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Treating Marine Fish
for Bacterial Diseases

Racoon Butterflyfish with a cloudy eye.Racoon Butterflyfish after treatment.

Before and after pictures of a Raccoon Butterfyfish (Chaetodon lunula).  After three days of treatment the eye on this fish was clear again.

By Tony Griffitts

Effectively treating bacterial diseases in saltwater fish is more difficult than freshwater fish.  Through experience and experimentation in trying to treat many bacterial problems in saltwater I have come up with a procedure that is very effective, and will cure most common bacterial problems in marine fish.

Bacterial problems most often occur within 2 weeks of a being introduced into a new aquarium.  The most common problem I encounter is cloudy eye with Angelfish and Butterflyfish, but it can also occur less commonly in other marine fish.  If you allow the cloudy eye to go untreated it can turn into pop-eye.  Fish injuries due to scrapes or aggressive tank mates can also open fish up to bacterial infections.  It is important to catch the infection early and treat aggressively.

First, you will need to set up a quarantine tank, if you do not have one set up already.  A quarantine tank can be any size, but usually 10 to 30 gallons depending on the size of your fish.  The smaller the quarantine tank, the less medication you will have to use, and the fewer gallons of water you will have to change out.  Filtration can be as simple as a sponge filter or external hang on the back filter.  It is important that no activated carbon be used in the filtration, as it will pull medications out of solution.

In the quarantine tank, reduce the salinity to 1.011 to 1.012.  I have found antibiotics  in-effective in full strength seawater.  Remove the infected fish to the quarantine tank.  Don't worry about the difference of the salinity, as I have not found any problem with any fish making the transition to this low of a salinity. 

My antibiotic of choice for marine fish is a sulfa based medication like Mardel's Maracyn Plus (Sulfadimidine [aka. Sulfamethazine], Trimethoprin), or Triple Sulfa (Sulfadiazine, Sulfamethazine, Sulfamerazine).  The medication must be double the dose of what is recommended on the package for freshwater fish.  Add the double dose of antibiotic every day for 3 days, and then do a near complete water change with the new water being the same salinity (1.011 to 1.012).  Treat again for 3 days, with a near complete water change after every 3 treatments.  Usually after 5 days of treatment you should notice that the infection has shown some improvement, and in some cases it may look completely normal.  I recommend that you continue treating for at least 7 to10 treatments, or 2 days past after the fish no longer shows any sign of infection.

After completing the treatments, do a near complete water change. During the next two days, slowly increase the salinity to that of your display tank.  I have noticed some unexpected fish loss (mostly with Angelfish) a few days after the fish were returned to full strength seawater when a slow acclamation process was not observed.  Keep an eye on the fish for the next few days making sure no re-infection occurs, then return the fish to your display tank.

Chalk Bass with Pop Eye.Yellow Tang with Pop Eye 4 days into treatment.

This Chalk Bass (Serranus tortugarum) (left) has pop-eye that can be treated with antibiotics.  This Yellow Tang (Zebrasoma flavescens) (right) is 4 days into treatment for pop-eye.  The bubble above the eye is common when the swelling begins to recede, this will be completely gone in a few days.

With this treatment procedure, I have been able to cure most marine fish, including a severe case of pop-eye in a Long-nose Butterflyfish (Forcipiger flavissimus).  These procedures were developed over several years of treating marine fish with many different antibiotics and salinity manipulation.

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