How to Treat Koi White Spot Diseases (Causes & Treatments)

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Guide to Identifying White Spots & Best Koi White Spot Treatments (Updated)

how to identify koi white spot disease
Several diseases can display symptoms of white spots in koi, so it can be difficult to figure out the exact cause.

Although there are a large variety of different diseases in koi carp, often times symptoms can present in very similar ways, making it difficult to identify the root cause. One symptom in particular is white spots on the body, fins, and gills of koi, which tend to appear as a primary symptom in a range of different diseases. In fact, we can’t think of another symptom that confuses more fish keepers in the hobby, as not only are the white spot diseases visually similar, they are often accompanied by similar sub-symptoms, such as loss of appetite and dulling of color.

The best way to identify the cause of your white spot symptoms is to inspect the spots more closely, as although they can be very similar on first inspection, most spots will have slight variations in appearance. For example, in cases of ich, the white spots would be very small, tough, and evenly distributed (not clumping) across the body of the fish. However, in cases of pox, the white spots may be larger, softer, and may clump together in random patterns and groups. Identifying the differences in appearance and observing how the spots spread are the easiest ways to distinguish between diseases in the early stages.

Here you can find a brief overview of the most common causes of white spot symptoms in koi and the best treatment options. For more  detailed information, please refer to each topics dedicated article at the bottom of each section.

1) Koi Ich (Small, hard, white spots)

koi with small fuzzy white spots ich
Ich presents as white small spots over the body of the fish which look like grains of sand.

One of the more common causes of white spot symptoms in koi is the parasite Ichthyophthirius Multifiliis, or “ich”, for short. This stubborn parasite is a particular nuisance for both fresh water and salt water fish, and can be difficult to treat due to its very rapid life cycle. Ich presents as small white spots on the body, scales, fins, and gills of fish, which can eventually grow in number to resemble grains of sand. The small spots are actually the parasite itself, feeding from the fluids contained in the top layers of skin tissue. This stage in its life-cycle is know as its encysted stage, and during this period it’s protected from treatment with a hard outer shell. Although not initially dangerous, the parasite becomes a huge problem if left to spread, as its reproduction cycle is extremely aggressive, and it can very quickly take over an entire pond. Mortality rates are high when ich is allowed to spread to other parts of the fish, particularly the gills, where the damage to tissue leads to respiratory problems and secondary infections.

Small white spots that look similar to grains of sand are a tell-tale sign of ich, but your fish may also have other symptoms, such as a loss of appetite, rubbing behaviour, or hiding away from the rest of the fish. Common symptoms of Ich are below:-

Koi Ich Symptoms:

  • White spots that resemble grains of sand
  • Itching or rubbing against the pond
  • Less interest in feeding
  • Shyness and swimming alone
  • Hiding under shelters
  • Lack of color & dull appearance

How to Manage & Treat Ich Symptoms 

Being an ectoparasite (external), ich should be easy to treat, but the problem is ich’s rapid life stages and the fact you can only treat the parasite while it’s seeking new hosts. During its white spot cyst stage, the parasites are protected within their hardened outer shell. However, to reproduce the parasite needs to leave the host and enter a reproductive stage, which then creates more free-swimming infectious parasites. During this stage in the parasite’s life cycle it can be treated, and it can also be sped up by increasing water temperature. The ich parasite’s life cycle is highly dependent on the surrounding water temperature, with higher temperatures increasing the rate of reproduction. Without treatment, this would be very undesirable, but if you’re looking to kill the parasite, heating your water simply encourages the parasite into its more vulnerable state so it can be killed much faster.

The only treatment for ich we have found effective is Malachite Green & Formalin, which will kill the free-swimming parasites on contact. Water changes help increase treatment effectiveness and also reduce parasite numbers, so are highly recommended. External antibacterial medicines can also be supplemented to prevent secondary infections occurring from open sores after the parasite has left the scales.

Treatment options include:

  1. Malachite Green & Formalin (Kills Parasite)
  2. Melafix (Secondary Infections)
  3. Water Changes (Parasite Reduction)
  4. Heating Pond Water (Speeds Treatment Process)

For more information, please refer to our Main Ich Guide here.

2) Koi Pox (Waxy, smooth, white spots)

how to treat koi pox
Carp pox white spots commonly appear on the tail and fins, being waxy and smooth in appearance.

Unlike ich, which is caused by an external parasite, carp pox is an inherited gene which causes periodic outbreaks of the herpes virus Cyprinid Herpesvirus 1, or “CyHV-1”.

The herpes gene will be present in carriers from birth, and it’s impossible to know if your fish have the gene until they begin showing signs of pox. Although pox is highly contagious between fish, it will initially lay dormant in carriers until periods of weakness or stress cause the virus to “wake up” and become active. During these periods the virus will begin to spread throughout the fish, and your koi will likely begin to display classic pox symptoms, such as white waxy spots across the body, fins, and tail. The waxy and glossy appearance of the white spots is the easiest way to identify if your fish has carp pox or another potential white spot disease.

Carp pox is very common within the koi hobby, and you’d be surprised how many of your fish may be carriers of the herpes gene without you even knowing it. Luckily, carp pox caused by the CyHV-1 herpes virus is not dangerous, and symptoms will eventually resolve as immune activity increases and the causes of stress are resolved. In fact, the more outbreaks of carp pox your koi get within their life, the less severe it becomes over time. This is because a koi’s immune system will slowly become accustomed to the virus, which means it can act much more rapidly in future when outbreaks occur. This is also why pox is much more common in young, weak, and immune-compromised fish in comparison to healthy, adult carp. Fish with pox should be handled extremely carefully, as the virus will spread throughout the pond if spots are broken.

Koi Pox Symptoms:

  • Waxy, smooth white spots (commonly on fins & tail)
  • No interest in feeding
  • Hiding away & swimming slowly
  • Loss of color & duller appearance
  • Bacterial infections (if spots are broken)

How to Manage & Treat Koi Pox Symptoms 

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Sadly, there is no cure for carp pox, so treatment involves management of symptoms, reducing causes of stress, and improving immune activity. Unlike bacterial and parasitic infections, viruses are much tougher to eradicate due to how they reproduce within healthy host cells. Any treatment to destroy the virus would effectively destroy the healthy host cells, which in turn, would eventually kill the fish. However, fish with pox are not completely vulnerable, and over time their immune system will become very effective at destroying new viruses before they can spread. Since their immune system is the first and last line of defense in treating pox disease, taking steps to improve their immune activity, health, and comfort will all help reduce pox outbreaks and symptoms.

As carp pox tends to flare up during periods of low immune activity, such as winter torpor, steps should be taken to ensure koi have the best chance during these periods. For example, treating for parasites is common practice before winter, as they tend to infect fish when their immune systems are at their weakest in cold weather. Parasite infections will also lead to stress, and stress will lead to carp pox outbreaks – and both together are a bad combination! Likewise, feeding your fish a high quality feed with immune boosting properties can help strength their immune system, and heating the pond can also keep pox at bay as immune activity is higher in warmer temperatures. Keeping water quality in good order, and performing regular water changes are also vitally important to preventing infections, illness, and lowering stress.

Treatment options include:

  1. Winterization (Safe Hibernation)
  2. Aqua Prazi (Parasite Prevention)
  3. Water Changes & Good Water Quality
  4. High Quality Koi Foods (Healthier Fish)
  5. Heating Pond Water (Increased Immune Activity)

For more information, please refer to our Main Pox Guide here.

3) Koi Ulcers (White spots with red borders)

what causes ulcers in koi fish
Ulcers are caused by bacterial infections, leading to a white spot or open wound with reddening borders.

Regardless of how well we maintain and clean our ponds, there will always be some level of bacteria present, and not all kinds are beneficial. Unlike the aerobic bacteria contained within our filter media which helps break down harmful waste substances, there are other kinds of natural bacteria in ponds that can lead to sickness, disease, and ulceration. In most cases, the levels of harmful bacterium never rise to a point where they can cause issues with koi, but if the pond is in particularly bad condition, or fish are already sick, even a small amount of bacteria can be dangerous.

In terms of ulcers, two naturally occurring bacteria which thrive in poor water quality, the aeromonas and pseudomonas bacteria strains, are the most common types responsible for the formation of painful ulcers. These two strains can be found in most bodies of fresh water, but don’t often cause issues as carp have natural slime coats to protect them from outward infection. If their slime coats are compromised, however, due to sickness, poor conditions, or malnutrition, the bacteria can penetrate and cause infections.

The white spots which display with ulcers are unique among other white spot diseases, as instead of leading to a possible bacteria infection, the white spot will indicate an infection is already present. This is usually displayed as a redness or rash that surrounds the spot, with the center being filled with infectious bacteria and mucus. Without treatment, or if the koi is handled poorly, the ulcer can rupture which will lead to an open wound and possible infection between fish. Ulcers tend to form after an injury, parasite infection, or preceding illness that leaves the koi with open sores which then contract the free-swimming bacteria.

Koi Ulcer Symptoms:

  • Injury or sore that doesn’t heal
  • White spot with reddening borders
  • Lack of feeding interest
  • Dull coloration & appearance
  • Strange swimming behaviour
  • Parasite infections, especially flukes

How to Manage & Treat Koi Ulcer Symptoms 

Ulcers are caused by bacterial infections, so can be treated very effectively with antibiotic medicines. Although in the early stages they respond well to external treatments, it’s often best to still treat with antibiotics to prevent the chance of internal infections occurring. In our experience, Kanamycin is one of the more effective antibiotics for treating ulcers, and should be mixed in with fish food for maximum absorption. Kanamycin can be found in KanaPlex (containing 35% kanamycin) , but you would also need to make use of a binding agent to combine it with food, such as Seachem Focus. Although you CAN treat the pond itself with antibiotics, this is NOT recommended, as it can have a hugely negative effect on the ecosystem and cause more issues later down the road.

If the ulcers were caused by parasites, the pond should be treated with a wide-spectrum parasite killer, such as praziquantel, and an external antibacterial treatment can be useful for recovery. Since the two main causes of ulceration are the aeromonas and pseudomonas bacteria strains, KoiZyme can be used to reduce them over time. This treatment adds new bacteria to the pond which is safe for fish, and this new bacteria competes with the harmful strains, eventually starving them of nutrients. Alongside treatments, ulcers can be prevented by maintaining good water quality, healthy fish, and a strict cleaning and water change routine.

Treatment options include:

  1. KanaPlex & Seachem Focus (Treats Infection)
  2. AquaPrazi (Parasite Control)
  3. Melafix (Improves Recovery)
  4. KoiZyme (Harmful Bacteria Control)
  5. Water Changes & Good Water Quality

For more information, please refer to our Main Ulcer Guide here.

4) Koi Lymphocystis (White cauliflower-shaped lumps)

a fish with lymphocystis
Sea bream with B) mild lymphocystis and C) severe lymphocystis. Photo by Arik Diamont,

Lymphocystis, in our experience, is the rarest white spot disease here, but also one of the most easily distinguishable in later stages. Although many experts can go decades without seeing a single case in cyprinids like goldfish and koi, going so far as to say that it cannot impact this group of fishes is inaccurate.

In 2018, several juvenile goldfish kept in an aquarium were observed to have milky white lesions on their skin, which extensive laboratory testing confirmed to be lymphocystis. In India from 2017 to 2019, there was an outbreak of lymphocystis in adult farmed grass carp. As goldfish, grass carp, and koi are all cyprinids, it is quite reasonable to assert that, though rare, what is able to infect one species within this group can also infect others, i.e.: koi.

Similar to pox, lymphocystis is caused by a virus, this time of the genus Lymphocystivirus within the Iridoviridae family. It’s not exactly known what causes the virus to occur, however, similarly to pox, some believe that an inherited gene is responsible and outbreaks occur during times of stress, illness, or low immune activity.

In the early stages, the disease is visually similar to the white spots of ich, and can easily be confused with the parasite at this stage. Since it’s difficult to know for certain until the virus develops further, carrying out an ich treatment protocol is good practice just in case symptoms overlap. If fish do not respond to ich treatment, or the virus is allowed to develop in time, the small white spots will eventually begin to grow and clump together, leading to cauliflower-shaped growths. The disease tends to appear differently for certain species, and is most common on the fins and tail of koi, but can also appear on the body, head, and gills. Since the immune system is responsible for management of the virus, the disease commonly forms in areas with less exposure to the immune system, such as in tissues with a thick hyaline membranes. This allows the virus to essentially “hide” from the immune system in the early stages, and it’s not until the virus begins spreading to other parts that you will see an immune response.

Although the large white growths are unsightly, especially in ornamental koi, they’re not usually dangerous and require no additional treatment. As the fish’s immune system begins to recognize the virus, it will gradually bring the symptoms under control within a 2-4 weeks period. However, if water conditions are poor, or fish are already sick or unhealthy, complications can occur from secondary infections and the spreading of lumps to gill tissue (respiratory problems), mouths (feeding trouble), and eye sockets.

Koi Lymphocystis Symptoms:

  • Small white spots, commonly on fins/tail (early stages)
  • White clumps resembling cauliflower (later stages)
  • Unusual swimming behaviour
  • Loss of buoyancy
  • Lack of appetite
  • Dull scale color & pattern

How to Manage & Treat Koi Lymphocystis Symptoms 

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As with the pox virus, there is no cure for the virus that causes lymphocystis, and primary treatment involves the management of symptoms and good husbandry. Since the first and last line of defence against lymphocystis is the fish’s immune system, ensuring fish are comfortable and healthy within their environment can help control outbreaks and speed up the healing process.

Feeding a high quality fish food with immune boosting properties can be beneficial for maintaining a strong immune response, and keeping water quality in-check will help reduce possible environmental stress. Regular water changes are useful for removing excess waste, and will also help reduce any possible free-swimming parasites and harmful bacteria that can cause secondary complications. Providing plenty of aeration throughout the year, and carrying out an effective “winterization” routine can also help with prevention and recovery.  Finally, since immune activity is increased in warmer temperatures, heating your pond water or quarantine tank can speed up the response of the immune system and greatly reduce recovery time.

If the virus is allowed to spread to gill tissue, the mouth, or the eye sockets, the lumps may need to be removed by a professional veterinarian. After lumps have been removed, an antibiotic bath will likely be prescribed to help prevent any external bacterial infections occurring during the healing process.

In most cases, there is very little you can do for lymphocystis apart from let the disease run its course. So long as water conditions are good, koi are healthy, and fish are comfortable, symptoms will eventually reside as the immune system gains control of viral activity.

1 thought on “How to Treat Koi White Spot Diseases (Causes & Treatments)”

  1. My koi has ..what looks like are two ,hard looking bubbles on its tail fin…What do you suggest for treatment? Sylvia Procter


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