This is a video of a parasite, commonly known as eye flukes, swimming in the eye of a sucker in our lab. The eye fluke has a complex three-host life cycle involving birds, snails, and fish. The parasite travels from bird to snail when the birds poop, from snail to fish when the snails shed the parasite, and from fish back to bird when the fish are blinded by the eye fluke and eaten by water-faring birds. This video is highly unusual as the parasite is usually inside the eye instead of swimming on the surface.  

This United States Geological Survey news article "Congratulations to Genevieve Kent for Winning this Issue's Photo Contest!" was originally found on https://www.usgs.gov/news