Prophylaxis for chromis (and other Uronema prone fish)


Dr. Fish
HF Vendor
Navarre, FL
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Enough is enough! After encountering recent failures to eradicate uronema via metronidazole, acriflavine and FW dips; I highly recommend using formalin to pretreat any chromis and other Uronema prone fish. Anthias are also very susceptible, but I sometimes see Uronema on damsels, clownfish, butterflies and angels.

Any fish you suspect is carrying Uronema should get a 45-60 minute formalin bath before entering your DT or QT. Do the following:
  1. Buy 37% Formaldehyde which also contains 10-15% methanol as a stabilizer. Amazon sells it here & here.
  2. Buy waterproof gloves and a face mask. To prevent your skin from coming into contact with it and to protect your lungs from the fumes.
  3. Use a bucket or small aquarium to perform the 60 minute formalin bath. Temperature control the water by using a heater. It is very important to heavily aerate the bath for at least 30 minutes before and also during treatment to compensate for oxygen depletion. The fish should be placed in a premixed bath solution. DO NOT add more formalin after the fish is already in the bath.
  4. Dosage for the bath is 0.6 ml per gallon, or 12 drops per gallon.
That should do it for Uronema (and Brooklynella). No further treatment required (for those two diseases!) Formalin will also eliminate any flukes (but not the eggs), and provide temporary relief for Velvet. Experimentation with using H2O2 to treat Uronema is ongoing, but efficacy hasn't been proven yet.

DO NOT use formalin (or H2O2 for that matter) on fish with open sores/wounds. It will burn them. This treatment is designed to treat fish who are carriers (light infestation) of Uronema. If you see active red sores on a chromis, humanely euthanize the animal:

If you have an aversion to using formalin, I would just avoid chromis altogether. It's not worth getting a free living parasite in your aquarium that going fallow will not eradicate. Uronema in high concentrations can affect ALL FISH; attacking the gills, viscera and body muscle.

There is anecdotal evidence (but never scientifically proven) that some fish exposed to formalin don’t live past 18-24 months. In some areas, the purchase of formalin is prohibited.

If you need confirmation of Uronema, take a skin scrape of the affected area and examine under a microscope. Compare to what you see below:

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