Bacterial External Infections, Columnaris (specific to F. columnaris); Often Misnamed "Mouth Fungus", Fish Tuberculosis/TB Skin Infection (specific to Mycobacterium spp.)
Pathogen/Cause: Various organisms. Positive diagnosis not possible outside of lab culture & microscopy (not practical for most hobbyists). Gram positive: exceedingly rare in FW fish; small handful of SW species, but most primarily do not attack skin. Gram negative: Flexibacter columnaris, Aeromonas spp., Pseudomonas spp., Vibrio spp., Salmonella spp., many others not listed. Non-stainable: Mycobacterium spp., mostly M. piscium & M. marinum
Physical Signs: White, clear, red/pink areas of necrosis. Occasionally slightly ragged/fuzzy appearence. Inflammed patches and sometimes deeper ulcers develop. Various patterns of appearence and presentation. Columnaris usually presents near the head and sides of the body and is often mistaken for a fungus; it is characteristically white and patchy.
Behavioral Signs: Various: lethargy, hiding behavior, "hanging", clamped fins, loss of appetite, general constitutional signs.
Potential Treatment: Broad spectrum antibiotics. (Examples include but are not limited to: Maracyn I & II, Jungle Binox, Aquatronics Kanacyn, etc.). Frequent water changes a must to improve quality. Tuberculosis is difficult to treat because it attacks intracellularly.
Other Notes: Frequent water changes a must to improve quality. Test for ammonia, nitrites, nitrates. Columnaris perhaps one of the most common skin infections of pet fish (livebearer fish and certain other fish especially susceptible). Specifically for F. columnaris, read this article by Dr. Barb. Fish tuberculosis (though not transmitted by the same species that causes human tuberculosis) can be transmitted as zoonosis called "fish tank granuloma" on hands with open wounds (again, another article by Dr. Barb discusses this issue. Use gloves if reaching in the tank with suspect animals.
