The Bacterial Infection Predicament

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Dr. Fish
Navarre, FL
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The Bacterial Infection Predicament

Please do not view the information below as a shortcut to quarantine. Use it only in an EMERGENCY SITUATION when treating a fish with parasites/worms PLUS a serious bacterial infection.

So, your fish has a nasty bacterial infection. :eek: You've treated with antibiotics for 10 days and it's still not looking any better. What gives?!

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Photo by: ngoodermuth​

Why fish get bacterial infections - We all know the water in our aquarium is full of bacteria. Most of it is good (like nitrifying bacteria), but some can be bad and harmful to marine animals. The bad kind is usually kept at bay by a healthy fish's natural immune system. Or if the fish becomes "sick" and displays symptoms of a bacterial infection, many times the immune system is still able to fight it off without the aid of antibiotic medication. So if you stop and think about it, these bacterial infections in fish are akin to our own never-ending battle with germs, viruses, and of course, infections. :rolleyes:

Many factors make a fish more susceptible to infection. First, a cut or open wound is usually required for infection to set in. Even tiny exit wounds left by feeding parasites or worms can get infected. Poor water quality can be a contributing factor as bacteria seem to prefer dirty wounds. ;Sour Also, anything that lowers the fish's overall immune system makes infection more likely. Stress (e.g. fish fighting), malnourishment, or if the fish is battling an ongoing parasitic (e.g. ich, velvet) or worm (e.g. flukes, turbellarians) infestation makes a "secondary" bacterial infection probable. For example, back when I practiced "ich management" it seemed periodically I would have a fish develop “popeye” or some suspicious red mark. Now that I quarantine (QT) and prophylactically treat all my fish, I almost never see anything like that once the fish enters my display tank (DT). Disease-free fish are healthier fish and more capable of overcoming potential infections. In any case, it's these "secondary" infections which cause the predicament which is the subject of this article.

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Photo by: Chicago​

The Predicament - So, your fish has ich or velvet PLUS a bacterial infection. :eek: Friend, you've got a serious problem on your hands. :( In most cases, treating for the parasite takes precedence over the bacterial infection - this is especially true when dealing with Marine Velvet Disease. However, the two chemicals most commonly used to treat ich & velvet - copper and Chloroquine phosphate - are both immunosuppressants. So while these are working to eradicate the parasites, they are also suppressing the strength of the fish’s immune system, thus reducing it's capacity to fight off whatever infection is afflicting your fish. Remember, antibiotics, in and of themselves, do not cure a fish. Antibiotics merely control the population growth of bacteria in a fish long enough for its immune system to eliminate them. In all cases, proper nutrition will play a critical role in helping your fish overcome infection. It is very important to feed vitamin enriched foods and ones which contain probiotics when your fish are sick. Proper nutrition + medication is a 1-2 punch to help combat illness and disease.

What to do for Ich + Bacterial Infection - Tank transfer method is your best option in this situation because no chemicals are being used to eliminate the parasites. So, you can freely dose antibiotics in conjunction. You'll have to time your dosages just right so as to not waste the medication(s); but remember most antibiotics dissipate out of the water after 24 hours anyway. ;)

Hyposalinity would be my second choice, only because hypo resistant strains of ich have been proven to exist (study done by Yambot in 2003.) However, being no chemicals are used you would dose antibiotics for a minimum of 10 days in conjunction with hypo.

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Photo by: Jordan Berry​

What to do for Velvet + Bacterial Infection - This is the worst predicament to be in, and unfortunately often the most common. :( Due to the severity of velvet, the use of copper or Chloroquine phosphatemust commence ASAP. Antibiotics can still be dosed in conjunction, but appetite suppression will likely increase and additional gas exchange must be provided to compensate for the added oxygen depletion. It is also possible that you will encounter a bacterial bloom from combining too many meds. To counteract this, use an air stone or point a powerhead towards the surface of the water in order to supply more available oxygen to your QT. Other tips for accomplishing this are discussed here:

Unfortunately, oftentimes combining antibiotics + copper/CP will only keep an infection at bay, or it might even get worse. Sometimes using an herbal remedy (such as Melafix) is a wiser and more cost effective option at this point, to just boost the immune system until proper antibiotics can be administered without copper/CP in the water (described below). Another thing you can do to help is give the fish periodic baths using an antiseptic (acriflavine is a good choice). This should slow down the progression of the infection. However, it is imperative to get the fish out of copper/CP ASAP so that antibiotics can be dosed without the immunosuppressant being present. The protocol below explains how to best accomplish this, but also allows NO MARGIN FOR ERROR. Everything must be done exactly as stated:
  1. Give the fish a 5 minute freshwater dip, followed by a 90 minute acriflavine bath in saltwater.
  2. Place the fish in QT, and raise copper or Chloroquine to therapeutic levels. With Chloroquine this can be done immediately, but for copper it is best to take 48 hours (for velvet) to reach therapeutic.
  3. You'll also want to start dosing an antibiotic or an herbal remedy (such as Melafix) to contain the infection.
  4. Once copper/CP has reached full therapeutic (very important), begin a 5 day countdown. On Day 5 (although waiting a little longer is always better if the infection doesn't look too bad), transfer the fish to a non-medicated holding tank at least 10 feet away from the QT (more info regarding aerosol transmission). DO NOT reuse ANYTHING from the QT for the holding tank; only transfer the fish. The fish should be velvet free following the transfer, because within 4 days any remaining trophonts will drop off the fish. The presence of copper/CP will shield your fish from reinfection and any unhatched tomonts will be left behind in the original treatment tank. ;)
  5. Now that the immunosuppressant is out of the way, it's time to get serious about knocking out this bacterial infection. Antibiotics are notoriously slow acting in fish, so continuous treatment for 10-14 days is usually required. Below are two wide spectrum antibiotic regimens I use:
  • Combining Kanaplex + Furan-2 + Metroplex
Only treating with copper or CP for 5 days is cutting it very close, and only works if you can transfer the fish to another tank at least 10 feet away. Therefore, it would be wise to observe for an extended period of time (4-6 weeks) to ensure velvet is really gone. Also, both copper/CP treatment (QT#1) and followup antibiotic treatment (QT#2) are best done in a rockless/bare bottom tank - as sterile an environment as possible.

** This treatment protocol also works for ich + bacterial infection; however for ich, the fish must be in therapeutic strength copper or CP for at least 8 days before transferring. However, I prefer a 10 day transfer just to allow a little more wiggle room. :)

What to do for Brook & Uronema + Bacterial Infection -
  1. Give the fish a 5 minute freshwater dip (optional).
  2. Followed by either a 45 minute formalin bath or 90 minute acriflavine bath in saltwater (highly recommended).
  3. Place the fish in QT, and treat with this combination of meds for 10-14 days: Kanaplex + Furan-2 + Metroplex. Since uronema can also infect a fish internally, fish food should be laced with metronidazole for 10-14 days as well. Use Seachem Focus to bind the medication to the food, to prevent it from just leaching out:
What to do for Worms (flukes, turbellarians) + Bacterial Infection - You can dose Prazipro in conjunction with most antibiotics (but only in a QT). However, Prazipro will sometimes interact negatively with other medications due to the Oxybispropanol it contains. The main thing you'll want to watch out for is a bacterial bloom (very cloudy water). A severe bacterial bloom can starve all oxygen out of the water and cause your fish to die due to asphyxiation. :eek: Adding an air stone or pointing a powerhead towards the surface will sometimes counteract this by providing more available oxygen. However, it is always prudent to keep freshly mixed saltwater on hand to perform a large water change if needed. DO NOT add more medication(s) to the water until after it has completely cleared.

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Photo by: JP 75​

Final thoughts/disclaimer - Some of the methods described above offer less than ideal solutions. In particular, only treating with copper/CP for velvet (for 5 days) or ich (for 8 days) is probably cutting it too close for comfort. (As stated above, a few extra days in copper/CP would be better.) The science behind it is sound, as velvet trophonts can only remain on a fish a maximum of 4 days, and 7 days for ich. And so long as copper or CP has been maintained at therapeutic levels the entire time, any free swimmers would not be viable by the time they reached a fish. However, this method does not take human error into consideration (e.g. you forget to test your copper level one day), and attention to detail is required to ensure precision. For these reasons, I struggled with whether or not I should be recommending what I have outlined above, but in the end, I could not in good conscience withhold scientifically accurateinformation which could potentially save a fish's life. After seeing how many fish were dying in copper due to secondary bacterial infections, and knowing that many gram-negative infections can kill within just a matter of days... I felt it was necessary to recommend a more aggressive treatment strategy whenever a secondary infection is also in play. To be clear, I consider the above only a stopgap measure until better methods can be developed. Indeed, finding more effective treatments for bacterial infections is high on my priority list. I feel we (as a community) are getting better when it comes to treating parasites and worms but still lacking when faced with a gram-negative bacterial infection afflicting a fish. This is unacceptable :mad:; there HAS TO BE a better way. ;Bookworm ;Doctor