita infection than smaller trout.

It is believed that the organisms invade the intestinal epithelium and disseminate to other tissues when the host’s resistance has been suppressed (Woo and Poynton, 1995). It has been suggested that only Spironucleus spp. cause systemic infection because they can invade intestinal mucosa and disseminate to other tissues (Siddall et al., 1992). Evidence of systemic spironucleosis was reported in cyprinids and aquarium fishes (Molnár, 1974), and in salmonids (Mo et al., 1990; Poppe et al., 1992; Sterud et al., 1997).

It has been suggested that only Spironucleus spp. cause systemic infection because they can invade intestinal mucosa and disseminate to other tissues (Siddall et al., 1992). Evidence of systemic spironucleosis was reported in cyprinids and aquarium fishes (Molnár, 1974), and in salmonids (Mo et al., 1990; Poppe et al., 1992; Sterud et al., 1997). In cyprinids, many Spironucleus sp. were found in the gut where they caused reddening of the mucous membrane, brownish-gray discoloration and necrosis of liver, and haemorrhagic enteritis. In aquarium fishes, the parasite has been reported to cause losses in angelfish stock of up to 50% of the population. The infected fishes showed reddening of the skin, and haemorrhages and ulcerations in the region of the head (Molnár, 1974). The parasites were found in the gut, gallbladder and visceral organs. Spironucleus sp. were also found in large numbers in the blood and the muscle of infected fish."

From this paper we know that these parasitic protozoa can be found in the intestinal tracts of healthy fish. We also know that STRESS, which weakens a fishes immune system, allows these flagellates to multiply in numbers to the point of causing systemic infections, which left unchecked will typically result in the death of the fish.

This paper supplies the most in-depth research that I think one can currently find on this subject, and is well worth the read for anyone that wants to better understand "bloat", beyond what you will typically read on the various fish forum chat rooms.

My apologies for being long winded in this post, but this is a topic that seems to repeat itself on a weekly basis on this forum & many others, especially the connection between bloat & protein. There is absolutely no credible evidence to suggest that protein causes bloat in any species of fish, unless that protein is from low quality sources that are difficult for certain fish to digest. The notion that protein is to blame goes back 25+ years ago when most commercial foods did in fact contain vast amounts of terrestrial based grains, which did in fact cause gastrointestinal issues (especially when overfed) in some species of fish. Unfortunately this outdated misconception still lingers in the hobby today.



Feeder Fish
MFK Member
Oct 31, 2011
Very well written, clearly a lot of thought and effort went into this and it is appreciated.


Gold Tier VIP
MFK Member
May 9, 2007
Northwest Canada
Thanks. I know that it's a long read but hopefully some of that info will be applied by fellow members & it will help prevent some future bloat outbreaks.


MFK Member
Sep 28, 2009
Gatihersburg, MD
Thank you so much for taking the time to write that article. I thought that I knew a thing or two about bloat, but you just expanded my knowledge immensely.



Gold Tier VIP
MFK Member
May 9, 2007
Northwest Canada
No problem, glad to help, Tony.


Feeder Fish
Dec 30, 2011
Airdrie Alberta, Canada
very good. I now know that I have been overfeeding my oscar. and stress. but in your article you say privacy is important and less decoration is more. (less to claim and fight over) Can I give my Oscar more privacy with less? set up walls maybe? or a den?


Jack Dempsey
MFK Member
Apr 4, 2012
Nha Trang, Vietnam
Thank you for taking the time to post all that! Pablo?

I've, for a long time never understood the whole "pellets cause bloat" theory and speaking with Mark over the years as well as the countless amounts of hobbyist willing to try something new there was less and less credibility to it.