Why Is My Goldfish Turning Black? [What It Means and How You Can Cure It]

A goldfish turning black is not a pleasant sight to see, especially with its bright gold color replaced by black spots. A black goldfish will arouse a lot of concern from you as a pet owner. Seeing your beautiful aquarium pet with its shiny scales suddenly taking a strange appearance with its skin covered in black spots is not normal.

This may cause your thoughts to center around worry or concern for your goldfish’s health and the fear of losing it, which is typical for a lover of these little aquarium pets.

Although there are several reasons to explain why your goldfish can turn black, it is still most advisable to investigate before blowing things out of proportion. Most of the time, the reason for the color change is not always detrimental to the health of your goldfish.

We’ll discuss some of the reasons your goldfish can experience a change in color, their causes, how you can handle it, and some preventive measures to avoid this.

Why Do Goldfish Turn Black?

Are you wondering why is my goldfish turning black? It might be pretty difficult to believe or accept, but some of the causes or reasons for a goldfish turning black can be natural and in no wise signify health problems or harmful to your fish’s health.

Some of the causes of a goldfish turning black might be chemical reactions, presence of ammonia in your tank, genetic makeup, environment, stress, or illness. Here are some of the reasons why goldfish turns black.

Adapting to its Environment

One of the natural reasons behind the black spots on your goldfish’s skin can be melanin production. All fish have different cells, and some of these cells can produce a black pigment called melanin which could cause a change of scale color on your fish.

Your goldfish could also produce lots of melanin due to trying to adapt to the color of its environment. This can most likely happen if its aquarium is covered in black spots and the inherent protective instinct of a fish is to adapt to color change to be protected from predators.

These color patches can spread throughout the scale to the fins and the whole body of the fish. This type of color change is naturally caused and has no adverse or health effects on the fish. It is nothing to worry about.

Genetic Makeup

Another reason to explain the color changes on the scale of your goldfish could be its genetics. Many species of goldfish are blended (mixed) breeds. This means they have not been carefully bred to maintain specific qualities, such as coloration.

Suppose your goldfish happens to be one of these breeds. In that case, it may experience changes in its color at its first year of life or gradual color transitions as it matures, with lighter areas appearing alongside darker areas as it develops.

This cause of color change is not harmful to the fish but a reaction to its genetic makeup.

Ammonia Poisoning

One of the most dangerous causes of color change in a goldfish can be ammonia poisoning. If you notice your goldfish’s scales or fins turning black, it could be that your fish is suffering from ammonia poisoning.

Goldfish are a notoriously messy creature that produces a lot of waste when regularly overfed. Still, when their waste isn’t cleaned up, and leftover food is left in the aquarium, the waste rots and releases toxic ammonia into the water.

This ammonia is incredibly toxic to the fish and can cause burns on the fish’s skin, leading to severe health issues and ultimately to your fish’s death. To prevent this, make sure to check your water parameters often.

Ammonia is produced chiefly in new tanks and bowls because new tanks’ filtration systems don’t work to remove waste or produce clean water in the fish tank for up to a month. High ammonia levels in the water can cause caustic burns that will injure the skin, fins, tail, gill plates, body, and head of the fish.

Ammonia poisoning can cause a lot of pain and discomfort for your fish. When you notice your fish starts getting irritations, make sure you remove the waste and give your water a 60% change. This will cause the ammonia levels to begin to drop, and damaged skin and fins will heal.

The appearance of black patches will replace the burn areas, and these patches will probably remain forever due to the severe damage caused to the body of the fish due to ammonia poisoning.

With that said, it’s impossible to see ammonia in water without a proper aquarium test kit.

Black Spot Disease

Many goldfish pet owners express concern and fear at the sight of a color change in their fish. They mainly conclude it to be a result of their fish contracting the black spot disease, which is, most times, not the cause of the problem as the black spot disease is pretty rare, especially in adult fish.

Black spot disease can only be considered the cause of your fish turning black if you keep snails in the same tank with them, and more likely to happen in an outdoor pond than in an aquarium.

A parasite, not an infection, primarily causes black spots. These parasites lay eggs that turn into larvae, then burrow into the skin of the fish. As a result of this, the fish will start to form hard cysts to protect themselves. These cysts are very dark or black, which is where the name comes from.

It will likely start flicking its tail and rubbing against surfaces because of the irritation. At the slightest observation of these cysts and black spots on your goldfish, remove the snails from the tank immediately.


Another reason for your goldfish turning black can be overfeeding. Goldfish are particularly prone to this problem, especially after a change in environment but overfeeding a goldfish could be very dangerous to their health.

Not only does it lead to the production of more waste in the aquarium, but it can prevent your goldfish filter from working. This, in turn, can lead to other problems that can result in your fish turning black, becoming ill, and potentially dying of swim bladder disorder or ammonia poisoning.


If stress is the cause of the change in your goldfish color, give it a little time to help it recover. If the color change persists, you’ll need to consult your veterinarian to get some help.

Will Your Goldfish Be Black Permanently?

The answer to this is solely based on the situations that led to its change in color. A goldfish will return to the regular coloring if the causes are genetic, and some other times, your fish won’t.

If your fish is changing color due to the environment, make sure to remove dark elements such as a background or dark aquarium, and he will likely return to that same vibrant orange.

However, genetics, most illnesses, and ammonia poisoning will result in permanent color changes.

How To Prevent Goldfish From Turning Black In The Future?

A color change is one of the most frightening situations for a goldfish owner to handle. However, bear in mind that goldfish are fragile creatures that deserve all the protection they can get to live their best lives. Ensure you give topmost attention to your goldfish, its cleanliness, health, and protection.

Having answered the question, “why is my goldfish turning black?” we’d look at some ways to prevent it from happening again in the future for other goldfish.

  1. Regularly check for ammonia levels in your goldfish aquarium tank with an ammonia test kit.
  2. Avoid overfeeding your goldfish. Always ensures to remove leftover food.
  3. Regularly check for waste and ensure the aquarium is cleaned regularly.
  4. Avoid keeping your goldfish together with snails.
  5. To help your goldfish maintain its bright colors, use a bright or light-colored background for decoration around your aquarium.

The longevity of your goldfish’s lifespan depends on your ability to pay special and close attention to its needs. Goldfish are generally considered low maintenance pets that can be easily gotten at the pet store, but they also have necessary needs that must be met.


Kelly Stanley