Clownfish disease (Brooklynella hostilis)

Let’s take a closer look at brooklynella, also known as the clownfish disease. Brooklynella is a marine fish parasite which belongs to the class of ciliates.


Common symptoms observed in fish infected with brooklynella hostilis are:

  • Rubbing and flicking
  • Changes in color of the skin to bad condition
  • Thickening of the slime coat
  • Development of opaque to whitish patches that eventually detach
  • Cloudy eyes
  • Rapid, heavy breathing
  • Frayed fins clamped to the body

If you observe these symptoms, you should start treating your fish appropriately. We recommend eSHa OODINEX in reef tanks or eSHa TRIMARIN in fish-only tanks.


Let’s dive deeper into ciliates. Ciliates are a group of microorganisms with hair-like cilia on the outside. These cilia can move back and forward and can be used for locomotion. The entire single celled body of brooklynella is covered with a layer of cilia. Brooklynella is bean-shaped and somewhat resembles the freshwater parasite chilodonella. An outbreak of brooklynella leads to a change in color of the fish with the bright colors fading over time.

Due to the irritation caused by the parasite the fish can start rubbing their body or head and eventually a thick layer of mucus develops. This thickening of the slime coat makes the body of the fish appear whitish with accumulations of mucus. The beginning stages are visible when looking at the fish head on and when focusing on the fish turning sides in the water. You can see the mucus build-up on the skin and also the frayed fins that are usually clamped to the body.

Another clear symptom is the cornea of the eyes turning cloudy. Brooklynella not only affects the skin, but also the gills of fish, causing asphyxia and suffocation, with heavy rapid breathing as a clear symptom. In later stages patches of mucus begins to detach from the body, like skin flakes falling off, and secondary bacterial infections develop. If the outbreak of parasites is not stopped in time, it could ultimately lead to the death of these fish in the aquarium.


Luckily it can be treated! eSHa OODINEX is specially designed for use in reef aquariums, which are inhabited not only by fish, but also invertebrates such as anemones, corals, shrimps, an others. Be aware though, OODINEX should not be used with poisonous urchins, poisonous planaria or other poisonous animals. We recommend to quarantine newly acquired marine fish in a separate quarantine tank using OODINEX or TRIMARIN to protect your fish from protozoan microorganisms.

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