Bloat In Fish: Causes, Treatment, And Prevention

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Flipping on the tank lights to be greeted with a big bobbing pine cone of a fish is undoubtedly alarming. Take to Google, and the panic starts to mount. What is it? Is it dropsy or bloat? Constipation or obesity? Do I treat with salt or mediation? Is it fatal or… you get it. You probably get it because you tried this.

Here are some simple truths: abdominal swelling is caused by fluid build-up in the body cavity, this is bloat or dropsy – although they may or may not be the same thing. And, beyond that, there are eight common causes of bloat – though this is by no means a definitive list. So treatment for bloat, if it’s the sort that you can treat at all, is hit or miss.

Not the sunny side of the news, but it’s the truth. I’ll try to cover all the common causes and treatments of various types of bloat. Hopefully, it’ll shed some more light on the problem for you. So we’ll need to work together on this one: me providing information, you doing the diagnosing to figure out the proper treatment.

Are we good on those terms? Alright. Let’s go then.

Disclosure: If you choose to buy a product I recommend – at best – I’ll make some coffee money at no additional cost to you. I work hard to make sure I’m recommending products you’ll love and that I’m not in your face about my suggestions. If you don’t love it, let me know!

Bloat in fish

Bloat Symptoms

Bloat is a pretty straightforward sounding illness; it does what it says on the label. The prime symptom is, obviously, that they’re bloated! But when we look at some other specifics, we can narrow down the prime suspects for the cause of the bloat, which will help us when we go to treat:

  • 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

Bloat Causes

Bloat has a handful of common causes, each has its own course of treatment – and I’ll get to those in a second – but for now, let’s figure out what causes this, shall we?

  • Internal bacterial infection
  • Viral or protozoan infection
  • Incorrect environment and “Malawi bloat”
  • Hexamita (HITH)
  • Overfeeding
  • Constipation
  • Eggbound
  • True dropsy

Treating Bloat

I’ll break down the treatment of bloat based on the causes. 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 on the tank. 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 turn them off if you can, remove critters that are harassing sick fish, and don’t keep pressing your face up to the glass every five seconds to make sure they’re alright. If your fish is struggling to breathe, putting them in a breeder box close to the surface will help reduce some of their stress.

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.

Bloat From Internal Bacterial Infection

internal bacterial infection

The consensus is that when fish develop bloat due to bacterial infection, it’s usually a gram-negative bacteria at play. 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, not unlike 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 Symptoms:

  • Bulging eyes
  • Protruding scales
  • Red gills
  • Red streaks on body
  • Rapid gill movement
  • Excessive slime coat/mucus production


Treatment can, providing this is the issue, be done with a gram-negative anti-bacterial with varying degrees of success. I like Erythromycin for general antibacterial (though most effective on gram-positive), and Doxycycline for gram-negative if you find that Erythromycin isn’t working.


If the fish is already experiencing bacterial issues, their digestive system is out of whack. Adding an antibacterial will inevitably worsen their digestive system – 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:

  • Curved spine
  • Itchiness (some)
  • Red skin or patches
  • Symptoms that seem unrelated to excess fluid build-up


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 than they’re currently showing, 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.


Freshwater fish don’t like salt, no surprises there. 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)

Malawi bloat is most common in African cichlids, and it’s incredibly obscure. But this isn’t to say “Malawi bloat” can only impact African cichlids.

To the contrary, 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.

Additional Symptoms:

  • White feces
  • Bloody ulcers on skin


In the long term, obviously, stop feeding them foods that are so high in proteins and fats and move to a plant-based diet. If you’re unsure if your food had more meat proteins or plant, take to Google with the ingredients list on your fish food. It’s likely that if this is the cause, it’s an internal bacterial infection at play here.

Again, I like Erythromycin for general antibacterial (though most effective on gram-positve), 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 too fast will shock them.


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

Bloat From Hexamita (HITH)

(HITH) Hole in the head

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:

  • Holes in the head
  • Holes in the lateral line of your fish
  • Sometimes no other symptoms other than bloat


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.


We don’t know how to treat hexamita or how to diagnose it before it becomes advanced.


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 Symptoms:

  • They eat fine (too well, really)
  • No problems with swimming
  • No loss of color


Feed less. It’s as easy as that. You don’t want to put your fish on a crash diet, and I’m partial to chubby fish myself, so I get it. But once it gets to the point where you’re questioning if it’s a medical condition, it’s gone too far.


None, really, other than overcoming your desire to overfeed fish.


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:

  • Stringy feces
  • Pale feces
  • Slimy feces
  • Excessively long trails of poo


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.


The trick is to feed them just enough to get what they need, no more, no less. Don’t offer them anything other than peas, baby brine, or daphnia until they’re better again. You may have trouble sourcing the latter two, especially live, if you didn’t already have them.

Give it a few days, and it’ll usually work itself out.

Egg Bound

egg bound

Few and far between fish become egg bound in the reptilian sense, as in they’ll die if you don’t do something. It’s more term that’s used to describe a female fish with a lot of eggs. These fish tend to look, for lack of better phrasing, “chesty.” When viewed from above they’ll look – to me – great-white-shark-shaped.

Of course, your fish has to be a female for this to be the cause.

Additional Symptoms:

  • Eating fine
  • Swimming fine
  • Seems really healthy


There’s no need to do anything. If you want to breed fish, now would be as good a time as any since you have a fish ready to go. If not, no need to worry, they’ll be fine.


Being egg bound can cause issues if the fish don’t expel the eggs on their own and you continue to take such good care of them. Usually, at some point, they’ll attempt to spawn if exposed to a male, drop, or reabsorb the eggs. This condition seems to impact bettas females and other females that are frequently separated from males for extended periods of time.

“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.

Additional Symptoms:

  • Pineconing


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. 

Further Reading & Resources