Why Is My Gourami Turning Black? (With 5 Easy Solutions)

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When I saw that my stunning blue and gold gourami had turned black overnight, I was a little freaked out. I ran to my local pet store to ask for advice – they told me that my fish might have experienced some trauma. Luckily, as the years passed, I learned what causes that issue and how to deal with it.

Gouramis typically turn black due to inappropriate water conditions, including elevated ammonia, nitrates, and nitrites. However, gouramis may also blacken due to an underlying disease, including fin rot, black spot disease, and Ichthyophonus. But In some cases, it is merely genetics.

As we proceed, I will elaborate on the different causes that turn gouramis black and show you how to identify the underlying cause. Then, I will list five simple steps that helped me deal with the situation in my tank. Hopefully, following these, your gourami will regain its colors within a few weeks.

Why Is My Gourami Turning Black?

Fish can change their colors for any number of reasons. Some color changes are slow, while others are quick.[1] With gouramis, it is usually a question of their mood and age. Some Gourami species (For instance, Honey Gourami) will become darker in color when they reach sexual maturity. 

Color changes can also occur during spawning.[2] But this natural change in color is not accompanied by adverse symptoms such as loss of appetite, lethargy, and timidity. If your gourami is turning black and their age and mating rituals are not the cause, you can probably blame one or more of the following factors:

1. Your Gourami Is Sick

Various illnesses can cause a gourami fish to change color, including:

  • Pseudomonas – This is a relatively common illness in dwarf gouramis. The infection has been traced back to a bacterium called Pseudomonas spp.[3] It causes lethargy, loss of appetite, ulcers, and the erosion of fins. The bacteria that causes pseudomonas can be found in most aquatic environments. 

It attacks weakened fish with a debilitated immune system. It can cause sudden death. One notable symptom of the infection is the dark spots on the sick fish’s body. Eventually, those dark spots will become red sores.

  • Fin Rot – Is your gourami turning black all over or just around the fins? If the fins are the only part of the body that has been afflicted, the creature probably has fin rot. The disease causes the fins to rot and fray. They will also darken. Additional symptoms include lethargy, loss of appetite, and inactivity. The fish might spend a lot of time sitting on the substrate.
  • Black Spot Disease – Black spot disease is caused by parasitic flatworms that dig into the fish’s skin.[4] You will perceive them as black dots on the gourami’s skin and fins. In many cases, black spot disease is unsightly but not necessarily harmful. Or, at the very least, the illness is unlikely to kill your fish.
  • Cryptobia Infestation – This parasitic infection is associated with a dark coloration in fish. Additional symptoms include labored breathing, loss of appetite, loss of scales, and mucus buildup.
  • Ichthyophonus – This pathogen causes a fungal infection that can darken the skin.[5]

2. The Wrong Tank Conditions

One of the most common causes of a color change in fish is stress. And few factors cause as much stress in fish as poor tank conditions. That includes water with the wrong temperature, pH, and hardness. It can also include overcrowding caused by overstocking and small tanks.

If you force your gourami fish to endure poor conditions in the tank, the discoloration is just one symptom among many that you may observe. Though, the exact nature of the discoloration may vary. While some fish will become darker, others may lose their color.

Another symptom of stressed gourami is when the fish chooses to lay at the bottom of the tank, as I discussed in this article. If you suspect that your tank is overcrowded, please check this article where I explain how many gouramis should be kept together.

3. The Ammonia Is Too High

Ammonia is not just a source of discomfort. It will harm your gouramis, killing them in the long run if you fail to take action. But before it kills them, ammonia will cause dark patches to appear all over their skin. The patches occur when the ammonia burns the skin, and then the skin heals.[6] 

Spikes in ammonia concentration can also harm the gills, affecting the gourami’s ability to breathe. Ammonia is not the only toxin that concerns aquarists with gouramis. You also have chlorine, chloramine, copper, lead, and the like to consider. But if your gourami has dark patches, ammonia is the most likely cause.

4. You Gourami Was Injured

Where the color of your gourami is concerned, injuries resulting from fighting or collisions with the objects in the aquarium can produce two side effects. First of all, the stress caused by these injuries can cause the gourami’s color to darken gradually. 

Secondly, the injuries can scab, forming black patches over time. It is also possible for blood to collect under the skin whenever the fish comes into contact with a point object, producing black dots and patches.

5. It’s Just Genetics

Some gouramis will turn black over time because of a genetic anomaly. This is a rare occurrence, and it is not a satisfying explanation for tanks with multiple gouramis that have started turning black. But it can happen from time to time. 

Suppose one or two gouramis in your aquarium are turning black, you have eliminated all the other potential causes, and the fish is still healthy despite the color change. In that case, genetics is the most likely cause.

What Should I Do If My Gourami Turned Black?

If the darkening of your gourami’s skin is not a natural occurrence, you can aid the fish by taking steps to resolve the factors responsible for the physical and mental stress and strain that caused the changes in color. That includes:

1. Improving The Aquarium Conditions

Start by improving the conditions in the tank. First of all, this will alleviate any stress the gouramis may have felt due to the poor conditions. Secondly, a well-maintained tank with suitable parameters will strengthen the gourami’s immunity, allowing the fish to fight off any infections and illnesses that might have caused the creature’s colors to darken. 

Please keep the following in mind:

  • Parameters – Test the water routinely. You have to keep the temperature, pH, and hardness within a range of 77 to 82 degrees F, 6 to 8, and 5 to 20dH, respectively. Make sure the ammonia and nitrites are around 0 ppm. The nitrates should be below 20 ppm.

To measure the pH, nitrates, nitrites, and ammonia, I personally use the API FRESHWATER MASTER TEST KIT (link to Amazon). I like this bundle because it lasts for hundreds of measures, turning it highly cost-effective. It also measures the parameters quickly and accurately.

I highly suggest keeping the tank clean. The easiest way to prevent diseases or to eliminate them is to clean the aquarium. Change the water weekly, siphon the gravel, and remove dead organisms. Otherwise, they will rot, causing the ammonia levels to rise.

Regarding temperature, I use the Cobalt Aquatics Neo-Therm Pro Aquarium Heater (link to Amazon), which I also reviewed here. This is the only device that keeps my temperature stable, which is extremely important when it comes to stress in aquarium fish.

  • Tank Size – You need at least 20 gallons for your gouramis. If you want to add more gouramis, you should get a bigger tank. Not only does a small tank induce stress, but it encourages the ammonia levels to spike at a faster rate. A big tank alleviates stress while also diluting the ammonia, allowing the aquarist to clean the tank before the toxin spikes.
  • Air stones – Oxygen-deficiencies are another potential cause of stress and discomfort. You can avoid oxygen deficiencies by adding water pumps and air stones. I use the Hygger Aquarium Air Stone (link to Amazon) in my aquarium, which is unbelievably quiet.

2. Treating Sick Gouramis

If you suspect that your gourami has a disease or infection, the first step would be consulting an aquarium veterinarian. Professionals will identify a treatment that can effectively tackle the disease. For instance:

  • Pseudomonas – Take a bottle of bitillin-5, place 1/6 of its contents in 10 liters of water, and then add the gourami for half an hour. Do this every day. You can also place the fish in a bath with potassium permanganate (0.5g in 10L). Consult a vet if you have questions about the exact amounts.[7]
  • Fin Rot – You can use API Stress Coat, Tri-Sulfa Tablets, and Melafix, to mention but a few.[8] I also recommend quarantining the fish to prevent the condition from spreading to other fish in your tank.
  • Cyptobia Infestation – You can treat this infection with Malachite Green, Nifurpirinol, and Furaltadone.[9]
  • Black Spot Disease – Place the fish in a formalin bath.[10] You can also use praziquantel. You have to clean the tank thoroughly to remove the worms. Otherwise, they will re-infect the fish.

In some cases, you have to quarantine the fish to prevent it from infecting its tankmates. You should do this if you haven’t yet identified the disease ailing the fish. But don’t forget to consult a vet, especially if you are new to gouramis.

3. Introducing A Few Plants

Include plants and decorations in the aquarium’s landscape. Some people only add plants when the gourami has an aggressive neighbor. Well, plants can indeed prevent unnecessary conflicts in the tank by allowing gouramis to hide from aggressive tankmates.

But gouramis in tanks with peaceful neighbors require plants and decorations as well. They don’t feel secure without hiding spots, regardless of whether or not they have a bully. By providing them with a sense of security, you’ll be able to fight underlying causes that turned your gourami black.

4. Feeding Your Gourami Properly

Give your fish a balanced diet that includes shrimp pellets, color flakes, algae rounds, live foods, frozen foods, etc.[11] Feed them once or twice a day. Give them food they can finish within two minutes. A proper diet (no overfeeding or underfeeding) will give them the strength to heal from injuries and diseases.

5. Picking The Right Decorations

Remove sharp objects that may injure the gouramis from the tank. You should also keep them away from faster, more active fish (such as barbs) that may annoy them. Surround your gouramis with peaceful fish such as danios, mollies, and platies. This will prevent unnecessary conflicts that may lead to injuries.

Will My Gourami Get Its Original Color Back?

Severe injuries and ulcers may produce dark patches that will never completely heal, at least not to the extent where the gourami’s color returns to its original shade in those areas. However, in most cases, a gourami fish will revert to its original color if you eliminate the illnesses and stress factors that caused the color change in the first place. 

That typically takes two to three weeks. At the very least, you should see improvement within that period, especially if you spend as much time cleaning and taking care of the tank as I discussed. If the situation doesn’t change, the underlying cause might be genetics.

Can Gouramis Change Color?

Some gouramis can change their colors. The most prominent example is the blue gourami, which is also called the three-spot gourami. It has black spots that fade when it is stressed. It will also develop a deeper blue hue during spawning. 

Other types of gouramis may change colors as well. As a rule of thumb, if gouramis darken or turn white, you need to deal with underlying causes by cleaning the tank and treating any disease or injuries causing stress. If this doesn’t work, consult a vet to ensure there isn’t an underlying genetic issue to the fish’s discoloration.

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Gouramis that turned black require your attention. Start by diagnosing the reasons for the ailment and treat the underlying cause. Gouramis are one of the most beautiful fish in an aquarium, but it is not uncommon for them to become damaged, especially when they experience diseases or injuries.

When your gourami turns black, you may want to consult a vet. I also suggest cleaning the tank thoroughly to remove debris and disease. You should also change your water if you suspect a water quality issue such as high nitrates or ammonia levels because it may have caused the fish to turn black.


  1. https://australian.museum/learn/animals/fishes/can-fishes-change-colour/
  2. https://petponder.com/gourami-fish
  3. https://www.thesprucepets.com/treating-pseudomoniasis-in-fish-5094501
  4. https://www.in.gov/dnr/fish-and-wildlife/wildlife-resources/wildlife-diseases-in-indiana/fish-disease/
  5. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/ichthyophonus
  6. https://pets.thenest.com/mean-goldfish-turn-brown-9425.html
  7. https://lifeoffish.com/dwarf-gourami-diseases-identification-treatment/
  8. https://www.petbarn.com.au/petspot/fish/medical-vet-services-fish/how-to-treat-prevent-fin-rot/
  9. https://www.fishbase.se/diseases/diseasessummary2.php?discode=359
  10. https://www.thesprucepets.com/black-spot-or-tang-disease-2920812
  11. https://www.aqueon.com/information/care-sheets/gouramis