Flukes are often called the Gift that keeps on Giving.. Because discus can harbor them with absolutely no symptoms..Its next to impossible to know if your fish have them without gill scrape/snips and microscope. Over time with stress and poor water , over crowding etc. what was a low level infection can flare up and the flukes overwhelm the fishes immune system..."all of a sudden" they have flukes as they are flaring gills and flashing off things... I say all of a sudden but obviously they were there all along.
to make it harder to treat and diagnose... 99.9 % of the time flukes are diagnosed solely by symptoms which gives rise to many problems such as meds reportedly "not working" or resistent strains develop from the incorrect use of meds.
There are technically 2 kinds of flukes for fish.. Dactylogyrus aka gill flukes ..These reproduce by eggs . Then theres Gyrodactylus, skin flukes which reproduce in a crazy fashion akin to live birth... there is a fluke within a fluke with in a fluke ready to hatch.
https://www.simplydiscus.com/library...ematodes.shtml
Its unlikely gyrodactylus would be spread by food... but there is a theoretical possibility that Dactylogyrus could as their eggs are pretty resistent. Its also thought at least by some that some flukes are species specific. I believe that Untergasser thought that some species of flukes could be carried by other fish species and infect discus in a low level way, but other species would be harder on the fish...I am paraphrasing and not 100% on this .. It would make sense as there are many species of flukes.
https://www.sciencedirect.com/scienc...20751922000340
The salt dip I mention is a non-specific mechanical treatment for external freshwater parasites like flukes.
al
In this case