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Should Koi Have White Patches on Their Skin?

Should Koi Have White Patches On Their Skin

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Koi are beautiful fish with recognizable patterns. They usually come in orange, red, yellow, black, and white. But, when strange white patches start to appear on your koi’s skin that is clearly not a part of their usual pattern, you may begin to wonder if you’ve failed to take proper care of your koi fish. This frequently raises the question, “Should koi have white patches on their skin?”

Koi should not have white patches on their skin, apart from their natural white patterns if they have them. White spots on koi are signs that they are ill due to poor pond maintenance, allowing parasites to thrive and then find their way to your koi fish to feed on. In this article, we’ll introduce the common parasites that cause white patches on koi skin and what you can do to treat the condition.

White Spots on Koi

White Spots on Koi

White lumps may be a sign of fungus on koi. The white patches may also be a sign of bacterial infection. Here are common parasites that cause white spots to appear on sick koi fish.


White patches on koi skin are commonly attributed to the ich or white spot disease. This disease is common among tropical fish but can infect pond fish just the same. Ich is a ciliated protozoan or a parasite with hair-like structures called cilia. They grow in the pond and then attach themselves to your koi’s gills. This can lead to fatal complications, especially among your smaller fish.

Ich parasites begin as hatchlings from cysts at the bottom of unmaintained ponds. They use their cilia for swimming around the pond, looking for a host. They will die unless they find a host within two days of hatching. When they find a koi fish to attach to in time, ich will appear as small white grains of salt on your koi’s skin.

The ich feed on your koi’s tissues for about three weeks after attaching and digging into their bodies. Later on, they will detach themselves from your fish to reproduce at the bottom of the pond, repeating the parasitic cycle.

Ich can be deadly to smaller koi fish because of how the parasite attaches near the gill area. If you find smaller fish constantly gasping for air near your pond’s surface in addition to white spots on their body, this may be a sign of ich parasite infection. If left untreated, your small koi may die and then cause other bacterial infections.


Another protozoan parasite that might explain the white spots on your koi is the trichodina parasite. Infected koi may have white or gray-white patches on their body, confirming the presence of this parasite.

Like ich, trichodina have structures they use to swim around your pond water. Instead of cilia, they have hooked flagella or thread-like structures that can get through your koi’s mucus layer and then dig into their tissue.

Koi fish have mucus layers typically to protect themselves from bacterial infections. Mucus layers may get damaged when the protozoa and other bacteria already exist in the water from the beginning. Constantly touching your koi may also damage their mucus layer.

Trichodina thrives in warm waters. This parasite can survive longer than ich without a host to feed off of. Once they do find a koi host, they attack its skin and gills, causing the fish to exhibit flashing or swimming in sudden bursts. This behavior is a way for fish to scratch themselves but they may also exhibit symptoms of rubbing against pond walls. Constant flashing may cause infected fish to appear lethargic.


It is possible that the white spots on your koi fish are a sign of columnaris infection or cottonmouth disease. You might think columnaris is a fungal infection because of the way it appears like mold on your fish. However, columnaris is a bacterial infection due to a rod-shaped bacterium known as Flavobacterium columnare.

This bacterium thrives on organic waste and is a common pathogen among freshwater fish, so your koi are naturally susceptible to columnaris disease. Columnaris will appear as white threads on your koi’s mouth, thus explaining why it is also known as cottonmouth disease.

Infected koi fish may develop soggy bellies and slimy skin due to a damaged mucus layer. Columnaris may also make your koi’s skin around its gills appear dry. This might make your koi swim up to the surface to gasp for air regardless of how many air stones you have set up in your pond. Your koi’s trouble breathing may indicate that it has contracted this bacterial disease.

White Spot Pond Fish Treatment

White Spot Pond Fish Treatment

You might have gathered that the common issues that cause white spots in your koi are parasites and bacterial infections. These microscopic organisms thrive in specific water chemistry, indicating that your pond may be in poor condition.

As soon as you find the slightest sign of white patches on your koi’s skin, consider keeping the infected fish in a holding tank to avoid spreading the disease further. If your koi fish have either ich or trichodina parasites, you must increase the salinity levels (0.5%-0.6%) of your quarantine tank and isolate them for five days to two weeks, depending on the severity of your koi’s infection.

Sometimes, parasites develop immunity to increased salt levels. In such cases, you may have to include formalin or malachite green. These organic compounds are effective against harmful protozoans and are available from your usual koi supplier.

If your koi’s white spots are due to cotton mouth disease, you will have to isolate the infected fish and then treat them with antibacterial medicine. You may also treat the water in their isolation tank with potassium permanganate. This treatment also helps against trichodina parasites.

While treating your fish, you may want to conduct maintenance for your main pond as well. If you notice that salinity, temperature, or pH levels are amiss, you must adjust accordingly to ensure no protozoans or bacteria propagate further.

Final Verdict: Should Koi Have White Patches on Their Skin?

Healthy koi fish should not have white spots or patches on their skin, which are signs of illness due to bad water chemistry. Common parasites that cause white spots are ich and trichodina. Meanwhile, columnaris is a bacterial infection that resembles white spots on your koi’s mouth and skin. If you find any of these white patches on your koi, which may start off as small as white salt grain-sized spots, you should immediately isolate your infected fish and conduct pond maintenance to avoid the parasites infecting your other koi fish.

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