Why Is My Goldfish Turning Black: We Check 6 Possible Claims

why is my goldfish turning black
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The most common colors of goldfish in pet stores are red, orange, shiny-orange, yellow, brown, a mix of orange and white, or white and red.

What color is yours?

If you bought your goldfish with these radiant colors, you might be surprised if their body color changed. Some goldfish owners observe their goldfish turning black as they age.

If the question on your mind is, ‘Why is my goldfish turning black?’, this article will provide answers and whether you should be concerned.

Reasons Why Your Goldfish Is Turning Black

The following are reasons why your goldfish’s body is turning black.

1. It Is Genetic

two goldfish in fish tank

Some goldfish species have black coloration in their genes that develop within the first and second years. Since genetic predisposition is completely natural, there is no need to worry about your goldfish’s health if their color changes.

Mixed breed goldfish from untrustworthy breeders are more likely to turn black as they transition from juveniles to adults. The extensive cross-breeding will cause these cheaper goldfish to have strange colorations that may slowly develop into dark patches.

That is not to say that purebred goldfish do not develop black spots. On the contrary, goldfish from reputable breeders can experience color change, but it often starts as small, black dots or streaks on the fins. With time, these black patches get larger.

There is nothing to worry about if your goldfish turn black due to genetics. Your fish will be generally healthy. However, if your goldfish’s natural color does not contain dark pigment variation, then there is another cause for the color change.

2. It’s Camouflage

Did you know goldfish can change their body color to blend with their environment?

goldfish with discoloration on body

If you keep goldfish in a dark environment, their pigment cells will produce melanin to camouflage.

Melanin is a dark pigment that gives a fish darker color. The pigment may cover the scales, fins, tail, or entire body.

If your goldfish tank does not receive light exposure, the fish will produce more melanin and appear darker. This natural trait is particularly helpful in the wild as it protects goldfish from prey. Goldfish can also lose their natural colors and turn white if their aquarium is not exposed to light.

Fortunately, you can remedy this by moving the fish tank to a spot where there is natural light. Alternatively, brighten the dark background with aquarium lights to restore the fish’s vibrant colors and reduce the likelihood of having black goldfish.

3. Ammonia Burns

Ammonia poisoning could also be the cause of your goldfish turning black. Ammonia is a toxic chemical not just for goldfish but other fish. Even 2 ppm of ammonia can potentially kill your goldfish.

various goldfish in aquarium

The fish tank can have ammonia buildup from fish waste, rotting food, dead plants, dead fish, inadequate filtration, or keeping too many fish.

Ammonia burns the goldfish’s skin and gills. Unfortunately, ammonia burns are not evident to the human eye. It is not until the fish’s body starts healing that goldfish develop black spots.

But do not assume that goldfish turning black is a sign that the ammonia levels have dropped. This fish species will attempt to heal the ammonia burns even when the levels are elevated. Other signs of ammonia burn are labored breathing, erratic swimming patterns, and reddened gills.

Use an ammonia test kit to confirm that your goldfish is turning black from ammonia poisoning. Also, test for nitrites as they, too, are dangerous.

Once you confirm the black spots are due to ammonia burn, perform a 50% water change. Additionally, conduct a weekly 25% water change to reduce ammonia levels. Alternatively, use ammonia removal products.

You can prevent ammonia spikes if you:

Install A Powerful Filtration System

A filter willmaintain water quality and become home to the beneficial bacteria in the aquarium. Opt for filters that provide mechanical, chemical, and biological filtration.

Change Water Regularly

Regular tank maintenance is also important since these fish are messy. Ensure you vacuum the substrate and wipe the aquarium glass on the inside.

Add Live Plants

Plants absorb ammonia levels directly with their roots. They use this compound to grow, which helps maintain water quality.

Avoid Overfeeding

Since leftover food can cause ammonia to burn, avoid overfeeding and remove uneaten food. Provide enough food that your goldfish will eat in a few minutes, not the whole day.

Avoid Overstocking

Goldfish produce a high bioload, which means an overstocked tank is a quick recipe for ammonia poisoning. When housing goldfish, provide 1 gallon of water for every inch of fish. Add a few extra gallons to promote the fish’s active nature and make room for tank decorations.

Avoid Goldfish Bowls

goldfish in fish bowl

Avoid keeping your goldfish in bowls as they are more prone to chemical burns and developing black scales. Goldfish bowls lack a filtration system and beneficial bacteria.

Cycle Your Tank

Completing the nitrogen cycle ensures the tank has populations of beneficial bacteria to break down ammonia levels. Cycling provides a healthy environment for aquatic life.

How long does it take for the black spots to clear? Well, it could take a few hours, days, weeks, or never. Some goldfish recover within a day, while others carry the dark spots throughout their life. We recommend using products that help repair your fish’s damaged slime coat during this time.

Factoid: Simulating the natural water cycle to keep fish healthy and well-maintained is one of many challenges any aquarium enthusiast should learn to learn! One way of doing this is by introducing a machine that will allow you to circulate aquarium water effectively. Read our post about this accessory you probably would need sooner or later — Do Goldfish Need A Bubbler: Practical Aesthetic Or No Need.

4. Black Spot Disease

Though rare, black spot disease can also be the reason behind goldfish developing black spots. This disease is more prevalent in wild goldfish and those in outdoor ponds than those in indoor tanks.

goldfish with 2 snails in a tank

Black spot disease is spread by infected water snails with parasitic fluke disease.

It can also be a result of bird droppings that get into the pond water.

The parasite enters the goldfish’s body as larvae and lays eggs that develop into black cysts. It is these eggs that you will identify as black patches. With time, the cysts grow and burst to release more parasites.

If your goldfish has black spot disease, they will constantly rub their bodies against surfaces in the tank to get relief from their itching bodies.

But, you can treat black spot disease by removing snails from the tank water. Doing so shortens the parasite’s life cycle and allows your fish to heal.

Although this disease can be a worrying sight, it is not as life-threatening as ammonia burn.

Here is a YouTube video outlining common goldfish diseases:

5. Stress

Stress could also be why your goldfish is turning black. A goldfish can get stressed from living with an aggressive tank mate, poor water conditions, strong water flow, a new environment, or long shipping hours.

Goldfish turn black on their scales and fins, but this can be remedied by eliminating the negative stimuli. Once your fish are less stressed, they will regain their beautiful colors.

Your goldfish’s scales can also turn black from a bacterial infection. Stressed fish are more prone to bacterial infections since stress weakens the immune system. Nevertheless, you can use antibacterial medication to treat bacterial infections.

6. Injuries

Goldfish turn black as they heal from their injuries. Unlike humans who develop scar tissue or scabs, goldfish have black spots as proof they are recovering.

You can take preventative measures to prevent future injuries by removing any sharp objects or aggressive bullies.

How To Prevent Your Goldfish From Developing Black Patches

You can prevent the likelihood of your goldfish turning black by:

Maintaining Water Quality

goldfish in aquarium image

Aim to keep the tank water clean and free of ammonia by conducting partial water changes and removing plant debris, uneaten food, and fish poop. An ammonia test kit will help you monitor the ammonia level.

Providing Adequate Lighting

A dark environment will trigger your goldfish to produce melanin to camouflage. But, a well-lit aquarium will prevent your fish from turning black.

Avoiding Aggressive Tank Mates

goldfish with other fish in tank

Only keep your goldfish with compatible tank mates to prevent bullying and stress.

Maintaining Water Parameters

Ensure the water temperature, pH, and hardness remain at the optimal range for a goldfish. Additionally, ensure you treat the tap water before adding it to the fish tank.

Quarantining New Fish

Before you add new goldfish, observe them in a quarantine tank for at least two weeks. Doing this will prevent the introduction of parasites and diseases.

Removing Snails

Snails can harbor internal parasites and spread them to your goldfish. This is why you should remove them from the aquarium.

Remember, you cannot prevent a genetically predisposed goldfish from developing black marks. For instance, the Black Moor and Shubunkin are destined to develop black patches.

Related Questions

Can Goldfish Gain Their Vibrant Color After It Turns Black?

Some goldfish regain their natural color while others don’t. It depends on why the goldfish turned black in the first place.

When a goldfish turns black due to genetic predisposition, its color change will last its lifetime.

The positive thing about this is it does not affect the fish’s health.

If the change was due to injuries, chances are your goldfish will regain their color after they make a full recovery. In the event of severe ammonia poisoning, the black patches may or may not fade away.

You can offer color-enhancing goldfish food from reputable brands to boost your pet’s body color. Or, feed carrots and garden peas as they are rich in carotenoids that naturally enhance the color of these beautiful fish.

Why Is My Goldfish Turning White?

If your goldfish starts to turn white, it could be due to poor water quality, an illness, or exposure to little or excess sunlight. A parasite infestation, old age, poor diet, and low oxygen levels can cause goldfish to turn white.

Final Thoughts

Sometimes, your goldfish turning black should not be a cause to worry about. It is normal for goldfish to develop black patches from living in a dark aquarium or their genetics have black color variation.

However, if your goldfish is developing black spots from ammonia poisoning, Black spot disease, stress, or injuries, you must take the necessary steps to keep your fish healthy.

Keep the goldfish tank clean, maintain water quality, and reduce stressful stimuli.

Last Updated: July 28, 2022

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