Parasite Living Inside Fish Eyeball Controls Its Behavior

In case you need a little more nightmare fuel, scientists have been studying a fish eyeball parasite. Diplostomum pseudospathaceum infects a fish's eye as a larva. While the larva grows, it causes the fish to swim slower than usual, which protects both the fish and the parasite from predators. But when the larva is mature, it makes the fish swim faster and closer to the water's surface. That's so the fish will be eaten by a bird!

The eye fluke Diplostomum pseudospathaceum has a life cycle that takes place in three different types of animal. First, parasites mate in a bird’s digestive tract, shedding their eggs in its faeces. The eggs hatch in the water into larvae that seek out freshwater snails to infect. They grow and multiply inside the snails before being released into the water, ready to track down their next host, fish. The parasites then penetrate the skin of fish, and travel to the lens of the eye to hide out and grow. The fish then get eaten by a bird – and the cycle starts again.

The current research is about fish eyes that contain both mature and immature parasites. How do those fish act? Read about Diplostomum pseudospathaceum at New Scientist.