I always wondered this as well, plus once on one fish will they drop off or attach to another fish or something else. Or is this when the Birds come in and eat the fish then the parasite starts over either from falling out of the mouth or passing through the system.

Also do these parasites first start on the outside and then move into the flesh or the other way around.

Has anyone ever caught a RES that had the parasite? Why do they not get them from eating the infested snail?

Thanks