http://www.atlasbooks.com/marktplc/00388mycoarticle.pdf
MB (mycobacteriosis) is considered to be the number one chronic disease in aquarium fish. MB is responsible for about half of fish deaths due to unknown causes. Because MB often has no obvious or defining symptoms, hobbyists underestimate its prevalence. If a newly purchased fish stops eating and dies after a few weeks, most hobbyists do not suspect MB (much less know what it is). Additionally, chronic MB weakens the fish’s immune system making infected fish highly vulnerable to other diseases. I wonder how many hobbyists have attributed their fish’s death to other pathogens, when the underlying problem was chronic MB?
Other MB symptoms reported in the literature are skin ulcers, emaciation, swollen bodies (dropsy), abnormal swimming, lethargy, pop-eye, abdominal swelling (ascites), abnormal skin blackening (“Black Head” disease), reduced reproduction, spinal deformities, and unnatural weight gain.
Results from the UV sterilizers were unexpected and amazing. Fish deaths stopped. A couple fish with symptoms actually recovered. Whether the UV sterilizers were killing the bacteria responsible for MB or were killing pathogens causing secondary infections was irrelevant to me. My fish were getting better!
To see how contaminated the tanks were, I purchased 8 new Rainbowfish from a trusted source. Except for one death, the fish did fine. After 8 months, a fish veterinarian examined 3 of the new fish (all Melanotaenia boesemani), one from each tank. A histological exam showed no tell-tale granulomas. The older fish had not infected the new fish. The fact that I had removed the UV sterilizers a few months beforehand made these results even more impressive.
