[Zbrafish] Mycobacteria

[Jen Matthews]

Hi Beth,
I have just a few things to add to the discussion on mycobacteria.  
There seems to be a lot of hype and often over reaction to the  
diagnosis mycobacteriosis in the zebrafish community.  Atypical or  
nontuberculosis Mycobacterium spp. are ubiquitous in aquatic  
environments, persisting largely in biofilms. I would argue that if  
you look hard enough, you will find it in all established zebrafish  
systems. Many Mycobacterium spp. are resistant to common chlorine  
disinfection. That's why it is also commonly found in municipal  
drinking water distribution systems and swimming pools. A number of  
these Mycobacterium spp. are documented pathogens of zebrafish,  
however, they are opportunist pathogens causing chronic infections.  
Asymptomatic carriers of mycobacteria are common in zebrafish with  
the swimbladder and ovary being the most commonly infected organs.   
There are strains of zebrafish that are more susceptible to  
mycobacteria infections.  In our experience, the TU strain is ten  
times more likely to be infected compared to other wild-type strains.  
There also appears to be some differences in virulence between the  
different species and strains of Mycobacterium.

So with this background, what do you do? I am not a proponent of  
nuking systems and starting over. You will most likely get the same  
bug back. All Mycobacterium spp. respond poorly to antibiotics, so  
this is also not a good option for fish facilities. Because of the  
opportunist nature of bacterial infections in fish, your first focus  
should be on husbandry and water quality. Stress lowers the immune  
competency of fish. This includes any type of suboptimal water  
quality (e.g. elevated nitrogenous compounds - including nitrate, pH  
fluctuations) and other stressors (e.g. high stocking density, over  
use). The other focus should be on lowering the exposure dose. All  
pathogens have a dose response - the higher the exposure to  
mycobacteria the greater the infection rate. To decrease the dose of  
bacteria make sure that your UV is properly sized and maintained,  
that cleaning procedures are adequate, and do not keep moribund  
(sick) or old fish. Eliminating Mycobacterium from zebrafish systems  
is not a realistic goal, it needs to be managed.

Let me know if you have questions. We are also always happy to give  
feedback on your husbandry and water quality parameters. very best, -Jen



Jennifer L. Matthews, DVM, PhD
Zebrafish International Resource Center
Pathology and Health Services
5274 University of Oregon
Eugene, OR 97403-5274     <(()><
(541) 346-6028 ext. 14             <(()><
Fax (541) 346-6151
jmatthews At zfin.org


On Jan 23, 2007, at 8:07 AM, Padnos.Beth At epamail.epa.gov wrote:

> I work in a facility that is trying to establish a small Medaka and
> Zebra fish colony.
> Recently we discovered Mycobacteria in our Medaka which are on the  
> same
> rack as our Zebrafish. One of the male Zebrafish  began swimming a bit
> oddly and his abdomen became red as if bleeding internally or inflamed
> organs. He is has since been set to the pathologist for screening, but
> is assumed to have Mycobacteria as well.
> The facility Veterinarian and I have both done literature searches but
> find not treatment. Has anyone successfully treated or eliminated
> Mycobacteria from their  fish and or system?
> Help is greatly appreciated from an inexperienced fish researcher.
> Beth Padnos
>
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