Bacterial Infection

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What is a Bacterial Infection?

A bacterial infection can occur if there’s an overwhelming amount of bacteria in the betta’s aquarium or if the fish is in a high state of vulnerability (that is, if it has a very low immune system). It can also occur if there’s a foreign toxin or chemicals in the water.

How does a bacterial infection occur?

It’s not very clear to as how a betta contracts an internal bacterial infection. The main sign of a serious internal infection is dropsy and, it’s sad to say, once your betta contracts dropsy there’s no going back. If the fish’s internal organs have been weakened by chemicals or toxins in the water, they can become susceptible to bacterial infection. The organs will continue to be infected until they fail (either due to the bacteria or the toxins in the water, sometimes both).

All fish have what is called a ‘slime coat’. The slime coat (mucoprotein coating) is the fish’s main defense against infection and disease. It acts as a shield against disease-causing organisms in the fish’s external environment.

If there are toxins or chemicals in the water it can affect the slime coat, cause it to lapse and decay, which then makes the fish vulnerable to a bacterial infection. Even if an aquarium appears spotless, there’s still bacteria present in it, and if the fish is unwell, certain bacteria will start to infect the fish. This can then affect the fish’s scales and skin.


One of the noticeable signs of an internal bacterial infection is lethargy. Swim bladder disorder and dropsy can also occur. The betta may sit around a lot and flop to one side when perched on a leaf. It may also have difficulty swimming or may not eat as much. General reactions to the illness will also occur, such as a loss of colour and clamped fins.

You may notice a cloudy slime falling from the fish, or the betta may be covered in a slimy white layer if it is having problems with its slime coat. If the skin has a bacterial infection, white patches or blotchy sores can appear on the fish’s body.

Possible Cures

Different bacteria can affect the fish in different ways, but like any other bacterial infection, the best way to treat it is with an antibiotic. We find Ampicillin, Tetracycline and Kanamycin are the best antibiotics out there for fish, but there’s a whole range of antibiotics on the market, so have a good look around.

It’s good practice to isolate an infected fish before treatment if your betta isn’t the only inhabitant of its aquarium. Create what’s known as a quarantine or hospital aquarium so that the treatments or medicines don’t harm your other critters or plants. If any other fish also have the infection, be sure to put them in quarantine along with the betta (or even better, create a separate quarantine aquarium for each of them).

If the fish doesn’t need to be moved to a hospital aquarium, do a 80% water change. Be sure to pick out any debris, such as uneaten food and excrement, from the original aquarium water too.

The recommended dosage of medication will be specified on the medication bottle. Medicate the fish accordingly and do a 80% water change every 2 days. When running the medication, disconnect the filter, or run the filter but remove any carbon inserts as this will remove the medication from the water, rendering it useless. It’s also a good idea to add fungal medication to the treatment process too. This will prevent any oncoming fungal infections that your betta could contract due to the bacterial infection.

Recommended Medications

This list is by no means exhaustive, but here are some of the medications we recommend if you think that your betta does have a bacterial infection.

  • Tetracycline by API
  • Fungus Eliminator by Jungle
  • Ampicillin by Fish Chillin (This comes in capsule form, 1 capsule per 10 gallons, so if your aquarium is 2.5 gallons, for example, you’ll only want to add a quarter of the capsule per water change.)