Blood Parasites (Trypanoplasma, Trypanosoma, Sanguinicola)

Not really obvoius but could be one or more of the following. Anaemia, emanciation, gill damage, kidney damage, pop-eye, and/or listless behavior.
Trypanoplasma, Trypanosoma, Sanguinicola, and other protozoans.
A carrier or host to help the introduction into the aquarium. Usually freshwater snails.
There are a few medications on the market for these parasites but to increase their affectiveness you should also eliminate snails or other leeches from the aquarium. It is best to try and get them all by hand. Most snail removal products are not that great and can also be harmful to some fish.
Lifecycle of parasite Length varies depending on on the specific parasite.

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