The other day I brought 3 rummynose tetras home from the shop and placed them with my existing longfin zebra danios.
3 days later, I noticed that one of the fish had a milky section about halfway along its body, and another had turned almost completely milky throughout. The third fish continued to be transparent. I euthanised the 2 infected ones as they were suffering.
I am wondering what this could have been. Someone suggested mycobacteria (fish tb) but that is supposed to develop slowly, with hollow bellies and open sores. I am also suspecting Neon Tetra Disease which, I have heard, has milky areas that can grow.
Can anyone settle this debate? Here are four photos
Regular one:
The one with the milky section:
The one that was all milky:
Milky fish 
