Goldfish Turning Black – Why and How To Prevent It?

Goldfish have been known for their distinctive gold and orange color. Other species of Goldfish can be of different colors, like black. However, if a gold or orange Goldfish changes its color to black, it can worry the owner. The question is whether this change in color is harmful to your Goldfish or not. It all depends on what has caused this color change. This article will help you understand this change in your Goldfish better.

Goldfish turning black is a phenomenon that can occur in both pet and wild goldfish. It refers to a change in the color of their scales from gold, orange, or white to black or dark brown. There are several reasons why this may happen, including genetics, environmental factors, and health issues. While a change in color may not always be a cause for concern, it is important to monitor your goldfish’s behavior and consult a veterinarian if necessary.

If you have recently observed a shift in colors in your Goldfish, with black patches appearing and growing to the entire body of your pet, you must be wondering why that is happening. There are many reasons that could lead to this color change, but not all of them are harmful. Some could be indications of a bigger problem, while others can be completely harmless.

Reasons why your goldfish has turned black?

Out of the many reasons that can cause the color shift in your pet Goldfish, we will start with the potentially harmless ones, moving on to the dangerous ones.

Reasons Why Your Goldfish Has Turned Black


One of the leading reasons is simple genetics. Crossbreeding among fish and Goldfish can not only create fancier and more beautiful species but also pollute their original gene pool. An orange Goldfish, having pure orange genetics, when crossbred with a different specie of Goldfish, such as the black moor, gives rise to a 50% chance of their offspring being of mixed color. Now when these offspring further reproduce, there is a high possibility that the Goldfish born are gold or orange in the beginning and turn to black when they age. The reverse is also likely.  

Generally, you will know the true color of your Goldfish once it has fully matured. The genetic color changes will occur at the age of about 1 year in Goldfish. Your Goldfish may only develop a few black patches, or in some cases, the entire Goldfish can turn black. There is no guarantee as to what will happen, but what you can be sure of is the fact that this change is completely harmless.


Why are leopards colored the way they are? Why are sparrows so brown that you can hardly spot them on the bark of a tree? The answer is simple: camouflage. Even in unhostile environments, animals are likely to camouflage just to fit into their environment better. It is likely that your Goldfish is turning black to fit better into its surroundings, especially when it is kept in a poorly lit tank. Some aquariums have a black backdrop that can reflect a dark ambiance for your Goldfish, causing them to change colors to blend well.

In some cases, especially in outdoor ponds, where your Goldfish are at high risk of being preyed upon, Goldfish develop melanin to turn darker in color. This keeps them relatively safer as compared to being bright orange in color, which makes them easier to spot. Your Goldfish has its own survival instincts and turning black may be one of them.


Just like humans, when a Goldfish is injured, the platelets in the Goldfish’s body help develop a scab on the injury. For us, this scab is red or maroon in color, but for Goldfish this scab is black. If you observe certain black patches on your Goldfish, especially after it has been in a fight, the black patches must be the scabs. These black scabs suggest that your Goldfish is up and about on the journey of healing and there is nothing to worry about.

Stressed Out

There is a high chance that unfavorable conditions in your Goldfish tank cause the color change in your Goldfish. Sudden changes in temperature and pH, can cause your Goldfish to become stressed. Black patches may appear on your Goldfish to combat these frequent changes.

Ammonia Burns

It is common knowledge that ammonia and nitrites in your Goldfish tank are extremely harmful to your Goldfish. High levels of ammonia can cause the skin of your Goldfish to burn and scathe. Once these burns start to heal, blackish scars develop on the Goldfish. If you observe inflamed blood vessels in your Goldfish, combined with swollen gills, your Goldfish may be suffering from ammonia poisoning. An ammonia test can confirm this. But if your Goldfish has started to develop black patches, it has already started to heal. The black patches are an indication of a recovering Goldfish, but also an indication that the water conditions in terms of ammonia levels are not favorable in your Goldfish tank.

Ammonia Burns

Black Spot Disease

Probably the most dangerous of all the reasons behind your Goldfish turning black in color is the black spot disease. As the name suggests, this disease causes black spots to form all over the Goldfish’s body. This disease is more common in outdoor tanks, and ponds, where the chances of other animals coexisting with your pet Goldfish are high. Snails and bird droppings in outdoor ponds give rise to the parasite that causes this disease.

Black Spot Disease

The parasite latches onto the skin of the Goldfish and slowly enters the body. After entering the Goldfish’s body, this parasite begins to reproduce. Black spots emerge on the skin of the infected Goldfish, which erupt to release the reproduced parasite. This disease can greatly affect the health and appearance of your Goldfish, and care must be taken to avoid it. If you observe that lately, your Goldfish has been rubbing its tail with the plantation or the walls of the tank, it is possible that it is trying to relieve itself from the itch that the black spot disease is causing it. This is one good way to spot this disease, apart from the visible black spots.

Fixing the problems that give rise to your goldfish turning black

As troublesome as the reasons behind your Goldfish turning black sound, they each have a relatively easy solution. However, if your Goldfish has been changing color as per its genetic code, there is nothing you can do to fix it. as for the other issues, here is what you can do:

Keeping Ammonia Levels Low

Ammonia burns can not only alter the appearance of your Goldfish, but they can also be extremely deadly. To avoid the accumulation of ammonia and nitrites in your Goldfish tank, you must clean your tank regularly. It is best to change the water in your Goldfish tank once every two weeks, but if you have a lot of Goldfish, it is best that you do so weekly. Uneaten food and waste decay and give rise to the ammonia levels in the tank. For this reason, you must never overfeed and overstock your Goldfish. Leftover food must be removed from the tank as soon as the Goldfish stop eating. Ideally, you should test the tank water once in a while for ammonia levels, which will keep you aware of the ammonia and nitrite situation.

Products for Slime Coat

Your Goldfish may be prone to infections, burns, and injuries if their slime coat is not very strong. The slime coat of a Goldfish is essentially what keeps it safe from minor injuries and pests. To maintain the strength of your Goldfish’s slime coat, you can use off-the-shelf available products such as the API Stress Coat and the StressGuard Slime Coat.

Lighter Backdrop

Changing the environment of your Goldfish from dark and gloomy to bright and lit can also help eradicate the problem. Once your Goldfish that has been developing melanin to fit well into its surroundings, and observes the change in the ambiance, the melanin production will decrease. The black patches may even reverse if they are caused by melanin and are an effect of a dark environment. However, make sure that you bring about these changes gradually and not suddenly. The sudden shift in the surroundings may stress out your Goldfish, making them ill.

Isolation From Outdoor Species

 If your Goldfish has developed the black spot disease, it is best to isolate your Goldfish from snails and other organisms that may be causing the parasite to grow. Keeping your Goldfish under close observation is the best way to eliminate the parasite. If one or some of your Goldfish are infected, you must quarantine them to avoid the spread of the disease. You will observe that like any other ich, the black spot disease will soon begin to die off as the parasite does not find a new host to reside and grow in.

Reversing Back to Original Color

It may sound impossible, but it is highly likely that once the conditions are favorable for your Goldfish, it may start to reverse back from turning black. As long as the change to black color has not been happening as per genetics, your Goldfish will start to turn back to being gold or orange.

Reversing Back to Original Color

As for Goldfish who are genetically bound to switch colors, you can never truly tell what color your Goldfish will be when it is still in its growing stages. After your Goldfish has fully matured, you will observe the color changes in it. These changes can be sudden or can keep happening throughout the Goldfish’s life.

The Bottom Line on Goldfish Turning Black

The highly distinctive feature of a Goldfish is its color. As appealing as the black species in Goldfish may be, it is puzzling to observe the switch in a Goldfish’s color from its distinctive gold to black. Some changes can be reversed, but some you and your Goldfish will have to stick to forever. Who knows, maybe those black patches here and there actually look good on your Goldie, maybe those patches are what make it look rather spectacular.

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