Everyone that keeps fish - whether in a pond or aquarium, needs to know about Mycobacteria!  It not only affects a wide range of fish species (including Koi and goldfish), but it's one of the few fish diseases that affects humans as well!  While it's not curable in fish, in humans it requires many months of treatments.  This video from Fish Vet Dr. Richmond Loh will tell you everything you need to know - but I'll add one more thought - if you have any open sores on your hands, or if you are handling a sick fish - USE GLOVES!

Watch the video - runs ~ 15 minutes, and WELL WORTH IT!

https://thefishvet.com/2019/03/12/is-your-fish-infected-with-mycobacteria/

Source: TheFishVet website of DVM Richmond Loh, Australia:  https://thefishvet.com/