Very few fish in running waters die from ich but those in small ponds sometimes do, especially overcrowded aquaculture ponds. Here is why, the life cycle of theich parasite means that the mature organism must dorp off the fish to reproduce , in currents and large bodies of water the fish and the new motile parasites are usually no longer in the same area so few parasites find hosts before they die, also there are myriad organisms like mysid shrimp, planaria, ameoba, and even daphia that will eat the free swimming parasites or even the encysted stage on the substrate, it is only in recycled and over crowded waters that you are likely to see a major infestation.
