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can molly fish change colour

Can Molly Fish Change Colour?

Maybe you have recently been to a pet shop, found some adorable pure white baby mollies, and decided to take some home. But after a week or so of them being in the tank, you start to notice the fish developing black patches.

Is it possible for molly fish to change colours, or is it a sign of an underlying health condition? 

Molly fish can change colour as they grow older or when exposed to stressful conditions. Colour changing can either be a natural process or a result of the stress hormones produced when their environment changes or a new fish is introduced.

Keep reading to learn why colour changing in molly fish occurs and if there’s anything you can do to prevent or encourage it. 

Molly Fish Can Change Colour Due to Ageing or an Illness

It doesn’t necessarily mean a bad thing if you notice your molly fish changing colour. It may just be ageing. But it’s also important to make sure that your fish is healthy because diseases can also cause colour changes in Molly fish.

The following discusses the colour change in Molly fish in more detail. 

Ageing Can Cause Colour Change in Molly Fish

The main reason Molly Fish’s colour will change is natural ageing. Baby fish will typically have very dull colours compared to adults, and their patterns often won’t appear in full until the fish reaches maturity.

One of the most common instances where you’ll see a colour change in Molly Fish is if you buy your Molly Fish when it is only very young. They’ll typically come to you a relatively dull colour, although it should still resemble the adult colouration, and over time that colour will come in more strongly. 

The best example of this happening tends to be with Dalmatian Mollies. Dalmatian Mollies are known for their bold black and white spotted pattern. However, they’re not born like that.

I have a Dalmation Molly in my tank. She is the mum of the tank and has the very well thought out name of…Molly! 

Like actual Dalmatian puppies, baby Dalmatian mollies start off as a dull white or grey colour. It can make them pretty hard to pick out of a tank of mixed mollies because they won’t have any real identifying features.

As the dalmatian Mollies begin to grow, you’ll notice their colour changes, and black speckles will begin to form. If you’re not aware that you have a dalmatian Molly, this can be a pretty scary experience because black specks or darkening fins and scales are often a symptom of a disease. 

Diseases Can Cause Molly Fish To Change Colour 

If your fish suddenly begins to change colour, then the most likely reason that your fish’s colour has changed is that they’re suffering from a disease. The most common illnesses that’ll change your fish’s colour are fin rot and white spot disease.

I’ll discuss white spot disease in a later section of this article, so let’s focus on fin rot for now. 

Fin rot is typically a fungal condition that occurs because of poor water quality, usually combined with a previous injury. It tends to happen when some damage occurs to your fish’s fin. Then because of poor water quality, a fungal or bacterial infection will set in.

The first symptom of this is that your fish’s injury isn’t healing, or it’s actually getting slightly worse. That’s when you’ll start to notice blackening around the edges of the injury, as well as pieces of the fin beginning to rot away and fall off. 

As with all colour changes, sometimes it can be difficult to determine whether or not it’s a problem or a simple colour change. To decide whether or not it’s fin rot, you’ll want to look for one main thing, whether or not the injury to the fin is getting worse. 

If the fin is healing from the injury or looks completely fine, you’re probably not dealing with fin rot. You could still be dealing with an ammonia burn, but that should heal just fine with hygienic tank conditions.

What Colours Can Molly Fish Be?

Molly Fish can be in various colours. Over 43 types of Mollies are officially recognized up to now. However, with all of the individual variations that these fish can have, your rainbow of Mollies can appear even more diverse.

Mollies can have 3 primary pigments: black, orange, and white. The colour varieties and patterns come from these 3 main pigments, just with different dilution and intensifying genes.

Do Molly Fish Lose Their Colour?

Molly Fish can lose their colour when placed in stressful situations. They can also lose their colour as they get closer to the end of their lifetime. More energy will be put toward maintaining other bodily functions and less toward their pigment.

When you look at tropical fish guides online, they state that one of the most obvious symptoms that a fish is suffering from some ailment is that its colour begins to dull or darken. Some varieties of fish, like bettas, will even get stress stripes. 

If you add a new tank mate or decor to your Molly’s tank, then their colours may begin to dull as a stress response. It’s also especially common after shipping, so if you get your new Molly in the mail and it seems to be a duller colour than it was online, make sure you give it a few days before judging it. Just when you think you’ve been given the wrong fish, its colours will often brighten up just as soon as it has settled into its new environment.

Another common situation that fish will lose their colour is when they’re suffering from a disease, in poor health, or simply just unhappy in an overcrowded pet shop fish tank. I’ve often had the experience of purchasing a betta or some other fish from a pet shop thinking that they were one colour, only to have their colour change significantly after a few months of a good diet and tank conditions. 

Why Does My Molly Fish Have White Spots?

Your Molly fish may have white spots because you likely have a Dalmatian Molly, or your fish could be suffering from Ich. Dalmation Mollies naturally have a pattern that’s speckled with white and can be mistaken for Ich or vice versa.

Sometimes, you won’t initially notice when you purchase a Dalmatian Molly. That’s because in stressful situations, as most pet stores are, or when the fish are young, the dalmatian pattern isn’t as visible. As it begins to appear more clearly, you may start to notice bright white specks on your fish’s body.

Fortunately, this isn’t a cause for concern in the case of a Dalmatian Molly. It’s simply the fish’s natural pigmentation coming through.

However, you need to pay attention if your fish (that you didn’t purchase as a dalmatian Molly) starts to show white spots or specks. Yes, it could just be some natural colour variation coming through, but it could also be Ich, also known as white spot disease.

Ich Can Cause Molly Fish To Act Oddly

Ich is a highly contagious fish disease that’s caused by a parasite. It tends to attack fish when they’re already weakened, so purchase and shipping is the prime time to acquire the disease.

It can be pretty hard to identify Ich, especially if you have a white fish or a fish with some white colouration. But there are a few telltale signs you can look for, including changes and behaviour and the appearance of the spots.

Ich has a relatively long life cycle, which is one reason it’s so hard to eradicate, but because of that, it can also be hard to spot, especially if it’s in one of the non-visible life cycle stages.

In Ich’s first stage, the parasite will enter the fish’s body and move around beneath its skin and tissue, feeding on their cells. In this stage, you’ll be unable to see any visual expression of the Ich, but you may notice that something is wrong with your fish’s behaviour. Typically, your fish will start swimming around with clamped fins, and they may also begin to rub up against any ornaments in your tank.

After the parasite has matured, it’ll turn into a hardened cyst to be released from the fish’s body to return to the substrate and restart the life cycle. This is the stage that you can see Ich in. It should appear like tiny white specks on your fish’s body. It’s what can make it hard to identify. After all, if your fish naturally has white specks, how are you supposed to distinguish the Ich specks from the natural colouration?

Ich specks are typically around the size of a grain of salt, smaller than most speckles that you’ll see on your fish. They’re also matte, while fish scales are typically shiny. Plus, they spread. 

When you first notice the specks take a good look at your fish, maybe even some pictures. Then a day or two later, you can recheck your fish to see if there are more specks than before. If more specks are present, chances are your fish is suffering from Ich. 

Do Black Molly Fish Change Colour?

Black Molly fish can change colour over time. Their black pigment can conceal many other colours, so if yellow or white starts to peek through, they’re not changing to a new colour. They’re just revealing more.


Molly Fish can change colour over their lifetime or due to a traumatic event. Over time, the amount of pigment in their bodies can change, revealing hidden colours or covering previously visible ones.

Their colour change can also occur due to stress during an illness, rehoming, or when introduced to a new tankmate. It’s essential to know the symptoms of common fish illnesses so you can identify when it’s a simple colour change or something more serious.

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