What are the Uses of Amoxicillin for Fish?

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  • Written By: Marlene Garcia
  • Edited By: Jenn Walker
  • Last Modified Date: 22 September 2019
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Amoxicillin is an antibiotic related to penicillin that stops bacteria from multiplying. The use of amoxicillin for fish can treat several bacterial infections caused by water in fish tanks that is too warm or poorly maintained. When a fish is sick or injured, it allows the bacteria to flourish, which may kill the fish if not treated quickly. The aquarium owner can use amoxicillin for fish that show symptoms of fin rot, red pest, tuberculosis, scale deformities and dropsy.

Fin rot is a common disease seen in gold fish and neon tetras. It begins with whitish sores on the fins that may turn orange or yellow in a few days and spread to the gills. Affected fish might develop mucus that impedes respiration and can cause death. These fish might stay at the top of the tank or at the bottom as they try to breathe; they also may stop eating if the bacteria spreads to the mouth. Using amoxicillin for fish with this condition can sometimes retard the spread of the bacteria.

The most common sign of red pest on ornamental fish are bloody streaks on the fins, body or tail. The condition can become so severe that the tail or fins actually fall off if not treated with amoxicillin. This is an internal bacterial infection that can be addressed by adding the antibiotic to the fish’s diet. It is rarely seen in healthy aquariums.


Amoxicillin for fish with tuberculosis is not always effective because this disease is hard to cure. It is not the actual tuberculosis that affects humans but is a closely related bacterium that attacks certain fish. This slow-growing condition may cause sores and lead to the loss of scales or a curving of the spine. Infection might spread to humans, especially if a cut or scrape on the hand comes into contact with bacteria in the tank.

Dropsy and scale protrusion can be identified by scales that stick out on the fish’s body. Dropsy might also cause the body to swell, and red sores or streaks might appear. Scale protrusion usually first appears in patches when pustules under the skin affect respiration. As the disease progresses, the fish may lose scales and eventually die. Using amoxicillin for fish with these conditions could be effective if used early.

Amoxicillin capsules can be added to a fish tank for five to 10 days. The infected fish should be isolated in a separate tank during treatment so other fish are not exposed to the bacteria. Tanks also should be sterilized after using amoxicillin for fish that show signs of bacterial disease.


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Post 3

One of my goldfish is showing signs of a bacterial infection. The other two aren't, but if the bacteria is in the water, I think they might develop it too. I'm thinking of keeping them together and adding the amoxicillin into the tank today. This is a good idea right?

If I separate them and treat only the one, I'm afraid that the other two will re-introduce the bacteria to the tank when they come back. So I might as well treat them all and then clean the tank and renew the water.

Has anyone here used amoxicillin for fish before? Is this what you did?

Post 2

@fify-- Amoxicillin for fish is a separate product and you can get it from the vet's office or from feed stores.

I have never used amoxicillin made for human use as fish antibiotics. But I have heard from a friend that the amoxicillin sold for fish is the same thing as the one that's prescribed for people. I suppose if you don't have access to fish amoxicillin, you could use the prescription version as long as you ask the vet about the dose. If you overdose the fish, it could be fatal, so be careful about that.

Post 1

Can I use amoxicillin made for humans, for fish?

Or do I need to buy amoxicillin that's specifically formulated for fish? Where do I get this, from the vet?

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