Fish Tuberculosis

Fish tuberculosis is caused by a member of the mycobacterium genus known for tuberculosis in humans. This genus is unique, in that its cell wall is formed from different materials than any other bacteria in the world. This means that it is neither gram positive nor negative. Because of this unique property, it is able to evade most of the common antibiotics in use throughout the world. Even in humans, treatment involves more of symptom control than disease control so that the body's immune system can deal with it. Tuberculosis, in fish and humans, is best treated by preventing it. 

Like pathogenic bacteria in the aquarium, fish TB is best prevented with "over filtration". This is due to the fact that most, if not all, pathogenic bacteria are opportunistic and will only cause problems if there are certain conditions that allow them to overpopulate or to thrive inside of a fish. an overabundance of filtration allows for bacteria more bacteria to find homes that aren't the fish as well as providing enough ideal space for more beneficial bacteria that will fight the malicious bacteria before it can reach infectious levels. 

It is worth noting that fish TB is zoonotic, meaning that it can infect humas too, though this only happens if you put your hand, with an open wound, into a tank with a certain number of bacteria present. I'm dumb enough to regularly stick my hand (with open wounds) in my fish tanks (that undoubtedly have fish TB) and I haven't caught it. It is worth being aware of, as it can show up as red abscesses in affected area, which can be worrying. A doctor can make a more meaningful diagnosis if they know that you keep fish, should something like this pop up.

Symptoms

Tuberculosis was called consumption for a reason. Its main areas of attack tend to be the digestive tract and muscles. As it "consumes" the fish, you will notice Sunken Belly, weight loss, lethargy, lightening of color (indicative of stress), and Clamped Fins, and hemorrhagic lesions (open/bleeding wounds). As the disease progresses, deformities will occur in the fish, as pictured. Mostly, the muscles that keep the spine straight will wither away and cause some nasty lordosis, which the fish might recover from, but the spine will likely never reform properly. At that point, a serious consideration of quality of life needs to be done, as euthanasia might be the best course of action. Vitamin C Deficiency can also cause similar deformities, and should be looked into alongside fish TB, as vitamin C is known to be a critical nutrient for immune system functioning. 

Treatment

While most antibiotics will not work with a mycobacterium, there is some evidence that a certain antibiotic duo can be effective when used in tandem with a UV sterilizer. Mycobacteria are resistant to pretty much any other antibiotic, so the typical doxycycline and erythromycin combo just won't cut it.