mr. Fish is dead. Hopefully not without providing some important info, but I am sure that my minimally invasive treatments did not kill him outright.
For your consideration:
Remaining fish population (1 tank):
4 Neon tetras, incl, 1 mature female, 2 mature males and one undetermined-gender adolescent.
3 Swordtails, incl, 1 mature female and 2 mature males.
5 zebrafish incl. at least 1 mature female, two mature males and two undetermined-gender adolescents.
The dead specimen is a mature adult, suspected male, possibly senescent.
Up-close observations: It has 1 brown fiber/hair/spine-like projection from gill, and several from anal fin area; more possibly from tailfin, depending on whether the observed odd-coloration is, in fact, atypical of species markings.
No such darkened protuberances are visible on any of the remaining live fish, however this could be due to the inability to get close enough for adequate inspection (20 gal. tank).
My "gut" feeling, based on observations on individual, living fish: at least two of the remaining four tetras have established infestations, as well as at least one zebrafish (and if the aforementioned "mass" is in fact the infectious element/vector/pathogen, then the female swordtail is infested as well. She was observed to be actually attacking the potentially infectious mass this afternoon.)
Before expiring, white mucoid substances (worms? hairs?) were observed to be sloughing off the originally-mentioned tetra. I am maintaining the deceased tetra's body in the original treatment jar, in order to observe the progression of decomposition, with zero additives to preserve or otherwise deter the natural progression of events within the existing environment.
There are many details of questionable significance. Will post details and pics as I am able, but, respectfully, tired of wasting time uploading and posting in two locales..