How to Treat Dropsy in Koi Carp (Safe Treatment Guide)

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Guide to Koi Dropsy Treatment & How to Prevent it Coming Back (updated)

what causes dropsy in koi
Dropsy is caused by a build up of fluids within a koi’s body, causing swimming problems and swelling. Public domain.

The word “dropsy” is an old fashioned term which refers to the swelling that occurs throughout the body due to fluid retention, and is interchangeable with the more modern term “edema.” Even though it’s no longer used in human medicine, dropsy has retained popular usage within the fish keeping hobby to refer specifically to fluid swelling in fish. It is also sometimes called “dropsy disease”, or “pine-cone disease,” due to some of the symptoms that present in advanced stages.

Although the name has a humorous ring to it, it’s anything but funny, and can often be fatal in advanced cases. Dropsy in koi is usually caused by internal infections, leading to bodily swelling caused by the failure of organs, commonly the kidneys. Early symptoms include a slight bloated appearance, loss of buoyancy, lack of interest in feeding, and a tendency to hide (shyness). It’s important to treat your koi as a precaution if you notice similar symptoms, as the cause is usually curable in the early stages with a combination of anti-parasitical, anti-bacterial, or anti-biotic medications.

In more advanced stages of the condition, the koi will have major swelling to the body, causing the eyes to bulge and the scales to stand up with a pine-cone appearance  (hence, “pine cone disease”). At this stage of the infection, it’s often fatal as liver damage is common, but steps can still be taken to try to alleviate stress, reduce symptoms, and encourage recovery.

Dropsy Koi Symptoms:

  • Swelling or “bloated” bodily appearance
  • Swollen eyes and sockets (Advanced stage)
  • Scales which look like pine cones (Advanced stage)
  • Loss of swimming buoyancy
  • Duller color & pattern
  • Hiding and extreme shyness (Stress)

As dropsy is so difficult to cure in later stages, the best treatment is always prevention! Steps should be taken to improve water quality, fish health, and pond conditions if your fish are showing warning signs of infection (more details on this below).

What Causes Dropsy Disease in Koi?

skin fluke under a microscope
Parasites, such as flukes (pictured) can cause dropsy to occur in fish. Source: The Scottish Government – Gyrodactylus Salaris Working Group (GSWG)(Archive)

Dropsy is usually caused by an underlying infection which leads to damage to organs and tissue causing fluid retention. The single most common cause of dropsy is poor water quality, leading to fish becoming stressed, sick, and prone to infection. Parasites, such as flukes, can lead to open wounds and be a breeding ground for bacteria, leading to bacterial infections. Injuries left untreated in poor water conditions will heal slower, and there is a much greater chance of internal infection occurring. Even though poor water quality may not be directly causing the problem, the poor conditions often act as a catalyst for infections and illness to spread and worsen.

As well as poor water quality, lack of proper nutrition from feeding can cause issues; once again, making fish more prone to illness and infections. Feeding koi with a highly nutritious food with high proteins, fats, vitamins, and minerals will ensure they have a strong immune system and are in good health to fight back any illness. Properly wintering your koi pond is also important, as this is when koi are most vulnerable to infection from bacteria and parasites.

Injury is another cause, which can be attributed to predators, such as herons, cats, or raccoons. Predators and pests may also bring with them nasty parasites and bacteria from other ponds, leading to your own fish becoming sick and spreading illness. New plants and fish should be quarantined for this very reason, as new arrivals can also bring with them disease, bacteria, and parasites which can infect your current fish stock

Causes of Dropsy in Koi & Goldfish:

  • Poor Water Quality
  • Parasitic, Viral, or Bacterial Infections
  • Lack of Nutrition (Poor Quality Feeds)
  • Kidney Damage (Drug/Medicine Usage)
  • Stress or Injury

Is Dropsy in Koi Contagious? Should You Quarantine?

Stock tanks are useful for quarantining fish, and although dropsy isn’t usually contagious, they can help with treatment.

Although most cases of dropsy aren’t contagious, it’s still good practice to quarantine sick fish just as a precaution and to make treatment easier to manage. Bacterial infections due to injury aren’t usually contagious, however, parasitical infections and infections by some rare bacteria (mycobacterium tuberculosis) are highly contagious and can spread to other fish. Since the symptoms can be very similar between dropsy cases, quarantine is recommended to be on the safe side!

Goldfish can be easily quarantined in a large aquarium, but koi carp will require a much larger holding tank as most medicine will need to be diluted in a certain amount of water to prevent overdose. Stock tanks, often used by breeders and show koi, are great for this purpose, providing a temporary holding environment to treat sick fish with plenty of wiggle room. Moving koi over to a stock tank will ensure treatment is dosed more accurately and your other koi are not in danger of contracting the same illness or side effects of medicine.

Another advantage of having a dedicated quarantine tank is you’re able to quarantine new fish and plants before placing them in your main system. All new arrivals should be quarantined for 3-4 weeks, as this is the average incubation period of many common parasites. You can even choose to treat new arrivals with anti-bacterial and anti-fungal treatment as a precaution, as many products are safe for fish and should not cause unnecessary stress.

Dropsy Koi Treatments & Prevention Methods

Note:  Always read dosage instructions before treatment, and make sure to turn off any UV clarifiers and remove any active carbon as it will neutralize medications. 

Treatment for dropsy will depend on the underlying cause; whether the infection is bacterial, fungal, or parasitic in nature. The problem with dropsy is that it’s difficult to tell, as all cases show very similar symptoms. Due to this, treating fish with a wide-range treatment, both anti-bacterial and anti-parasitic, is often best to ensure all causes are covered. Below are some possible treatment paths:

1) Anti-Parasite Treatment

aqua prazi fluke and parasite treatment for koi dropsy
Aqua Meds Aqua Prazi Fluke and Parasite Treatment.

For parasite treatments, we recommend praziquantel, as it acts as a broad-spectrum parasite killer, being particularly effective against flukes and tapeworms. This treatment will be able to kill both external and internal parasites, and can be dosed alongside an anti-bacterial medicine for prevention against infection. Although it can be used on just the sick fish in quarantine, treating the entire pond can be beneficial as parasites are highly contractible between fish. Aqua Pazi (praziquantel) treatment is safe for pond usage and should have no ill effects on water quality or the eco-system if dosed correctly.

2) External Anti-Bacteria Treatment

If the cause is external injury, anti-bacteria medicine, such as Melafix, can help with direct healing and treating external infections. However, external treatments are often less effective against cases of dropsy as the problem usually spreads internally to other organs (when signs of dropsy show). Treatments like Melafix are helpful for healing wounds, but if there are also signs of dropsy,  you may need to try a broad-spectrum antibiotic medicine, such as kanamycin, to fight back internal infection (see below).

3) Internal Anti-biotic Treatment (Advanced Stage Dropsy)

antibiotic medicine for fish
Kanaplex Antibiotic Medicine.

KanaPlex (35% kanamycin) is a good choice of antibiotic, but as it’s intended for aquariums we recommend mixing with koi food using a binding agent, such as Seachem Focus. This will prevent the need to purchase large quantities of antibiotics to cover the water volume, and ensure 100% of the medication is being absorbed by the fish and does not interfere with pond balance.

1 scoop of KanaPlex is mixed with 1 scoop of Focus, and this is added to a table spoon of food (pellets) and a few drops of water for easier absorption – once a day. After a week of daily feeding you can evaluate the results, and if there is no improvement, you can repeat the dosing for an additional week. Other antibiotics, such as minocycline (maracyn), can also be used, but they may not be as effective against dropsy as they cannot be bound to food.

Unlike other treatments, antibiotics CAN have a negative impact on your pond’s ecosystem, as well as causing an increase in drug-resistant bacteria. Always treat fish with antibiotics in a separate quarantine tank, as this is safer for the pond and more comfortable for the koi.

Methods for Preventing Dropsy Disease in Koi & Goldfish Ponds

1) Deter Predators & Stop Pests

herons koi dropsy bacteria
Predators, such as herons, can be carriers of foreign bacteria and parasites. Public domain.

A leading cause of dropsy is bacterial infections caused by parasites that leave nasty open wounds and sores on the fish. If you’re only now finding parasites in your pond, and have not had problems before, they’re likely being brought to the system by a foreign body. Common culprits include predators and pests, such as herons, cats, raccoons, and even ducks! All will be moving between different ponds, and they could be bringing all the bacteria and parasites with them. Predators will not only bring parasites, but will also cause injury to your koi and can leave them with wounds which increase the chances of infections occurring. Ducks, although not hunters, are very messy and their faeces will cause all sorts of issues in your pond with water quality, while also bringing along an equal number of bacteria and parasites. Both predators and pests should be deterred to ensure good water quality is maintained, fish are safe, and parasites/bacteria can’t invade.

  • For our full predator protection guide, check here.
  • For our guide on stopping ducks arriving, see our article here.

2) Quarantine New Fish & Plants

As well as predators and pests, new fish or plants can also bring along harmful bacteria, parasites, and diseases which can quickly infect your main pond system. If you’re adding new fish or plants to your pond you should always quarantine them in a separate stock tank for 3-4 weeks before adding them with your other fish. The average egg incubation period of many parasites is 4 weeks, so during quarantine you can you monitor the fish closely and check for any adults or larvae hatching. If the fish is sick, or has a growing infection, it will also start showing during this period, which means you can avoid it spreading to your main pond by treating them separately.

Many fish keepers choose to treat new arrivals with an anti-bacterial and anti-parasite medicine just as a precaution, as many are safe for fish when dosed properly. We recommend Melafix for external bacteria and Aqua Prazi for parasites. Unless your new fish are showing signs of an internal infection, antibiotics are rarely needed during quarantine and should always be used sparingly as they can cause bacteria to become resistant to the medicine over time.

3) Improve Water Quality

Parasites, bacteria, and fungi all thrive in stagnant, dirty, and low quality water conditions. It’s important to optimize water quality for your koi to minimize the risk of infection, and to keep them comfortable and stress free. Water quality should be tested throughout the year, with good times being Spring and Autumn, and any problems with quality resolved before they can worsen. Water filtration needs to be cleaned and optimized, and beneficial bacteria should have plenty of oxygen to break down waste efficiently. Filter media needs to be cleaned properly, and you can further optimize it with activated carbon treatments or better quality media. For more information of maintaining good water quality, see our articles below:

4) Feed Nutritious Koi Food

You’d be surprised how low quality many commercial koi feeds actually are, and how little real nutritional value they provide your koi. Although it may sound less important than other things, feeding your koi a highly nutritious feed with all the essential ingredients should be towards the top of every koi keepers list! A quality feed will help make your fish stronger (to fight illness), improve their immune systems (to prevent illness), and reduce waste they produce (which improves water quality).

Your koi feed should be high in an aquatic sourced protein, such as fish meal, and this needs to be the 1st ingredient on the label so you know it’s the highest material by weight. Second, you’ll want a good percentage of healthy fats (4-10%), and a wide vitamin and mineral profile for general health and immune support. Not only will your koi be healthier with a higher quality feed, they’ll enjoy feeding more which can help you create a stronger bound with your fish so you can more easily spot problems in future. For more information on our top koi food choices, check our guides below:

5) Get Ready for Winter!

Koi carp enter a state of torpor (commonly mistakenly referred to as “hibernation”) during winter, meaning most of their bodily functions slow down to a crawl, but not as deeply as in true hibernation. During this period they’ll stop taking food and need to live off their summer fat stores, and their immune system will be almost completely shut down. For these reasons, koi are the most vulnerable to both bacterial and parasitical infections during their hibernation period, so steps should be taken every year to protect against this – a process called “winterization.”

Wintering your pond includes a big clean-up in Autumn, adding heating equipment for gas exchange, feeding high quality food in summer, and dosing with anti-parasite treatment before topor kicks-in. Cases of dropsy koi are common in Spring, as the fish easily become infected during winter when their immune systems are slower. Taking steps to remedy this is important for preventing dropsy and ensuring fish are stronger come Spring and the New Year. For the complete A-Z guide on effective winterization in fish ponds, see our dedicated article below:

1 thought on “How to Treat Dropsy in Koi Carp (Safe Treatment Guide)”

  1. This is EXCELLENT information. I recently bought a house and the owner has abandoned roughly 12 Koi carp of different sizes, One seems to be quite ‘fat’.. I have no idea about pond cleaning, or winterization.. or stopping feeding them, Until now.
    I think best foot forward is to call a Vet for some direct advice,

    Thankyou to all contributors.


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