I don't see any signs of a fish having a parasite, my fish are all very healthy and none are thin, my loaches are normal, my peacock gudgeons are fat and have a lot of eggs in them (I have all females), my plecos don't have a sunken stomach, my tetras and barbs aren't thin and emaciated, and my shark is doing fine too, I really have no Idea what it could be that has parasites if any, I think it might be from my plecos because I don't know any other fish that can poop like that, it looks like it's more clear with something green/brown in it than white though
"sign of the parasite" would be the stringy white poop. Again it could be something else causing it (clear and white are used interchangeably in this description) but the first thing I think of would be hexamita. This could also be the only sign at this stage; lack of other symptoms don't mean your fish are clear. I would monitor them and if you see more poop like this, try feeding food soaked in Epsom salts; this is a natural laxative and remedy for hexamita. I would also keep water extra clean if possible.