Bloat In Fish: Causes, Treatment, And Prevention

Finding a bloated fish in your tank?

So your find a bloated fish in your tank and begin to wonder what’s wrong? Next you consult Vet Google and find an number of equally scare articles. What is it? Is it dropsy or bloat? Constipation or obesity? And what happens so often with Google its hard to differentiate the difference.

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Difference between Bloating and Dropsy in a Discus


Bloat is a pretty straightforward illness. It does exactly what it says on the label. The prime symptom is, obviously, that they’re bloated!

But when we look at some other symptoms, we can narrow down the cause of the bloat, which will help us when we go to treat it.

  • Excessively (unnaturally) large abdomen
  • Loss of appetite
  • Loss of interest in swimming
  • Scales standing up on end (“pine coning”)
  • Curved spine
  • Ulcers
  • Redness of skin or fins



Causes of Bloat

Bloat has a handful of common causes, and I’ll get to those in a second. For now, let’s figure out what causes this, shall we?

Treating Bloat

The first step in treatment, unless you have an excellent reason not to – and I mean really good! – is to quarantine the sick fish to prevent it from spreading. If your other fish are infected or they’re the only fish in the tank, take the following steps as “first treatment”:

Do a water change:

Unless you just did a significant water change (today), your first step should be to do a 50% water change. Make sure to add de-chlorinator and a little bit of aquarium salt (1 tablespoon for every five gallons.) If you usually add salt, go about your usual business.

Reduce stress:

Dim the lights or, even better, turn them off. Remove critters that are harassing sick fish. And stop pressing your face to the glass to make sure they’re okay.

If your fish is struggling to breathe, putting them in a breeder box close to the surface will help.

Stop feeding your fish:

This may sound counter-intuitive, I understand.

But feeding your fish now will only make matters worse. They probably won’t eat it anyway. Your fish will be okay for at least three days without food. This timeframe should be long enough to start making some progress, and you can resume feeding again when they’re better.

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Bloat From Internal Bacterial Infection

The consensus is that when fish develop bloat due to bacterial infection, it’s usually a gram-negative bacteria. Problem is, once they develop an internal infection, their whole system gets messed up.

Fish have a complex digestive system full of bacteria and microfauna. Much like humans.

Once this system is under stress, it gets out of whack, once it’s out of whack, the fish’s immune system drops, sending this gut system into further chaos and repeating the cycle.

Additional Syptoms

bulging eye
Bulging Eye
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Treatment can, providing this is the issue, be done with a gram-negative anti-bacterial. I like Erythromycin for general antibacterial and Doxycycline for gram-negative if you find that Erythromycin isn’t working.

Erythromycin is usually used for treating gram-positive, but can be used for gram-negative also.


If the fish is already experiencing bacterial issues, their digestive system is out of whack. Adding an antibacterial will inevitably worsen the out-of-whack-ness. Which has wide-reaching implications. Treatment may make things worse, but they’re unlikely to become better without treatment.

Bloat From Viral Or Protozoan Infection

Several viral diseases can cause bloating. DGIV is one of them, but it’s far from the only one.

In this case, bloating is a secondary illness that was created by the first. To treat this type of bloat, you have to diagnose the primary disease accurately and treat that first.

With protozoans, bloat becomes easier to treat but harder to diagnose.

Additional Symptoms


Alas, this is a hard one. If it’s something like DGIV, there is no treatment. If it’s another viral infection, you’d need to diagnose that first to find the cure.

In the case of protozoan infections, that’s a bit easier: salt dip is usually the answer.

Dissolve four teaspoons of aquarium salt per gallon in a bucket. Place the fish in the bucket and monitor for signs of stress. Well, more stress, anyway.

Keep them in this solution for 30 minutes and place them back into the tank. If the fish appears to “roll over,” you should remove them as quickly as possible and put them back in freshwater.

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Freshwater fish don’t like salt. No surprise there. Also research weather the species is sensitive to salt. Make sure you totally dissolve the salt.

Additionally, the stress of plopping them in salt – when they’re already sick – could further weaken their immune system. Provided it’s a protozoan you’re treating. If you’re dealing with something else, diagnosing may be difficult.

Bloat From Incorrect Care (Malawi Bloat)

Bloat Montage 1

Malawi bloat is most common in African cichlids. But this isn’t to say “Malawi bloat” can only impact African cichlids.

Improper care can give nearly any fish bloat. Herbivores who are fed foods high in protein and fats are especially susceptible to this version of bloat.

But we know three things invariably lead to it; incorrect diet, poor water quality, and misuse of salt in routine water changes.

Bloat 3

Additional Symptoms


In the long term, obviously, correct whatever went wrong.

If it’s from food, stop feeding them foods that are so high in protein. If you’re unsure if your food had more meat proteins or plant, take to Google with the ingredients list on your fish food. Additionally, check the best by date on your fish food. If it’s bad, that’s likely the cause.

If food was the culprit, you’re likely dealing with an internal infection.

Again, I like Erythromycin for general antibacterial and Doxycycline for gram-negative if you find that Erythromycin isn’t working.

For other conditions that may be at play, like water conditions, you’ll need to do research on your species and check against your water chemistry. It’s best if you can get them into moderately okay conditions first and then transition them into ideals if pH, temperature, or salt use is the issue.

Changing those conditions too fast will shock them.


We don’t understand Malawi bloat all that well. So we don’t know how to treat it all that well either.


Bloat From Hexamita (HITH)

Hexamita is probably best known for causing hole in the head (HITH) and lateral line erosion (HLLE) in cichlids. Most of the time, there are no symptoms that it’s there until your fish’s face has been getting nibbled and gnawed at for who knows how long? This lack of outward signs is what makes this so hard to diagnose.

Additional Symptoms


I hate to be the bearer of bad news here, but there is no official treatment of bloat caused by hexamita. The best you can do is follow the direction at the beginning of the treatment section (quarantine, water change, reduce stress, do not feed) and wait it out. You can attempt to treat with metronidazole, which is available over the counter in the states as of late, but it may need to be prescribed if you’re elsewhere.


In advanced stages treatment may not work, prognosis for fish not good.


Obesity, overeating, and getting chunky aren’t the same as bloat. But, for most people, when they think bloated fish they think their abdomen is large. And, admittedly, it’s hard to tell the difference between a fat fish and one that’s bloated by looks alone.

So, for the sake of inclusion, here’s my say on overfeeding.

Additional Syptoms


Feed less. It’s as easy as that. But monitor it to see if the condition prolongs and or develops further into something diagnosable.


Beware it could develop into an actual medical condition and it wasn’t simply over eating.


Constipated fish are a common cause of “bloat” – although not bloat itself – the condition can lead to a bacterial infection and cause actual bloat.

Additional Symptoms


Most people will tell you to feed peas – and this works – provided your fish will eat peas. If your fish isn’t interested in peas, the primary goal is to give them fiber or “roughage” to pass the block. In my experience, baby brine shrimp and daphnia will always get the job done – live being the best if you can. If you can’t, frozen will work too.

“Classic” Dropsy

Dropsy is more commonly said when a fish’s scales begin to “pinecone out” due to the excessive internal pressure from the fluids. You can usually see this best from above. Dropsy isn’t often it’s a separate category of bloat – it’s always caused by one of the above issues.

So why is it here? Because there’s a stage of bloat where it’s gone past the point of being curable – and that’s “classic” dropsy. At this point in the game, there’s usually some severe damage to the kidneys that’s irreversible.

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Addition Symptoms


The general consensus is that once bloat has progressed to this level, it’s not treatable. And I would agree with that statement. Due to the damage that’s been done to the fish’s kidneys at this stage, even if you managed to get the bloating under control, they would likely succumb to kidney failure.


“Classic” dropsy is usually caused by a highly viral microbe that attacks the fish’s kidneys. There is currently no known cure for this. 

Preventing Bloat

In general, a lack of stress, clean water, and a proper diet go a long way in preventing these illnesses. In some cases, your fish food could’ve gone bad.  This can easily cause internal bacterial infections and happens more often than you might think. Improper tank mates, bad water, and a host of other things put unnecessary stress on the fish as well. 

Good fish keeping hygiene will usually, though not always, prevent bloat. 

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