Brooklynella Clownfish Disease – Causes & Treatments

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Clownfish aren’t known to be extremely sensitive to diseases and parasites which is obvious if you assess the fish’s lifespan. These fish can live up to 30 years in the wild, so they must be doing something right.

This being said, there is a specific health problem that can turn ugly fast. We’re talking about Brooklynella disease, which is mostly known as the clownfish disease. This condition can depopulate an entire tank and won’t limit its spread to clownfish only. Immediate diagnosis and treatment are vital to save the hosts’ lives and contain the spread.

But let’s discuss this condition more in-depth for a clearer picture.

What is Brooklynella Disease?

This condition is the result of the infestation with a smooth, fast-swimming, and deadly protozoan called Brooklynella hostilis. The name is a dead giveaway of the organism’s deadly nature. This microorganism looks like a small bean covered in fast-moving cilia designed to propel the creature that’s always looking for viable hosts. This parasite cannot survive without a host, so it needs to find one fast.

The method of infection is virtually unavoidable, as the protozoan will attach to the host’s skin and move around, looking for a way in. The most widespread method of infection is via the gills, but it can also enter the body via microtears in the skin.

Once the parasite reaches the gills, though, your clownfish will begin a race against time. Brooklynella is fast-acting and deadly, so your fish may only have several hours left to live.

Is Brooklynella Disease Contagious?

Yes, it is. Brooklynella is highly contagious, and it can infest the entire clownfish tank in a matter of hours. Fortunately, the infected fish will showcase immediate signs of discomfort, allowing you to detect the problem in time. So long as you pay attention, of course.

The symptoms may vary, depending on the point and severity of infection, but they follow the same general outline.

What are the Symptoms of Brooklynella?

Fortunately, the clownfish will showcase a variety of symptoms, most of which are immediate following the infection. I use ‘fortunately’ here not in an ironical but rather a pragmatical manner. That’s because the immediate and clear symptoms will allow you to identify the problem sooner.

Some of the key symptoms relating to Brooklynella include:

  • Behavioral changes – The fish will begin to rub against various hard surfaces in the tank due to the parasite’s activity at the skin level. Skin lesions may appear because of it, which are predisposed to bacterial infections. The fish will also appear lethargic and will refuse to eat.
  • Signs of suffocation – These occur when the parasite has already reached the gills, rendering the fish unable to breathe properly. Your clownfish will rapidly open and close its mouth, swim to the water surface to breathe, and display rapid gill movement. Asphyxiation is the most common cause of death in these cases.
  • Physical symptoms – We’ve already mentioned skin lesions, but affected fish also display a variety of other symptoms. Skin discoloration is another sign, along with excessive mucus production. The latter signifies the body’s attempt to protect itself from the parasite. Other notable signs include skin redness around the infected area and even fin rot resulting from secondary infections of bacterial origin.

Given that behavioral changes come first in line, you should quarantine the fish at the first sign of trouble.

What Causes Brooklynella Disease?

There are 3 potential sources for Brooklynella:

  1. Infected fish – Simply put, you’re buying already sick fish that don’t immediately showcase any visible symptoms. And even if they do, you tend to wave them off as being specific to the acclimation process. The sick fish will immediately infect the healthy ones already present in the tank with devastating consequences.
  2. Infected water – The water you’re using for your fish tank can make the difference between life and death. Avoid rainwater and tap water or, at least, boil them before use. Tap water also requires dichlorination due to the often excessive chlorine content. I recommend RO/DI water types, along with a good water conditioner for remineralization, just to be sure.
  3. Infected decorations and plants – This infection path is less common, but we have to mention it because it’s still possible. Rocks, driftwood, and even plants can contain a variety of hitchhiking micro and macroorganisms that could infect the tank. The Brooklynella parasite is one of them, but we also include algae, snails and snail eggs, worms, and other bacteria and parasites.

The solution? Always quarantine new-coming fish for at least 2 weeks before adding them to the main tank. This will eliminate the risk of your fish carrying any dangerous pathogen into the main population. When it comes to decorations and plants, always disinfect them thoroughly before use.

For this purpose, you can use bleach, vinegar, or hydrogen peroxide, among other solutions.

How to Treat Brooklynella Disease?

Once you’ve identified the condition, you need to begin the treatment asap. This deadly and highly contagious disease will kill your fish quickly. Here are the necessary steps to follow:

  • Quarantine – Make no mistake, quarantine is an essential step in the treatment process. You should remove all sick fish from the environment, which is most likely all fish. Quarantine is necessary even if all the fish are infected. The goal is to remove the fish from a pathogen-infested environment which can make the treatment more difficult.
  • Formalin treatment – Formalin is a solution comprising formaldehyde gas and methanol mixed with water. Aim for a formaldehyde concentration of 37%. Mix the solution with water in a separate container and dip the fish briefly into the mix. The critical thing to know is that the solution is extremely powerful, so you shouldn’t keep your fish into it more than 1 or 2 seconds. Always follow the instructions to the letter and contact a vet if you’re unsure how to go about it.
  • Maintenance – The formalin bath will eliminate all of the skin parasites and clear the gills of mucus. This will immediately improve the fish’s respiration and set the stage for gradual but sure recovery. You can now move the fish back into the quarantine tank and begin the maintenance process. The fish will remain quarantined at least 2 weeks, during which you will perform daily water changes (15%-25%) and regular tank cleaning. A nutritious and balanced diet is necessary to keep the fish’s body in peak condition during recovery.

My personal advice would be to contact a vet before starting the treatment. I understand that time is not your friend under these circumstances, but it’s better to lose 15-20 minutes figuring out the best treatment layout and approach than have the treatment procedure kill the fish. Remember, the difference between medication and poison is in the dose, which is even more true with formalin.

Your fish should show signs of recovery within 1-2 days if the treatment is successful. Even so, keep it in quarantine for at least 2 weeks to make sure everything’s fine. If the clownfish doesn’t show any sign of recovery, the damages may be too extensive, in which case euthanasia may be the better option.

Will Brooklynella Kill Your Clownfish?

Yes, Brooklynella will undoubtedly kill your clownfish. This is an extremely aggressive pathogen with an obscene death toll in the clownfish population. Immediate diagnosis and treatment are vital to save your clownfish’ lives.

Needless to say, prevention is key when discussing Brooklynella. Here are the 2 primary prevention tips to consider:

  • Source your clownfish wisely – Avoid commercial fish shops. These places are notorious for mistreating clownfish and keeping them overcrowded in improper aquatic conditions. They also don’t care much about balancing the fish’s diet accordingly. This results in weak clownfish with poor immune systems, living in parasite and bacteria-infested waters.
  • Quarantine new fish – The quarantine period is 2 weeks or more, so I understand why most aquarists tend to skip it. But, by doing so, you’re not doing your fish any favors, on the contrary. Give the fish some time, place it in a safe and clean quarantine tank, and observe it for a couple of weeks. This timeframe is sufficient to identify any potential health problem your fish might face.

Plus, always sterilize any new plants or decorations you plan to add to the tank. I’ve already written extensive guides on the topic you may want to consult.


Brooklynella disease is deadly and contagious and can depopulate your tank fast. While there are no definitive ways to prevent the condition with 100% effectiveness, you can take action to reduce its impact.

Follow my recommendations, always monitor your fish, and quarantine them at the first sign of trouble.

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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