Goldfish with Red Spots: Causes and Treatments

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Goldfish have been the subject of selective breeding. Some characteristics are isolated to produce desired traits. It is why goldfish have several color combinations, body shapes, scale types, and an assortment of fin designs.

But how about red spots? Are they a product of selective breeding? Why do they disappear and reappear after some time? Do red spots indicate something else?

goldfish with red spots
Source: @simon05.kc

Join us in this article as we examine what these unusual body colorations are, what causes them, and how to treat them.

What Are Red Spots?

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

It starts as a tiny dot with pale coloration that can only be visible with a magnifying glass. If untreated, it progresses into a massive patch with a purple or blood-red color.

Don’t settle down and be calm after knowing the red spots are simple irritations. Those irritations are rooted in deadly origins where the consequences could often lead to mass mortality.

Ammonia Poisoning

Goldfish Ammonia Poisoning
Source: @riauaquanature

Ammonia is an integral part of your aquarium’s water chemistry. It is regularly diffused in the water as fish release them through their gills as metabolic waste.

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

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

At this moment, red spots start manifesting, but only in the gills, gill cover, eyes, and the rest of the head section. Be aware that red spots caused by ammonia poisoning do not occur in the goldfish scales.

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

Don’t expect that only the goldfish with red spots will die. Remember that all your fish in the tank share the same body of water. Given that the ammonia level is already high, other residents will soon be affected and expect mass mortality, not just for goldfish but other species of fish as well.

Other Symptoms of Ammonia Poisoning

Aside from red spots in the head and gills, other symptoms can indicate ammonia poisoning, as follows:

  • surface breathing
  • gasping for air
  • Weakness and lethargy
  • Loss of appetite

Treatment for Ammonia Poisoning

The ideal ammonia level for goldfish ranges from 0 to 0.25 ppm. You can measure ammonia levels using commercially available test kits.

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

Perform a water change of up to 50%. Make sure that the temperature is the same for the old and new water. Temperature variation influences ammonia to spike.

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

In a worst-case scenario, remove and quarantine your goldfish in another tank. Treat with antibiotics as prescribed by your veterinarian.

Bacterial Infection

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

Red Pest Disease

Goldfish Red Pest Disease
Source: @g_o_g_o_99

Causative bacteria: Aeromonas

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

This rod-shaped bacteria enters the body of a goldfish either through water filtration in the gills or feces ingestion.

Once inside the body, the bacteria start to multiply.

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

The tiny red spots will only manifest halfway through bacterial development. When they grow in numbers forming a colony, this is the time that the wound-like irritations on the skin will show up.

If you see several large red spots, it is a clear indication that the bacterial infection of your goldfish is in the advanced stage and that mortality is likely to occur.

Averaging at a 20% survival rate, red pest disease is highly fatal to goldfish. Being highly contagious (not just to your goldfish but to other fish residents as well) is one of the reasons why it leads to mass mortality.

Other Symptoms of Red Pest Disease:

Additional symptoms may exhibit when your goldfish is suffering the red pest disease. On top of red spots, symptoms include:

  • loss of natural body coloration
  • the popping of the eyes
  • bloated belly
  • Abnormal swimming behavior

Enteric Redmouth Disease

Causative bacteria: Yersinia

As the name suggests, red spots occur mainly in the goldfish’s mouth. This disease is brought out by the bacteria Yersinia.

Red pest disease (caused by Aeromonas) and enteric redmouth disease (caused by Yersinia) have a lot in common.

Both bacteria are precursors of viral hemorrhagic septicemia. It enters the goldfish body via the gills, and they are highly contagious and deadly.

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

Other symptoms of the enteric redmouth disease:

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

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

Treatment of Bacterial Infection

The treatment for red pests and enteric redmouth disease is the same. But while they are similar, what we would like to emphasize is to identify the degree of infection.

An early-stage infection has a different treatment than those that are in the advanced stages.

External Bath for Early-Stage Infection

An external bath is an option for treating superficial white spots – a symptom of early-stage bacterial infection.

In a separate tank or container, place water infused with antibiotics. Consult your veterinarian on what 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 range of disease-causing bacteria.

Take note these antibiotics are effective only for early-stage infections as they do not penetrate the skin and only treat superficial infections.

Mix, apply the antibiotics, and dip the fish according to specification and prescription.

Aside from your infected goldfish, consider dipping other fish residents as the bacterial infection causing red spots are highly contagious.

In some cases, the red spots may recur. To prevent recurring, dip the fish for an hour daily for three days or until the symptoms are gone.

In case of adverse effects (like reddening of the spots), remove the fish immediately, stop the treatment and refer back to your veterinarian.

Medicated Feeds for Advanced Bacterial Infection

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

Treating advanced bacterial infection requires a combination of external baths and feed medication. The approach here is that the baths serve as external treatment while the medicated feeds are for internal treatment.

Unlike humans, goldfish cannot take medicines. Their medicines have to be mixed in their feed.

The good news is you can make your own medicated feed. But again, what is crucial is the type of antibiotic to be mixed in making the feeds. Consult your veterinarian for an antibiotic prescription. Make sure it is in powder form for easy mixing.

Ingredients for Medicated Feeds

  • Prescribed antibiotic (in powder form)
  • Dry gelatin
  • Fish food (pellets or flakes)

Procedure for Making Medicated Feeds

  • Add 30 grams of grounded fish food, 100 grams of gelatin powder, and 1 tablespoon of antibiotic powder in a bowl
  • Mix thoroughly
  • Boil 2 cups of water
  • In small amounts, slowly add the powder mixture.
  • Stir constantly until it forms a gel.
  • Pour the gel into a mold. Allow to cool down in a freezer until hardened.
  • Cut into small squares (approximately the size of your goldfish mouth)

Application of Medicated Feeds

  • Starve your goldfish
  • In small amounts, drop medicated feeds in the tank
  • Allow each feeding to last for 5 minutes
  • Collect unconsumed medicated feeds
  • Feed twice a day for 10 days
  • The shelf life of medicated feeds is good for 10 days only.

Stressors and How to Prevent Red Spots in Goldfish

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

Surprisingly, preventing red spots in goldfish is easy as the technique behind its prevention is part of tank maintenance. This means that you don’t need special preparations.

Water Condition

The immune system of a fish is its primary defense against illnesses. But with poor water quality, expect that their defense mechanism will surrender and disease will start invading.

With frequent water changes plus a good filter, water quality becomes stable. Clean your filter once in a while. It may soon be the source of contaminants.

Stocking Density

Aside from becoming overcrowded with limited swimming space, too many fish can significantly deteriorate water quality.

Remember that each fish naturally excretes ammonia as metabolic waste. More fish means more ammonia.

Stay within the recommended stocking density. Usually, aquarists follow the one-inch rule. It means you can place a 1-inch-sized fish for every gallon of water.

Fish Nutrition

The quality of food can influence the health of a fish’s immune system. Cheap and low-quality feeds lack the needed vitamins and minerals.

Invest in high-quality feeds formulated for goldfish. While it is expensive, it will become cheaper in the long run if you compare it with the expenses incurred in treating an infected goldfish.

While it is not part of tank maintenance, the age of your goldfish can become a stressor for diseases. The older your goldfish, the more prone to illnesses. While it is a given factor, it does not mean that you don’t take care of your old goldfish.

Give your goldfish the best care and environment, and the chances of getting red spots and other diseases will be unlikely to occur.



Are Red Spots in Goldfish Normal?

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

Are Bacteria and Ammonia Naturally Occurring in The Tank?

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

Are Red Spots in Goldfish Contagious to Humans?

No. Unlike the zoonotic features of foot and mouth disease in livestock and avian influenza in birds, the red spots in goldfish are not contagious to humans. No reports of infections have been recorded.


Red spots in goldfish can be prevented if you follow proper tank maintenance and hygiene. And it does not mean you’re being unsanitary if your goldfish is infected. Remember that bacteria and ammonia are naturally occurring in the tank.

At the end of the day, what we highly advise is to look at your aquarium and its fish residents every day. In this way, you are enjoying while monitoring for early signs of red spots. And detecting early symptoms would mean early treatment and survival of your beloved goldfish.

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