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Bloated Betta Fish | Mystery Bloat

Updated on December 13, 2009

Every now and again, a Betta fish will become mysteriously bloated. The owner will usually believe that the fish is constipated and, following well meaning advice, will fast the fish and give it little pieces of cooked pea. At some point, the owner will realize that the fish is still bloated, but pooping normally, and then start to become worried.

'Mystery Bloat', a condition so named because nobody in the fish keeping community, from experts to veterinarians, seems to understand what causes it, is a cause of much suffering for betta fish and their owners.

Many people incorrectly diagnose 'Mystery Bloat' as being a case of dropsy. On its own, it is not, although it seems to sometimes become dropsy in the later stages of its progression. Dropsy, for the uninitiated, is a condition in which liquid fills the body of the fish, causing scales to stick out in a pine cone fashion. By itself, dropsy is not an ailment, but rather a symptom of an ailment. Fish with dropsy become lethargic, stop eating and eventually die.

Mystery Bloat, on the other hand, manifests quite differently. Mystery bloat occurs largely on the underside of the fish. The bloated fish will not stop eating, or indeed, appear to be ill behaviorally. It will continue to swim about, blow bubble nests and eat happily until it succumbs to the condition.

Mystery bloat appears to be a largely fatal condition, and effective treatments for it are unknown. Some people recommend Epsom Salt baths, to help draw the excess liquid out from the fishes' body, and others recommend broad spectrum antibiotics to kill any bacterial cause. The truth of the matter is however, that at the time of writing, bettas have been dying for decades as a result of mystery bloat and nobody really knows why. The cause could be viral, it could be bacterial, or it could be caused by some other agent that remains, as the title suggests, a mystery.

So what can you do if your fish has Mystery Bloat? Well, for one, isolate it and ensure that it has very clean water. Adding aquarium salt is not recommended, as it may cause problems for a fish already unable to eliminate salt from its swollen body, but a small amount of Epsom Salts may help. Epsom salts can be given in the form of a bath at higher concentrations of  1 Tbsp per gallon, or they can be added to the tank water at a concentration of 1/8 tsp per 5 gallons.

You can also try feeding medicated food, but ensure that the medicated food is treated with a broad spectrum antibiotic.

The frustrating thing about Mystery Bloat is that these treatments may help a great deal or not at all. The best thing you can do for your fish at this time is make him as comfortable as possible,  provide what treatment you can, and be prepared to humanely euthanize him if he starts to show signs of obvious suffering.

The most human way to euthanize a betta is to use half a small bottle of pure clove oil in a small container of tank water. Shake it well to make the oil emulsify throughout the water, then add the fish. Clove oil will put the fish to sleep almost instantly, though you should be aware that fish can revive from clove oil, so leave the fish in the solution until it is quite obviously dead. If you are in any way unsure if it is dead or not, leave it for 24 hours, after which point, it is most certainly departed.


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      jas 3 years ago

      clove oil is the best, quickest way

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      bobba 4 years ago

      The easiest, most fishane way to euthanize your Betta, or most any pet fish, is to leave it on the bathroom counter for a couple hours, then flush it down the toilet.

      Simple and straight forward.


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      KD 5 years ago

      Okay, most vets I know do not treat fish. It can be scary to have to euthanize a fish and is best left till you know the animal is going to die (not just suffering).

      It's not a great solution and really it's best to try and treat the fish, but if you can see the fish is suffering and whatever it is sick with is fatal then driving around looking for a fish vet is a bit crazy. Sure you want to be sure the animal dies painlessly, but there is no need to get a vet involved unless you already know one who can analyze the situation.

      Ben, betta splendens are not dangerous for humans and females often live together. The males battle for the right to breed and must be kept separate- that is why they are fighting fish.

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      Kyle 5 years ago

      I have to agree with Emily. Ben, you are a moron.

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      Emily 6 years ago

      Ben- you are a moron. That is all.

    • profile image

      Ben 6 years ago


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      cherie 7 years ago

      i love your work !

      I have spent all night printing & reading your rabbit pages i have 2 years experience & i am a bunny addict yet you have made it simple for me to learn more thank you.

      yes i have fighter fish & this info is just what i have been looking for THANK YOU