Goldfish Red Pest Disease Treatment {Symptoms, Causes & Treatment}

The red pest disease is one of the common illnesses that affect goldfish. It is a disease that causes bloody streaks to appear on the fins, tail, and body of fish.

This condition can cause a significant deterioration in the overall living quality of goldfish, hence, a need for rapid treatment action.

In this article I will show you how to identify red pest disease in your goldfish and what you should do to treat it.

Goldfish Red Pest Disease Treatment

Checklist Of Things You Will Need

Below is a list of things you will need for this guide

  1. Water Testing Kit (Available on Amazon)
  2. Aquarium Salt (Available on Amazon)
  3. Methylene Blue (Available on Amazon)

Treatment Of Red Spot Disease In Goldfish

To treat red spot disease in goldfish you should move the infected goldfish in to a seperate tank then add aquarium salt to the water as well as a bacterial medications such as Methylene Blue.

Red spot disease will be caused by a bacterial infection and the best way to cure this is to add aquarium salt and Methylene Blue to the aquariums water.

You should also improve the quality of the water and the overall cleanliness of the tank. You can carry out some water testing to know the exact area where you need to improve the water parameters. You might not necessarily have to isolate the affected fish because the disease is not contagious.

Adding antibiotics to the food of goldfish is the ideal quantity, but you might have to increase it a little bit in severe cases. It is not advisable to use a more potent dose if the situation is not critical to avoid unwanted side effects. Goldfish might not want to eat medicated food ordinarily; therefore, the best thing to do is to starve them a little bit before feeding them.

The water condition of the tank is also a significant factor that can determine how the disease will thrive in the tank. Bacterial infections are not common in clean aquarium tanks; you can, therefore, prevent these diseases by ensuring that your aquarium tank is kept clean at all times.

What Is Red Pest Disease?

Red pest disease is a disease that significantly affects the general welfare of fish. The condition causes red spots on fins and tails of fish, thus allowing it to appear like the fish is bleeding. These bloody streaks can appear on fish fins, tail, and body of the fish.

The bloody streak does not have to appear in all the parts before you know it is red pest disease. It sometimes affects only either the body or fins. The causative bacteria agent of this disease is an opportunistic bacterium and often gets a hold on weakened fish.

These streaks could proceed to become ulceration, and it can consequently lead to fin and tail rot. In severe cases, the decay can cause tails and fins to fall off entirely.

Red pest disease mostly affects weakened fish or fishes that are living under a poor water condition. It is sporadic for red spot disease to affect healthy fish living under healthy conditions in a clean tank. It is not a contagious disease, and other fishes cannot be infected.

What Are The Red Spots On My Goldfish?

The red spots on a goldfish are a sign that there are external parasites on your fish.  The red spots are rashes that have developed from the irritation.

If the red spots are large enough to see with the eye then the condition is quite serious.

If your goldfish is turning black take a look at this article to find out why.

How Do You Treat Red Spots In Goldfish

To treat red spots in goldfish you will need to do the following

  • Test the aquariums water using a Water Testing Kit
  • Replace 50% of the water in your aquarium
  • Add aquarium salt to the water
  • Add Methylene Blue to the water

Causes Of Goldfish Red Pest Disease 

Red spot disease in goldfish is mostly as a result of bacterial infection and poor water quality. In most cases, these two factors can complement each other to make goldfish susceptible. Ordinarily, these causative bacteria cannot get hold of healthy fishes, and poor water quality can affect the health of the fish.

Red pest disease can be a result of infection from a bacterium known as Bacterium cyprinid, which is an opportunistic organism that cannot affect healthy fishes.  Bacterium cyprinid is a pathogenic bacterium common in aquariums, ponds, and other aquatic environments.

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Likewise, red spot disease can also be caused by a fungus known as Aphanomyces invadans. It is typical for showing red lesions or bleeding streaks; it can result in deep ulcers. Aside from the fact that this fungus can cause red spot disease on its own, it can also make room for secondary bacterial infection.

Also, non-living factors can be responsible for the red spot disease in fish. Poor water conditions, poor feeding, high level of ammonia, high nitrate level, and other water parameters can significantly affect red spot disease in goldfish.

Ammonia poisoning is one of the most significant factors that can make goldfish susceptible to red spot disease. Ammonia poisoning happens when the nitrogen cycle of the tank is offset by the increase in the tank’s pH. The deterioration caused by ammonia is evident because of the red streaks or bloody patches on their body and fins.

Severe ammonia poisoning can also lead to damage to the brain, central nervous system, and other internal organs of the fish.

Is Red Pest Disease Contagious In Goldfish

Red pest disease itself will not spread from one goldfish to another, The disease is spread through poor water conditions, so if one of your fish has the disease, your other goldfish will most likely also get the disease.

Red pest disease will attack and infect goldfish that have weak immune systems.  If your fish are in poor water conditions it is only a matter of time before they will get poorly.

The red pest disease will come from some bad bacteria in your tank, check for the source such as

  • Dead Fish
  • Rotten Food
  • Blocked / Dirty Filter
  • High or Low Levels of pH and Ammonia

Recommended Antibiotics For Treatment

There are a variety of antibiotics that can be active as internal medication for red spot disease. Tetracycline and chloromycetin [chloramphenicol] are the two most common antibiotics that are effective in the treatment of red spot disease. The concentration of these antibiotics is also crucial in determining how effective it will work.

If for some reason, the fish fails to ingest the food, you can add the antibiotics directly into the tank. You can add 10mg of antibiotics per 1 liter of water. This method is, however, not as effective as mixing antibiotics with fish food.

You can also clean the tank with fish disinfectants like acriflavine [trypaflavine] and monacolin [mono aminoacridine] to water if you perceive the presence of the red pest in the tank. You should, however, discontinue the use of antibiotics if the fish are not comfortable with it.


Red spot disease in goldfish can be a significant cause of concern to aquarium owners. It is life-threatening and can result in the overall deterioration of fish life. Nevertheless, this disease can remain under check by ensuring that your fish live under perfect conditions. You can also get rid of this disease with the simple use of antibiotics.



Hello, I'm Jason. I'm the guy behind I volunteer at my local fish shop and I created this site to offer tips and advice on the fish I care for.

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