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Old 03/09/2014, 06:51 AM   #1
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Join Date: Aug 2005
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Brooklynella hostilis and Uronema marinum

Brooklynella hostilis (Brook) and the less common, and often misidentified, Uronema marinum (Uronema) are both ciliate parasites similar to oodinium and Cryptocaryon irritans that infect the skin of many species of marine fish. Brook is often referred to as “clown fish disease” but while clown fish are highly susceptible, other fish can catch it as well. In recent years, Uronema has been commonly brought in with Chromis.

In both Brook and Uronema infections, acute symptoms can appear very rapidly and fish can go from being very healthy to near death in a few hours. Unless treated quickly, fish are more likely to die than to recover.

The life cycle of both parasites is similar to that of Velvet and Ich as described in other stickies. Both of these parasites have a direct life cycle: they live on the fish, feeding and the population growing very rapidly, then drop off into the water column (where they can live quite happily for some time) and then go on to infect another fish.

Symptoms and Diagnosis

Fish with either Brook or Uronema lose color very rapidly, appearing pale and “washed out”. Often there is thickening of the skin’s mucus; so much so that the fish appears to have a rough white coating . Fins may be frayed and the skin may evidence pealing. Often the scales are loosened in the infected area and may come away from the fish when it is caught in a net. The major difference between Brook and Uronema is that the lesions associated with Uronema marinum have a more defined margin between the thickened mucus and normal skin that is often red and inflamed. However, the symptoms and treatments are so similar that accurate diagnosis is not required for successful treatment.

Behavior of the fish toward the end of life includes rapid breathing, no feeding and the fish becomes listless, hanging near the surface or sitting on the bottom of the aquarium. If the fish are examined carefully during the end stages they often look thin and the skin appears to be stretched tightly over the muscle blocks. This is because the fish has lost water through the lesions caused by the parasite as it feeds on the skin, and the animals have become acutely dehydrated.
It is quite difficult to misdiagnose these infections; the most frequent disease that it can be mistaken for is marine velvet (Amyloodinium ocellatum). However, fish with marine velvet do not develop such a severe mucus layer nor do the fins become brittle. Also marine velvet tends to be a sort of pale gold color unlike the white lesions of Brook and Uronema.

1. Do not share equipment between tanks (good practice in any case)
2. Quarantine your fish AND invertebrates

Quarantine your fish AND invertebrates
Foregoing quarantine is the most common way that parasites get into a system. Fish with a low level of infection or water from an invertebrate system that has infected fish in it are the major sources of bringing this parasite into a reef tank. Quarantine period is critical. It has been calculated with a 50% safety value that to be 95% certain that any fish is marine white spot free then the quarantine period should be 71 days (just over 10 weeks), for 99% certainty increase the period to 84 days. Quarantine period and fallow requirements are described in more detail in one of the stickies in this group of marine fish disease descriptions. However, a confidence interval of 90% is achieved at 6 weeks and for many reef keepers 6 weeks plus a prophylactic treatment is considered a gold standard. Why quarantine my invertebrates? Well you can introduce trophonts, theronts or tomonts either with the water or on living rock or a coral’s skeleton. As such anything that is wet should ideally be quarantined, most especially if it came from any system containing fish.

Environmental Treatments
Freshwater dip

In freshwater the parasite drops off the skin of the fish very rapidly. However, not all parasites drop off so while this improves the situation it does not correct it completely. If the fish are simply returned to the tank where the outbreak occurred then they will just become re-infected. For this treatment to be effective the fish should be kept in a quarantine tank and the main display tank kept fish free for 8 to 12 weeks. Once in the quarantine tank the treatment should be repeated on days 1, 2, 3, 5, 7 & 11 followed by 4 to 6 weeks of observation in a quarantine tank.

As these parasites breach the skin as they feed on the fish the skins integument is broken and the fish’s osmoregulatory potential is hugely reduced. This is exacerbated in freshwater so remember that a heavily infected fish could easily become physiologically stressed with this treatment method, ironically due to dehydration!

One of the most important things about a freshwater dip is that it will buy you some time to start another treatment or to set up a quarantine tank as even a very badly infected fish can lose most although not all, of its parasite in a few minutes and improve quite dramatically.

To carry out a freshwater dip:
1. Take some freshwater (RO is best) and heat it up to the same temperature as the tank
2. Adjust the pH of the freshwater to match the tank using a commercial pH buffer.
3. Catch the fish and pop it into the freshwater bath, watch the fish carefully and be prepared to remove it if it becomes very distressed. Normally 3 minutes in a freshwater bath will dislodge most parasites; this can be extended to five minutes.
4. Catch the fish and put it back into the tank. Do not pour the freshwater back in the tank as this may introduce the parasites back into the display tank.

Chemical Treatments - Formalin

While formalin is toxic, carcinogenic and an irritant, it is, however, one of the best treatments for Brooklynella hostilis and Uronema marinum. It can be purchased readily from your chemist and some off-the-shelf cures contain it or a related chemical (paraformaldehyde or gluteraldehyde) so a read of the labels or data sheets of some products is essential if you want to use it.

The best way to use this chemical for Brooklynella hostilis and Uronema marinum is as a formalin dip followed by a long term formalin bath (see environmental treatments).

To use it as a short dip in seawater, make up a bath in seawater at 200 to 250ppm for 1 hour. The dip component of this treatment regime should be carried out on days 1, 2, 3, 5, 7 & 11 after each dip the fish should be returned to a quarantine tank to which formalin has been added (see below).

For the long term bath component of this treatment, add 25ppm of formalin to your quarantine tank (it’s toxic to some invertebrates and algae, including most coralline algae species, so cannot be used in a reef situation)

Remember liquid formalin (which is how you will get it from the chemists) is 37 to 40% formaldehyde and you want 25ppm so you need to add 0.0625ml formalin per liter rather than 0.02ml to get the correct dose.

As this chemical is very toxic it is recommend that appropriate protective clothing is worn such as gloves and safety glasses and use it in a well ventilated place.

In my opinion, Acriflavin is one of the most under-used treatments available to marine fish keepers. It has a broad range of effect, being effective against protozoans, bacterial infections and external fungal diseases. It is as “reef safe” as any other “reef safe” treatment and is easily obtained. It can be bought in several formulations from the LFS but make sure it isn’t combined with malachite green or methylene blue which have toxicity issues in marine systems.

It is effective at a concentration of 6 ppm against many ciliates (Paperna, 1984) and this dose should be added to the aquarium on days 1, 2, 3, 5, 7, & 11. Your skimmer should be turned off and any activated charcoal removed. It dyes the water a greenish yellow color but after treatment turning your skimmer back on and adding activated charcoal helps remove the coloration (and do water changes).

Prescription Medicines

Flagyl (metronidazole) is by far the most effective drug available against these diseases. Indeed it is the only effective treatment for fish that are internally infected with Uronema marinum, but it has to be administered in the diet. To treat with Flagyl (metronidazole), add 34mg/l (34mg/kg bodyweight is required if treating the internal disease) of the drug to the aquarium water to be treated. A single dose should be effective, but it can be repeated daily, if required, as the drug is well tolerated by most fish. It is a very reef safe drug having little impact on invertebrates BUT it will kill off all protozoans and anaerobic bacteria in the treated tank, so, like all medications that are used in a reef tank, it will have some undesired effects on the ecological stability of the tank.


If you suspect Brooklynella hostilis or Uronema marinum then immediate action is require as these diseases progress so fast any delay can lead to losses. However, if prompt action is taken these are relatively easy parasitic infections to treat and you should be able to avoid losses. I cannot recommend enough the importance of quarantine in preventing this disease entering you reef tank.

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