Intestinal worms in fish don't come from plants. They come from Asian fish farms that regularly grow ornamental aquarium fishes in sewerage ponds, or they grow daphnia (small crustacean) in sewerage ponds and feed the daphnia to fish. The fish get worms from eating the infected daphnia and pass it on to each other. The ponds containing fish have the fish removed and sold before more fish are added. So worms and worm eggs are left in the pond to infect new fishes being put in the pond to grow. Most aquarium fishes coming from Asian fish farms are regularly exposed to, and or infected with intestinal worms.