Bacterial pathogens are common in fish aquaculture but have been rarely diagnosed in the aquarium hobby. Our tests have revealed that a few known pathogens show up in a small fraction of hobbyist tanks. The most commonly encountered are Vibrio fortis and Photobacterium damselae.
Both of these pathogens seem to affect a limited range of fish in the aquarium hobby (V. fortis is a pathogen of seahorses and their relatives, while P. damselae affects a somewhat broader range of fish including the Damsel family). So the fish in your tank may not be susceptible. Some types of P. damselae are more pathogenic than others, and our test cannot distinguish between these types. So its possible that the type present in your tank could be a less pathogenic variety.
Despite these uncertainties, most reefkeepers would be rightly concerned to find a known fish pathogen in their tank. We’ve started a discussion on the topic here.
While we cannot offer specific advice for treating your fish (which would constitute veterinary advice), our practice is to remove symptomatic animals from the tank whenever possible, transferring them to a separate quarantine tank (QT) for observation. This removes a major reservoir of the pathogen from your tank.
If you choose to treat fish, this can be more easily done in the QT. You can find an excellent discussion on some of the options for treating bacterial infections in saltwater fish here.
We generally do not recommend antibiotic treatments on the display tank, for a variety of reasons. If you find a bacterial pathogen in your tank, we suggest the following general strategy, modified as needed depending on the details of the situation.
- Remove the main source of the pathogen from your tank. This may involve transferring a symptomatic fish to QT or trimming dead parts off a coral colony. Better to lose an individual fish or coral than all of them!
- Deep clean the tank. Many pathogens persist in biofilms and sediments. Scrub the glass, vacuum the substrate, and do a series of relatively large water changes (up to 50% of the tank volume).
- Maintain relatively low nutrients (no more than 5 ppm nitrate) for a while to avoid feeding a bloom of pathogenic Bacteria. Maximize nutrient export (e.g. run your skimmer or refugium lights for a longer period).
If your fish don’t show any symptoms, its perfectly reasonable to do nothing. Some groups of fish are less susceptible to particular pathogens, and individual fish can develop resistance over time. A pathogen in your tank may pose little risk to the fish that currently exist in your tank, but a major risk for susceptible new introductions. In that case, you may wish to avoid adding fish from known susceptible groups while the pathogen remains in your tank.