also known as: eye fluke, diplostomum
Diplostomum are digenean trematodes that have complex life cycles that involve birds (usually gulls), snails and fish. Diplostomum species are common parasites throughout North America and Europe. Many fish species can become infected, including both warmwater (e.g. channel catfish) and coldwater (salmonids) fishes. Infections have been reported in amphibians, reptiles and humans.
In fish, the parasite infects the eye and can led to modifications of the host's behavior, which can make it more likely to be eaten by the parasite's next host (a fish-eating bird). The parasite also affects marketability of the fish, affecting its feeding and growth, cosmetic appearance and causing blindness. There have been cases of blindness in hatchery populations of coho on the Columbia, in asociation with the large (and infected) populations of the parasite's alternate host birds and snails.