AKA the Gold Tetra. They produce what I believe is Guanin, which gives them their gold color. They stay small, school loosely and live a good 2+ years. I have had a group at least that long. They do lose their gold color in time, as they no longer need it as a defense against the specific parasite they exude it for.
Water parameter wise they do fine in the same conditions as most tetras, soft & acidic. Mine seemed to prefer Black water conditions in the beginning, but after a few weeks they did awesome in clear water. Love their Micro pellets.
The pic you show does not show their gold color very well. They are actually silver, but with a healthy amount of Guanin, when they are freshly caught, they are very gold, almost as gold as 10K gold.
These just arrived at the LFS. I'd like to know more about the parasite you mentioned. They seem active and friendly, like most of the Hemigrammus tetras and aren't having any major disease issues... they came from the wholesalers looking healthy and eating well.
I can't tell you much about the Guanin or the parasite. I know the parasite is external, and that the Guanin is exuded specifically to prevent that parasite from infecting it. I know that if you breed the tetra, the fry do not have Guanin exuded in thier scales. Also if you keep them long enough, they will lose thier Guanin.