why is my molly turning black

Why is my Molly Turning Black?

Mollies can turn black for any number of reasons. This isn’t always a cause for concern. For some mollies, this change is merely cosmetic, that is to say, it doesn’t mean anything where the molly’s health is concerned. For other fish, this drastic color change is a sign of trouble. You have no way of determining the seriousness of the issue until you identify the potential causes, which can include:

1). Genes

Some mollies are genetically predisposed towards this color change. This is especially true for dalmatian mollies[1], a variation of the sailfin molly. Some dalmatian mollies are white or dull grey at birth. But as they mature, they develop dark spots. Over time, those dark spots may spread until the fish becomes completely black.

It is a common occurrence that confuses some amateur aquarists whilst annoying others who purchased their dalmatian mollies specifically because they appreciated the white or dull grey colors.

2). Fin Rot

If your molly’s fins are the only organs turning black, it probably has fin rot. Sometimes, this color change is subtle, only becoming apparent when the fins begin to fray. The bacterial infection will eat away at the molly’s fins, making them shorter and shorter until they are gone.

Fin rot is primarily caused by poor water quality, overcrowding, and overfeeding, not to mention poor handling.

3). Ammonia

[2]Whenever goldfish turn black, aquarists test for ammonia, and for good reason. The toxic substance is a danger to fish, harming their gills, and compromising their ability to breathe. Produced by decaying plants, leftovers, and fish waste, ammonia can burn the skin of a goldfish.

Though, surprisingly, the black patches on their skin are encouraging. They are a sign that the goldfish has started healing. In other words, you cannot see the burns left by ammonia on the skin of your goldfish, only the consequences of the healing process.

Obviously, mollies are not goldfish. However, goldfish are not the only fish whose color can change as a result of environmental conditions such as ammonia spikes. Color changes in fish are governed by a branched cell called ‘Chromatophore'[3].

Whether a fish darkens or pales depends on the distribution of the color pigment in the chromatophore. Poor water conditions, including an elevation of ammonia, nitrate, and nitrite levels, can cause the color pigment to concentrate in a cell. As a result, the fish will become darker. Though, it can also become lighter. Similar consequences can manifest as a result of the wrong pH and hardness.

4). Black Spot Disease


Also called fluke disease, black spot disease has been traced back to larvae that grow in the intestines of a bird. The larvae eventually reach the water via the droppings of the bird. They mature and infect snails before developing further and making the leap to fish. When these parasites settle under the skin of fish, black spots appear.

Birds are infected by these parasites when they eat diseased fish. You can introduce black spot disease to your molly fish tank through infected snails.

5). Stress

You wouldn’t expect stress to cause a reaction as drastic as a change in color, and it doesn’t. Stress doesn’t cause mollies to turn black. However, it can affect their eyes, causing them to darken.

Studies that were done on guppies[6] and tilapia[7] found that their eyes could darken in response to aggression and trauma. Scientists don’t know for certain how stress changes eye color. But they have enough evidence on record to prove that it happens.

And considering the many similarities between guppies and mollies, it isn’t that inconceivable for your molly’s eyes to darken as a result of stress.

How to Treat Mollies That Turned Black?

You cannot treat a dalmatian molly that has turned black, not if the change happened naturally as a result of the creature’s age. But if the transformation in your molly’s color was instigated by an external factor, you can try the following treatments:

1). Fin Rot


Because fin rot is often caused by poor tank conditions, you should start by carrying out a water change and improving the conditions in the tank. Once this is done, you can treat the fish with antibiotics. Ask a vet to recommend an effective product. You can also add aquarium salt to the tank. It will enhance the healing process.

2). Ammonia

Test the water to confirm that the ammonia concentration is too high. You should also test for chloramine, a combination of chlorine and ammonia. Some places use chloramine to treat tap water. If you get your tank water from the tap, you can use commercial products (such as No-Ammonia) to remove chloramine[9].

If ammonia is your only concern, you should identify and then combat the factors elevating its concentration such as overfeeding and poor filtration systems. You should also perform a partial water change along with lowering the pH. Many aquarists use pH control products to neutralize the ammonia[10].

3). Black Spot Disease


Because black spot disease is typically introduced to aquariums via snails, you can cure a molly fish infected with the disease by removing the snails. Black spot disease is less dangerous than ich, and it rarely kills its victims. Some people use mild antibiotics to treat it. But a molly fish can recover from the disease on its own in the absence of antibiotics.

4). Stress

The easiest way to combat stress in your fish is to keep them in a well-maintained tank. Mollies are peaceful fish that should be kept with equally peaceful fish. [12]They need temperatures ranging from 78 to 82 degrees F, a pH of 7.0 to 8.0, and hardness ranging from 10 to 25 DGH. You should rear them in tanks of at least 20 gallons to avoid overcrowding.

Because of their enthusiastic breeding habits, you should always keep two to three females in a tank for every male molly fish. This will prevent the males from harassing the females to death. A molly fish living in a clean tank with the right tank mates and appropriate parameters is less likely to suffer from stress, especially if it has plenty of plants and decorations in the aquarium.



2- https://www.aquariumsource.com/goldfish-turning-black/

3- https://www.fishscience.co.uk/faq/fish-colouration/

4- https://en.wikipedia.org/wiki/Black_spot_disease_(fish)

5- https://www.adfg.alaska.gov/static/species/disease/pdfs/fishdiseases/black_spot_disease.pdf

6- http://www.jolyon.co.uk/research/publications/Heathcote%20et%20al%20Dynamic%20eye%20signal.pdf

7- https://scienceilluminates.com/2014/04/09/your-fish-has-dark-eyes-it-might-be-stressed/



10- https://www.thesprucepets.com/ammonia-poisoning-1378479



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