Why Is My Goldfish Turning Black? Causes, Cure & Prevention

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Oh no! Why is my goldfish turning black? If you have a pet goldfish at home, watching it turn black can be a worrying sight indeed. The sight of your once brightly-colored fish turning into a darker, muddier color can be an unpleasant, if not downright scary sight.

However, if you find yourself in this predicament, know that there are many reasons goldfish turn black. Some of these reasons are actually harmless. So, before you begin to panic, it might be helpful to do a little investigation first!

In this article, we will thoroughly explore some of the reasons why goldfish turn black and what it means.

Should I be concerned if my goldfish turns black?

Shubunkin Goldfish, carassius auratus, Aquarium Fish

Yes, you should. A goldfish turning black may be a sign that something is wrong. There are several reasons why a goldfish may change its color, but not all of them are causes for concern. However, you need to err on the side of caution by taking this sign seriously.

First and foremost, goldfishes are relatively easy to care for despite their iconic colors and exotic appearance. Having undergone years of selective breeding procedures, there are hundreds, if not thousands, of goldfish species in the world.

Their versatility and hardiness as a species mean that when a goldfish turns black, something is wrong. However, there are several factors behind it, some good and some not so good. Let’s take a closer look at these factors!

Blending into its Environment

Beautiful goldfish in an aquarium.

The first reason we’ll address is one that is relatively harmless. Goldfish are adaptable creatures, and one of the most common reasons for a goldfish turning black is if it is in the process of blending into a new environment.

So, if you’ve just acquired a goldfish and placed it inside an aquarium with a dark background, black backdrop, or dark wallpaper, do not fret if your fish starts turning black!

Like most fish, goldfish have pigment cells embedded under their skin. Some of these cells produce a dark pigment known as melanin, which is what contributes to the black color found on the tails of most goldfish. This pigment also causes your fish to turn black in a dark environment.

Goldfish that are surrounded by darkness have a natural tendency to blend into its environment as a camouflage mechanism. To do so, its cells will produce more melanin, allowing it to turn black, blend into its surroundings, and hide from its predators. The melanin may cover the entire body or appear in patches around the goldfish scales, fins, or tails.

Solution: If you want your fish’s bright, gorgeous colors restored, change the backdrop in your aquarium to a much lighter color! Once you do this, the pigment will gradually wear out, and your goldfish will have its vibrant, sparkling color once again.


There are hundreds, if not thousands of goldfish species available as a result of cross-breeding. This extensive variety of goldfish breeds means each species will have its unique original color – often with no guarantees that these colors will remain permanent.

Many genetic changes take place within the first year of a goldfish’s lifecycle, which may indirectly cause its colors to change. So, assuming you buy a cross-bred goldfish that is only a few months old, its color may begin to change as it matures

Solution: There is nothing you can do if the changes are a result of genetics. Fortunately, the changes will not be life-threatening either, so you have nothing to worry about!

Ammonia Poisoning

One of the more harmful reasons your goldfish is turning black is also one of the most common. The number one reason goldfish turn black is due to ammonia poisoning.

Excessive ammonia in water poses a threat to your fish’s health by burning its gills and body. Unfortunately, excessive ammonia isn’t visible to the naked eye. Your best bet is to run your tank water through an ammonia test kit, and perform the necessary water changes immediately when your test kit readings indicate that something is off.

The good news is, black marks usually indicate that the ammonia burns are healing. Healing skin in goldfish is usually black and will return to its former color after it is fully healed. However, do note that some black patches may never return to their original condition due to extensive damage.

Solution: Cultivate the habit of cleaning your aquarium regularly without waiting for the fish to change color. Once you remove wastewater and add up to 60% of clean water, your fish will start healing, and you should see its skin return to normal.

Another solution is prevention. Test your fish tank regularly by removing uneaten food and fish waste. Finally, consider strengthening the biological filter in your tank. This way, you’ll maintain healthy ammonia levels consistently!

Black Spot Disease

The next factor we want to look at is black spot disease. If notice your goldfish developing black spots, it may be a result of black spot disease. 

One of the leading causes of this disease is keeping water snails close to the black goldfish or in the same tank with it. Bird droppings in ponds can also cause black spots, but if your aquarium is indoors and birds don’t have access to it, this disease will not break out.

Caused by parasites from eggs, plant debris, plant matter, and larvae by other organisms, it is very easy to know if your fish has contracted this disease as it will begin to rub its body against surfaces and flicker its tail constantly. It will also begin to develop black spots and cysts all over its body to protect itself from the parasite.

black spots on goldfish

The good news is, it is becoming increasingly rare for goldfishes to develop black spots due to black spot disease. This holds especially true for goldfish that are housed indoors. 

Solution: Avoid placing your goldfish in the same aquarium with other creatures because they are very sensitive. Your goldfish should be the sole landlord of the aquarium if you want to keep it safe. You can also use an aquatic parasite treatment to keep the water safe.


How often do you feed your goldfish? Do you feed it once, twice, or three times a day? This question is vital because when you drop excess food into the water, and the fish cannot finish the leftover food, the rotting food will contaminate the water.

Excess food droppings may also clog the filtration system, which will disrupt filtration efficiency. This may lead to black spots and ammonia poisoning, as discussed above.

Solution: Only feed the fish what is necessary. The size and species will determine how much it can eat. Don’t feed your goldfish more than what it can consume! Proper feeding will keep your aquarium clean, and by extension, the fish healthy. Also, cultivate the habit of removing uneaten food immediately.

Illness and Stress

A view of a golden fish in a bag isolated on white background

Like humans, goldfish respond to stress and illness. In response to these negative stimuli, they may develop black spots all over their fins and scales. Besides black spot diseases, some other illnesses may arise if the fish is uncomfortable with its surroundings.

A change in environment may lead to stress and illness. Also, if you introduce a new fish species into the aquarium, this may cause the fish to fall ill. Stress could also result from an extended trip, especially if the fish were shipped to you from afar.

Solution: If your goldfish has developed a health issue, watch it closely. If stress is the cause, your goldfish will regain its natural colors over time.

If it is caused by rising ammonia levels, constantly changing the water and removing waste will positively affect your fish’s pigment cells, and black patches will wear out gradually.


Will All Goldfish Change Color? (Comparing Different Scale Types)

One question many goldfish owners ask is whether their pet will change color, or if all goldfish change color. To answer this question, you first have to understand why goldfish change color.

The scales, pigment, and several other factors, some of which we discussed above, are responsible for changing colors in goldfish. However, the scales type also plays a major role.

Goldfish have different types of scales. The scales determine how and when the colors change if they do. Let us look at the three key types of goldfish scales.

  • Metallic Scales: Metallic scales have what we call crystalline pigments that are also called guanine. Guanines contain a high dose of xanthophores and erythrophores. These cells are responsible for the orange, yellow, and red colors found on the scales of the fish. If your goldfish has metallic scales, it may likely not change much during the course of its life.
  • Matt Scales: Goldfishes with Matt scales generally lack guanine and pigment cells. As a result, they are mainly pink light greyish color, cream-colored or white, or a mixture of all these colors. If your goldfish has a matt fin. It will not change its color at all.
  • Nacreous Scales: Another scale type is the Nacreous scale which also contains some atoms of guanine but on a moderate level. Goldfishes with nacreous scales have a pearl-like appearance depending on the density of the guanine on the scales. Fishes with this type of scale may appear translucent, and they usually have a yellow, red, or black color. A goldfish with this type of scale will usually change its color over time.

Will Black Spots On Goldfish Go Away?

Large Oranda Goldfish in aquarium

This will depend on the type of scales it has. Besides the scales, several other factors, as discussed in this article above, will determine whether the black spots will go away or not.

If the black spots are a result of a dark environment, the black spots will remain until you change the color of the background. If it is caused by ammonia poisoning, the spots will not leave until the water is changed constantly.

Even so, if the damage to the fins and scales is severe, the spots may never clean off. Feeding the fish in the right proportion and cleaning the aquarium regularly are some easy preventative measures you can take to stop black spots from ever developing in the first place.

What Are the Signs That Your Goldfish Is Dying?

In a situation where the fish is dying due to ammonia poisoning, poor health, or infestations, knowing the signs to look out for is crucial to saving its life. If your goldfish is dying, it will exhibit some of these characteristics.

  • Rapid inhaling and exhaling
  • Lying at the base on the goldfish tank
  • Erratic swimming
  • Rubbing its body against hard surfaces
  • Torn or folded fins
  • Lack of appetite
  • Milky white patches
  • Ragged appearance
  • Protruding eyes
  • Pale gills
  • Bloating


If you notice any of these signs, do not be quick to conclude that your goldfish is dying; however, a combination of some of these signs means that something has gone terribly wrong. In such an event, make sure you feed the fish with the right feed and practice quality hygiene.

Do not overfeed the fish, and make sure you remove uneaten food from the tank. Also, clean the tank regularly by changing at least 60% of the water regularly. A water change once every 10 days is a good practice.


Goldfishes are pleasant pets, as they beautify the home and make it more appealing. Unfortunately, their beauty is sometimes diminished when black spots form on their fins and body.

If you want your pet to live for many years in good health and all its vibrant glory, follow all of the solutions highlighted in this article to create a healthy environment for it. However, if the dark spots are appearing as a result of genetics, there really isn’t anything you can do about it.

Did you enjoy this article? Don’t forget to share it with a fellow goldfish enthusiast who might benefit from it! 

Wanda is a second-generation aquarist from the sunny tropics of Malaysia. She has been helping her father with his freshwater tanks since she was a toddler, and has fallen in love with the hobby ever since. A perpetual nomad, Wanda does her best to integrate fish-keeping with her lifestyle, and has taken care of fish in three different continents. She loves how it provides a nice break from the hustle and bustle of life.

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