Bacterial Fin Rot

[Rondelet]

Having observed this pair of butterflies closely for a couple of weeks now, I'm pretty certain they are dealing with bacterial infection. The left fish (file-"œRaccoon-01") is lagging behind the second fish as there is only a small notch on the posterior of the dorsal fin. This shot essentially show the very start of the infection. The right fish (file-"œRaccoon-02") shows a more advance progression with much of the posterior portion of the dorsal and anal fin missing, along with some splitting of the caudal fin. The fins on the second fish have been slowly deteriorating for a few weeks now. What is particularly interesting is that there are no other signs of disease. The margins of the fins at the site of infection show little to no signs of inflammatory response. Fish are swimming around normal, eating very well, and show no other signs indicating septicemia (although this could change!). My apologies for the image quality. I was trying to get a close-up of the fin margin with a macro, but my lens is not great (quite slow) and the fish are very active.

I've tested the water and get no readings for ammonia. I have been cleaning the tank to remove detritus and changing the water (10 % weekly). The bioload is very minimal with only a few other fish: a midnight angel and royal gramma, both showing similar signs of the same type of fin damage but also doing well otherwise; there is also a sailfin tang, goby and flame angel all showing no signs of disease. The system is 120gal with a 20 gal sump.


It would be next to impossible to remove the fish without taking all the live rock out. Given that the system is a simple FOWRL, I'm preparing to treat the system with erythromycin and tracking the results. I'm curious to know if anyone else has observed a similar pathology in their fish: fin rot without obvious signs of inflammation and no other signs of disease. Any comments or observations are welcome.

 

[HumbleFish]

I've seen this before. It's a gram positive bacterial infection which I have successfully treated with erythromycin. But the problem with erythromycin is it's very slow acting. You may need to treat for a prolonged period of time to completely knock this out. Erythromycin will also have minimal impact on your anaerobic bacteria, so you are good to go there. Finally, I would suggest running a UV (if you have one) to prevent the bacterium from spreading any further.

 

[Rondelet]

Thanks for the feedback, most helpful.

I was thinking the same thing, re Gm+ bacteria. I came across this before in a puffer but had no lab work up/confirmation. Did you do any microbiology to confirm this? I lost butterflies in the past to bacterial infections, but the lab worked came back Gm-. In those cases the fish showed very obvious signs of inflammation and a more classic response to septicemia. This case is different and I'm wondering if the bacteria involved have some kind-of immunosuppressive property.

Following treatment I will update the post accordingly.

 

[Rondelet]

...erythromycin is it's very slow acting. You may need to treat for a prolonged period of time to completely knock this out. ...

I was planning on dosing at 200 mg/10 gal (~5 mg/l), 4 times at 24 hr intervals; water changes after the 2nd and 4th day as per the API recommendation. What dose/duration did you use?

I've been doing some reading and came across a longer schedule, 10 days. I've also seen higher dose rates (12-24 mg/l), but no specific duration. As well, I've come across concerns over affects on nitrifying bacteria with prolonged exposure.

Any comments/experiences would be appreciated.

 

[HumbleFish]

Most of the time you have to double the dosage for s/w fish; so 400 mg/10 gal. I've only used 200 mg/10 gal as a prophylactic and for very mild infections. I generally do a 5 day course, 25% WC and then another 5 day course (if needed). If that doesn't knock it out, then it's time to move on to something stronger such as Nitrofurazone and Furazolidone.

Both the 200mg and 400mg dosage will kill some nitrifying bacteria, but not enough to cause an ammonia spike IME.

 

[Rondelet]

Thanks for the feedback. Just to clarify, are you dosing 400 mg/10 gal each day for a total of 5 daily treatments?

 

[HumbleFish]

400 mg/10 gal each day

Yes