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Home > Goldfish > Goldfish Turning Red? Here’s What to Do! (Vet-Reviewed)

Goldfish Turning Red? Here’s What to Do! (Vet-Reviewed)

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Dr. Luqman Javed

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Goldfish are beautiful ornamental fish that come in a variety of different colors, and it can be a cause for concern if you notice that your goldfish has developed a sudden and abnormal reddish coloration on their body. This redness can occur over different parts of their body such as the gills, tail, or patches.

Some goldfish can naturally have a red coloration or develop a reddish color as they start to mature. However, redness in goldfish is also associated with poor water quality that causes burns to develop on your goldfish.

There are several different reasons for a goldfish to start to turn red, whether it is a cause for concern such as an illness, or simply a natural color change. This article will give you all the answers as to why your goldfish might be turning red and what you can do to help.


Why Is Your Goldfish Turning Red?

1. Natural Coloration Changes

Goldfish changing colors when they are young is quite normal. Most varieties of goldfish may undergo color and pattern changes during the first few years of their growth. These color changes can also be influenced by the amount of sunlight they receive or the food that they are being fed.

Color in fish is controlled by chromatophores, which are pigmented cells that reflect visible light and produce the color that we see in fish. This makes a goldfish appear metallic, whereas the chromatophores responsible for red coloration are erythrophores. Goldfish who are exposed to more sunlight (such as in a pond) can develop a reddish coloration.

common goldfish inside the aquarium
Image Credit: JuanCarlosPalauDiaz, Shutterstock

2. Ammonia Poisoning

Ammonia poisoning occurs when the nitrogen cycle (establishment of beneficial bacteria) in an aquarium has not been grown properly or if this cycle has been broken in an aquarium. This can cause the ammonia levels to spike and burn your fish, causing red streaks and dots to appear on your goldfish. Red streaks on your goldfish are a good indication that something is not right with your aquarium’s water quality. Goldfish are quite sensitive to ammonia and can usually tolerate a level below 0.25ppm before they start to show signs of ammonia poisoning.

You may notice that your goldfish is covered in red streaks and gasping for air along the water surface which can later progress into black color, accompanied by a loss of appetite, clamped fins, and general lethargy.

3. Red Pest Disease

This is a common issue in ponds and aquariums with poor water conditions. The poor water quality can affect the slime coat of the goldfish allowing a bacterium (Bacterium cyprinid) to latch onto your goldfish. Weakened goldfish with poor immune systems are most at risk for developing this issue.

This is an easier disease to treat, and it can be prevented by ensuring that your goldfish aquarium and pond water is always kept clean. Red pest disease looks like red or pink patches on your goldfish’s body that typically starts at the base of your goldfish’s tail. Other signs include clamped fins and excess slime coat production.

Nymph goldfish in the water
Image Credit: Kateryna Mostova, Shutterstock

4. Septicemia

This issue will cause redness and swelling under the scales of a goldfish. Aside from the redness, goldfish will also show abnormal behavior and become lethargic. This can be caused by advanced stages of bacterial infections that infect your goldfish and these red skin lesions are typically difficult to treat in advanced stages.

Stress and pathogens are the most common causes, but open wounds exposed to poor water quality are another factor.

5. Ulcers

An ulcer is usually the result of a prolonged exposure to bacterial infection in very poor quality water, and often presents as a large red spot on the fish’s body. Though treatable in some cases, it requires quick intervention and drastic changes to fish husbandry and management.


How to Treat Goldfish a Goldfish That Is Turning Red

If your goldfish is turning red under natural circumstances, then there is nothing you can do to stop them from changing color naturally, unless you limit how much sunlight they receive or change their diet.

When it comes to treating a goldfish that has developed redness due to water quality issues such as high levels of ammonia, then you must do a large partial water change to dilute the ammonia. You can also give your goldfish salt dips in a separate treatment tank (following manufacturer doses) to help them heal from the injury faster.

Ensure that your goldfish aquarium is cycled before placing them inside, by letting the aquarium undergo the nitrogen cycle. You can also use filter media such as ammonia chips to help absorb excess ammonia in the aquarium when necessary.

Goldfish that are suffering from septicemia or red pest disease should be treated with the right type of medication to help kill off the pathogens. Water quality is also important in this situation, and you will need to ensure that you do frequent water changes and run a good filtration system to keep the water clean.

Strong medications in a treatment tank such as methylene blue or malachite green and other bacteria-killing fish medications should be administered to goldfish suffering from bacterial infections. However, their use is considered controversial from an environmental impact perspective. The dosage and treatment duration is usually shown on the packaging of the medication and should be followed closely.

goldfish in a fish tank
Image Credit: Tinh Nguyen, Unsplash



If you start to notice that your goldfish has begun turning red, you should first use a water testing kit to check if the ammonia levels have risen. If you find that there are no issues with the water quality in your goldfish’s aquarium, then it is best to look into the possibility of your goldfish being infected with a bacterial infection that needs prompt treatment for a successful recovery. It is best to seek veterinary care for a confirmation of a diagnosis.

Featured Image Credit: mrk3PHOTO, Shutterstock

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