Goldfish with red spots: causes and treatments (2023)

Goldfish have been selectively bred. Some features are isolated to produce the desired features. That's why goldfish come in a variety of color combinations, body shapes, scale types, and a variety of fin designs.

But what about the red spots? Are they the product of selective breeding? Why do they disappear and reappear after a while? Do the red dots indicate something else?

Goldfish with red spots: causes and treatments (1)

Join us for this article as we discuss what these unusual body colors are, what causes them, and how to treat them.

What are the red spots?

The red spots we see on goldfish are irritations. It can occur anywhere on the body (from head to tail).

It starts out as a pale spot that can only be seen with a magnifying glass. If left untreated, it turns into a massive purple or blood-red spot.

Don't settle and rest easy knowing that red spots are just irritations. These irritations have their roots in deadly origins, where the consequences can lead to mass mortality.

ammonia poisoning

Goldfish with red spots: causes and treatments (2)

Ammonia is an integral part of your aquarium water chemistry. It regularly diffuses into the water when fish release it through their gills as metabolic waste.

As fish excretion continues, ammonia levels also increase. When the ammonia level is high, the gills start to burn. This is the reason why ammonia poisoning is also calledammonia burn.

As an effect of burning ammonia in the gills, the fish will have difficulty breathing and excreting waste, since the common organ for both functions (which are the gills) is already damaged.

At this time, red spots begin to appear, but only on the gills, gill cover, eyes, and the rest of the head section. Note that the red spots caused by ammonia poisoning do not appear on the scales of goldfish.

What you should be concerned about is the internal effect of the ammonia. It damages the internal organs and the brain, and the possibility of death is high.

Don't expect only the red-spotted goldfish to die. Remember that all your fish in the tank share the same body of water. Since the ammonia level is already high, other residents will soon be affected and expect mass mortality, not only of goldfish, but other fish species as well.

Other symptoms of ammonia poisoning

In addition to the red spots on the head and gills, other symptoms may indicate ammonia poisoning, such as:

  • shallow breathing
  • shortness of breath
  • weakness and lethargy
  • loss of appetite

Treatment for ammonia poisoning

The ideal ammonia level for goldfish is between 0 and 0.25 ppm. You can measure ammonia levels usingcommercially available test kits.

You should perform a partial water change of up to 25% if the ammonia exceeds the optimal level. However, if it reaches 1 ppm or higher, stop what you are doing now and treat the situation as an emergency.

Carry out a water change of up to 50%. Make sure the temperature is the same for the old and new water. The temperature variation influences the ammonia peak.

Consequently, after a water change, you can use aammonia removal solution.

In the worst case, remove and quarantine your goldfish in another tank. Treat with antibiotics prescribed by your vet.

bacterial infection

The bacteria is the main cause of red spots in goldfish. In general, these bacteria come from the genera Pseudomonas, Flavobacterium, and Vibrio. However, certain types of bacteria cause specific diseases where red spots are one of the symptoms.

red plague disease

Goldfish with red spots: causes and treatments (3)

Causative bacteria:Aeromonas

Also called hemorrhagic septicemia, the red plague is an internal disease driven by Aeromonas. It is a cosmopolitan species that occurs naturally in all aquatic environments.

This rod-shaped bacterium enters a goldfish's body through seepage of water into the gills or ingestion of feces.

Once inside the body, the bacteria begin to multiply.

At an early stage, identification of Aeromonas bacterial infection is difficult. Your goldfish will not exhibit red spots and may present as a healthy fish.

The tiny red spots will only manifest in the midst of bacterial development. When they grow in number forming a colony, it is at this time that irritations similar to wounds appear on the skin.

If you see several large red spots, it's a clear indication that your goldfish's bacterial infection is at an advanced stage and mortality is likely to occur.

With an average survival rate of 20%, red blight disease is highly fatal to goldfish. Being highly contagious (not just to your goldfish, but to other resident fish as well) is one reason it leads to mass mortality.

Other symptoms of the red plague disease:

Additional symptoms can occur when your goldfish is suffering from the red plague disease. In addition to the red spots, symptoms include:

  • loss of natural body color
  • the snap of the eye
  • swollen belly
  • abnormal swimming behavior

red mouth enteric disease

Causative bacteria:Yersinia

As the name implies, the red spots occur mainly in the mouth of the goldfish. This disease is caused by the Yersinia bacterium.

Red plague (caused by Aeromonas) and enteric redmouth (caused by Yersinia) have much in common.

Both bacteria are precursors ofviral hemorrhagic sepsis. It enters the body of the goldfish through the gills and is highly contagious and deadly.

The unique factor with Yersinia is that they attack and multiply massively in the intestines, hence the word enteric.

Other symptoms of enteric red mouth disease:

Along with red spots in the mouth, symptoms of enteric red mouth disease include:

  • inflammation of the jaws and palate
  • bulging belly due to accumulation of fluid in the intestine

Treatment of bacterial infections

The treatment for red plagues and enteric red mouth is the same. But although they are similar, what we would like to highlight is identifying the degree of infection.

An early stage infection has a different treatment than those in advanced stages.

Outside toilet for early stage infection

An external bath is one option to treat superficial white patches, a symptom of an early-stage bacterial infection.

In a separate tank or container, place antibiotic infused water. Consult your vet about which antibiotics to use.

Nitrofurans and sulfonamides are common antibiotics to treat bacterial infections in goldfish. These drugs are broad-spectrum antibiotics that work on a variety of disease-causing bacteria.

Keep in mind that these antibiotics are only effective for early-stage infections, as they do not penetrate the skin and only treat superficial infections.

Mix, apply antibiotics, and dip fish according to specifications and prescription.

In addition to your infected goldfish, consider diving with other resident fish, as the bacterial infection that causes the red spots is highly contagious.

In some cases, the red spots may reappear. To prevent recurrence, soak fish for one hour a day for three days or until symptoms subside.

In case of adverse effects (such as redness of the spots), remove the fish immediately, stop the treatment and send it to the vet.

Medicated feeds for advanced bacterial infection

Large, bloody red spots are a clear indication that your goldfish is suffering from a late-stage bacterial infection.

Treatment of advanced bacterial infection requires a combination of external baths and diet medication. The focus here is that the baths are for external treatment while the medicated rations are for internal treatment.

Unlike humans, goldfish cannot take medication. Your medications should be mixed with your diet.

The good news is that you can make your own medicated food. But again, what is crucial is the type of antibiotic to mix when preparing the food. Consult your vet for a prescription for antibiotics. Make sure it's in powdered form to make mixing easier.

Ingredients for Medicinal Piensos

  • Prescription antibiotic (in powder form)
  • dry gelatin
  • Fish food (pellets or scales)

Procedure for the preparation of medicated rations

  • Add 30 grams of ground fish food, 100 grams of powdered gelatin and 1 tablespoon of powdered antibiotic to a bowl
  • homogenize
  • Boil 2 cups of water
  • In small amounts, slowly add the powder mixture.
  • Stir constantly until a gel forms.
  • Pour the gel into a mold. Let it cool in the freezer until it hardens.
  • Cut into small squares (about the size of the fish's mouth)

Medicated food application

  • Starve your goldfish
  • In small amounts, place medicated feed in the tank.
  • Let each feeding last 5 minutes.
  • Collect uneaten medicated food
  • Feed twice a day for 10 days.
  • The shelf life of medicated feed is only 10 days.

Stressors and How to Prevent Red Spots on Goldfish

Bacterial infection and ammonia poisoning are exacerbated if stressors are evident in your tank. Without these conditions, the degree of irritation may be minimal and the survival rate of your goldfish will likely increase.

Surprisingly, preventing red spots on goldfish is easy, as the technique behind its prevention is part of tank maintenance. This means that you do not need special preparations.

water condition

A fish's immune system is its main defense against disease. But with poor quality water, expect your defense mechanism to give up and disease to start to invade.

With frequent water changes and a good filter, the water quality stabilizes. Clean the filter from time to time. Soon, it may be the source of contaminants.

stock density

In addition to being overcrowded with limited swimming space, too many fish can significantly deteriorate water quality.

Remember that all fish naturally excrete ammonia as metabolic waste. More fish means more ammonia.

Stay within the recommended breeding density. Usually aquarists follow the one inch rule. That means you can put in a 1 inch fish for every gallon of water.

fish nutrition

Food quality can influence the health of a fish's immune system. Cheap, low-quality feed lacks the necessary vitamins and minerals.

Invest in high-quality food formulated for goldfish. Although expensive, it will be cheaper in the long run when compared to the expenses incurred in treating an infected goldfish.

While not part of tank maintenance, the age of your goldfish can become a stressor for disease. The older the goldfish, the more prone to disease. While it's a given factor, it doesn't mean you can't take care of your old goldfish.

Provide your goldfish with the best care and environment, and the chances of contracting red spots and other diseases are unlikely.


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frequent questions

Are red spots on goldfish normal?

No. They indicate a bacterial infection or ammonia poisoning. Some aquarists treat red spots as an emergency. Death is imminent if not treated on time and properly.

Are bacteria and ammonia found naturally in the tank?

Yes. Bacteria are cosmopolitan species and can be found in all bodies of water. On the other hand, ammonia is infused into the water as a byproduct of the metabolism of the fish.

Are the red spots on goldfish contagious to humans?

No. Unlike the zoonotic features of foot-and-mouth disease in cattle and avian influenza in birds, the red spots on goldfish are not contagious to humans. There were no reports of infections.


Red spots on goldfish can be avoided by following proper tank maintenance and hygiene. And it doesn't mean you're unhealthy if your goldfish is infected. Remember that bacteria and ammonia occur naturally in the tank.

In the end, what we most recommend is that you look at your aquarium and its resident fish daily. This way, you're having fun while watching out for the first signs of red spots. And spotting the early symptoms would mean early treatment and survival for your beloved goldfish.

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