Why Is My Goldfish Turning Black? The Complete Guide

A goldfish turning black can be a very disturbing sight. Once-bright colors covered in dark spots just don’t look normal.

But it’s important to investigate before panicking.

You see, there are several different causes for this. And not all of them are bad.

This guide will tell you why goldfish turn black, if there’s anything to worry about, and what you can do to help them (if needed of course).

Is this something to be worried about?

Goldfish are the quintessential “easy” fish to take care of. They are readily available at most pet stores and adapt well to life in your aquarium.

The most iconic feature of the goldfish is its shimmering golden color. This vibrant appearance is the product of thousands of years of selective breeding.

When a pristine goldfish suddenly begins to turn black, it’s easy to assume something is wrong. Color shifts to white are much more common than shifts to black. So when your fish starts to darken, it’s important to take the problem seriously!

Black color changes could be a sign that your fish is suffering internally. They might have a health issue that you need to address if you want your goldfish to continue living.

That said, not all cases of black color change are life-threatening or even dangerous. Sometimes color changes are completely natural for fish.

So how do you determine if your fish turning black is cause for concern?

You need to understand what is causing this change. You must learn to identify potentially serious symptoms and be proactive in providing care when needed.

Common causes

There are a handful of reasons why a goldfish may start turning black.

As we mentioned earlier, black color changes are quite rare among all types of goldfish. Thus, you will need to consider all possible causes to determine the best course of action.

Black is actually a notoriously unstable color in goldfish. Many pure black goldfish eventually lose their color and turn white or yellow. Watching a healthy goldfish go dark is incredibly rare.

As a result, most assume there is a serious health issue to blame. That may be the case, but there are also relatively innocent causes.

Here are some of the most common causes of a black color change and what you can do to care for your goldfish.

1. Ammonia in tank

Ammonia changes are, by far, the most common reason goldfish turn black.

Generally, the color change begins on the fins. Over time, it can gradually get worse and spread to the body. There it will appear as small patches of black skin that look burnt.

Author’s note: This is not a problem reserved for goldfish only. All species of light-colored fish can experience this.

Ammonia is a toxic chemical that is produced inside your aquarium. Most don’t realize it, but caring for fish in captivity is a constant battle to keep ammonia from building up in the tank!

That’s the whole point of the filtration and cycling system!

Fish produce ammonia through waste. Decaying plant matter and uneaten food can also cause ammonia spikes. Usually, aquarists can keep ammonia levels very low by simply cleaning the tank on a routine schedule.

Water changes are very effective in getting rid of the chemical. A powerful filtration system will also help. When the tank is not clean, ammonia levels can rise very quickly.

This chemical has the potential to kill fish. To make matters worse, the tank doesn’t need much to be lethal. Even a small concentration of 2 parts per million is enough to kill small fish like goldfish. Ideally, your ammonia levels should be 0 PPM.

A goldfish turning black next to a completely black goldfish

So how does ammonia cause a black color change?

Well, the chemical basically burns your goldfish’s skin. This is how ammonia kills fish. Higher concentrations burn the gills.

The good news is that seeing your goldfish turn black could actually be a sign that your fish is on the mend.

You see, it is impossible to see ammonia in water. You also can’t see when the chemical is burning your fish’s body. Black spots on your goldfish mean the body is healing.

This could indicate that levels have come down to a safer level. But don’t assume anything! Get out your test kit and check the water. Anything above 0 PPM should be cause for concern.

Author’s note: To help your fish, do more frequent water changes. Change about 20% of the water every week. Next, check your filtration system and make sure it is working efficiently.

Next, you’ll want to take a look at all the fish in your aquarium. You might see strange swimming patterns or labored breathing. These are telltale signs of ammonia poisoning. If you have a sick fish, move it to a quarantine tank.

Sick and stressed fish release a lot of ammonia. Unfortunately, high levels of chemicals only exacerbate the problem.

Check water conditions and remove dead plants or food scraps. You may also want to consider changing the way you feed the fish.

As a general rule, only provide enough food for your fish to eat in a few minutes (this can vary a bit by species of course). After that, remove any excess to make sure the ammonia levels don’t rise again.

2. Genetics

Now let’s move on to a more innocent cause. Some goldfish specimens are genetically predisposed to color changes. Although a goldfish turning black is rare, it is still possible!

“Mixed-breed” goldfish are the most susceptible to life changes. These are usually the cheapest goldfish you see on the market. They may already have strange coloring patterns on them.

These fish sometimes change color as they transition from juvenile to adult. This happens within the first year or two. Change is slow, you may not even notice it at first.

Goldfish may develop darker black spots on the body. This could be accompanied by the clarification of certain areas.

Author’s note: Some goldfish even go through major changes where their body takes on a brighter orange or yellow color!

“Purebred” goldfish from a reputable breeder may also turn a bit black. However, the change is usually much more subtle. You might see black streaks developing on the fins or small dark colored dots.

Either way, a goldfish that turns black due to genetics is nothing to worry about. This is completely normal and does not cause any health problems or a shortened lifespan.

3. Illness

Goldfish that turn black due to disease are rare, but it’s always a possibility worth mentioning. The disease in question is called black spot disease.

This is much more common in goldfish kept in ponds than in those kept in closed aquariums. The disease can also affect fish in the wild. Many anglers come across sick fish with this disease all the time.

So what is black spot disease? It is a parasitic disease of the fluke. Fish get it from infected water snails. Goldfish in ponds can also encounter the disease if bird droppings enter the water.

When fish have black spot disease, they literally develop spots on their bodies. Infestations can also vary widely. In mild cases, you might see a few spots here or there.

However, severe infestations can significantly cover goldfish in black.

Author’s note: These black spots are actually parasite eggs that burrow into the skin. Once inside the fish, the eggs turn into a hard black cyst for protection. Eventually, the spots will burst when the parasite is released (ew).

If you suspect disease is to blame, take a look at your goldfish’s behavior. The spots tend to be itchy, so the fish shake their bodies and try to rub against objects for relief.

To treat this disease, you need to remove snails from the environment. This can break the life cycle of the parasite. It takes time, but the fish will recover.

Although the disease looks horrible, it is considered less dangerous than ich.

Again, black spot disease is rare. Unless you keep your goldfish as an outdoor pond fish, your chances of encountering it are very low.

Can they return to their original color?

Goldfish that turn black may or may not retain their natural color. It all depends on the cause of this change and the prognosis.

If the black color change is genetic, your fish will remain so for the rest of its life! Although the change may not be what you expected, it will in no way affect your fish’s health or quality of life.

If your goldfish has turned black due to ammonia poisoning, the biggest concern will be whether or not your fish will pull through. The prognosis for severe ammonia poisoning is not good. In many cases, this is a fatal problem.

However, don’t assume your fish will die if the ammonia has peaked in the tank.

Remember that blackheads are the result of healing chemical burns. Watch your fish’s behavior closely. If swimming normally and perky, the goldfish may make a full recovery!

In this case, the spots will gradually fade. It takes time, but your goldfish will eventually return to its normal color. Just be sure to take the necessary steps to fix any ammonia issues to prevent future burns.

Now you have the right knowledge

You now have the knowledge to understand why your goldfish is turning black and if there is anything you need to do differently.

Seeing these beautiful fish darken over time can be sad at first. But often it’s just a natural phenomenon.

Assuming they are in good health, learn to appreciate this interesting color change. It’s all part of the fun!

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