Goldfish Lymphocystis – Causes & Treatments

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Despite being naturally resilient to environmental changes and regular fish disorders, goldfish may sometimes fall prey to rarer conditions that are difficult to treat safely.

These are especially problematic precisely because they aren’t that common, causing confusion among novice goldfish keepers who have never faced anything similar.

Such is the case of lymphocystis, a viral disease that can cause a multitude of symptoms and is notoriously difficult to treat.

But what is this condition, how does it manifest, and is there a way to treat it? Let’s find out!

What is Lymphocystis?

Lymphocystis is a viral disease caused by the Lymphocystivirus, a pathogen that infects the host’s tissue, grows and multiplies fast, and pops out, spreading throughout the environment in search of another host.

To better understand what you’re dealing with, here is some key information to write down:

  • The pathogens form body nodules – These are known as fibroblasts and represent infected cells housing thousands of viral pathogens, multiplying relentlessly. The fibroblasts are connected to the fish’s healthy tissue, drawing in nutrients and supporting the pathogen’s life cycle. Upon maturity, the fibroblasts will burst, releasing the virus into the environment to look for other hosts to infect.
  • Small beginnings – The body cysts will be very small and seemingly innocuous at first, resembling Ich due to their white and yellow coloring. This makes proper diagnosis more difficult, allowing the virus to develop and multiply as a result.
  • Low death rates – The lymphocystivirus is one of the 3 genera of viral pathogens belonging to the Iridoviridae family. The other 2 are the Ranavirus and the Megalocytivirus, and these have higher mortality rates than the former. This makes the lymphocystivirus easier to treat, which doesn’t take away from its gross appearance.
  • Benign in nature – Lymphocystis isn’t really a dangerous condition since it doesn’t cause any severe long-term health problems. The only impediment is primarily esthetic since the fibroblasts can grow to impressive sizes, affecting the fish’s appearance. In some cases, they may also affect the fish’s ability to swim, move, and float, which tends to happen in more advanced phases. That being said, goldfish can die due to being infected with the lymphocystivirus, which is why early treatment is necessary to prevent health complications along the way.
  • Long incubation period – The long incubation period is this virus’s strongest point. Allowing it to remain undetected inside its host for several weeks or even months. This is a problem for several reasons. One of them is the fact that sick fish become latent carriers, displaying no sign of infection, which will postpone the necessary treatment that could stop the disorder. By the time the first symptoms emerge, the disorder is already advanced. The second problem is that the virus’s long incubation period often outweighs the quarantine timeframe that newly purchased fish need to go through. So, you might quarantine the fish to make sure they’re not sic. And introduce them into the tank several weeks later, along with the virus. As we will soon see, this is a major issue.

Now that you know how the disease functions, can you treat it? The answer is a bit trickier.

How to Treat Lymphocystis in Goldfish?

There is no reliable treatment method for lymphocystis. All you need to do to counter the disease is to rely on your fish’s own immune system.

The fish will eventually overcome the disorder in most cases, provided its immune system is strong enough to overcome the problem.

That being said, your goldfish requires certain conditions to fight off the infection effectively.

These include:

  • Quarantine – This is a viral infection, so protecting the rest of the goldfish population is key to preventing the pathogen’s spread. Even if you have no other fish, it’s still worth quarantining the sick specimen. It turns out that the lymphocystivirus can live up to a week in the tank’s water in search of a host. This amazing resilience is one of this pathogen’s keys to success, improving its chances of finding a viable host.
  • Balanced diet – Your goldfish will require a balanced and nutritious diet to strengthen its body and immune system. Provide your goldfish with a healthy and diverse meal plan throughout the quarantine phase. You could even supplement its meals with vitamins and minerals, provided your goldfish displays any type of deficiencies. Make sure you don’t overfeed the patient to prevent digestive problems and dangerous ammonia buildup in the tank’s water.
  • Optimal water parameters – Keep ammonia and nitrites to 0 and make sure the nitrate levels don’t go over 20 ppm. These parameters are essential for preventing the condition from worsening, especially since the goldfish is more sensitive during this time. Your treatment tank should have a heater and a filter to keep tank parameters as stable as possible during the quarantine phase. You also need to perform more frequent tank maintenance. Which includes water changes every 2-3 days and tank cleaning work to remove fish waste and food leftovers.
  • Stable temperature – As coldwater fish, goldfish usually prefer environmental temperatures around 68-74 F. I recommend increasing the tank’s temperature slightly during the treatment, preferably around 70-72. This will increase the fish’s metabolism and support its immune system during the treatment process. The higher temperatures will also speed up the pathogen’s life cycle, shortening the treatment’s duration.

You may also speak to your veterinarian, if you haven’t already, to discuss the option of using any medication to improve the treatment’s effectiveness.

Is Lymphocystis Contagious to Other Fish?

Yes, it is. The virus’s entire life cycle is based on spreading from one host to another. So if one fish is sick, others probably are too.

In this sense, here are some interesting facts about how the virus works:

  • Limited action – It appears that lymphocystivirus only infects around 140 fish species, both marine, and freshwater. The virus also shows host-specificity. Which is a specialized behavior, causing each new strain of the pathogen to only infect fish of the same species as the primary host. So, if your goldfish shows signs of lymphocystivirus, the resulting pathogen will most likely only infect other goldfish. This is good news if you keep your goldfish in a community tank with other fish species that may be impervious to the pathogen. But don’t take this information at its face value; you should still quarantine the sick fish, just to be sure.
  • The treatment may last for months – The treatment’s duration depends on your goldfish’s age, overall health status, the presence of any secondary infections, the quality of care during quarantine, etc. Depending on how your fish responds to the treatment, you should expect your goldfish to remain in quarantine between 2 weeks to 2 months. The good news is that you should be able to tell pretty soon if your fish will make it. If the fish’s condition doesn’t get any better within 2 weeks, you might need to consider euthanasia.
  • The surviving fish will develop immunity – Well, not really immunity, but rather a more robust immune system that now knows how to deal with the condition. The first outbreak will be the most severe, which is common for any viral epidemics, including those common in humans. The survivors will develop specialized antibodies that have learned how to deal with the pathogens and are ready for round 2, should it ever arrive. This means that any subsequent infections will be far less damaging by comparison.
  • Generalized quarantine – If you’ve detected signs of lymphocystis in your fish tank, you may need to quarantine everyone. Before doing so, however, I suggest diagnosing your fish accurately to make sure they’re infected before placing them in quarantine. After all, you don’t want to quarantine sick and healthy fish together. The problem is that visual inspection is generally insufficient in determining whether the fish is healthy or not. You should contact a professional for a microscopic test to detect minute fibroblasts if any present.

Unfortunately, if you have several goldfish in the same tank, one infected fish generally indicates that all of them are infected.

Some may begin to display the trademark nodules soon, while others may remain latent carriers for weeks or even months.

So, generalized treatment may be necessary for all fish, along with a thorough cleaning of the main environment to remove the pathogen from the water.

Is Lymphocystis Contagious to Humans?

Fortunately, no.


We’ve discussed about quarantining the goldfish to ensure adequate treatment. But how about addressing the free-floating virus in the main tank?

If any of your goldfish’s fibroblasts have leaked the pathogen in the water, the entire tank may need some quick disinfection.

The pathogen may remain in the tank for up to a week or more in search of a viable host. So, how can you remove it sooner?

There are 2 primary ways to do so:

  1. Use specific compounds – These include potassium permanganate (400 mg/gal), formalin (8000 mg/gal), or sodium hypochlorite (800 mg/gal). You should use these chemicals with caution, using gloves, protective goggles, and even a respirator to prevent inhalation. Keep the water temperature at 77 F for approximately 15 minutes while adding any of the compounds in the given quantities. This should be enough to eliminate all traces of the pathogen.
  2. Manipulate water parameters – The lymphocystivirus cannot live at high water temperatures or abnormally-high pH values. Boost your water’s pH to 11 or higher and increase the tank’s temperature to 122 F and above. Altering these parameters accordingly can eliminate the pathogen completely within 30 minutes.

You need to remove the goldfish from the tank before applying any of these treatments. And always measure water parameters before adding the fish back in.

This will probably last for a while anyway, since your fish will remain quarantined for quite a while.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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