Clinostomum marginatum is a species of parasitic fluke (class Trematoda). It is commonly called the "yellow grub". It is found in many freshwater fish in North America, and no fish, so far is immune to this parasite. This type of fluke can be found in the mouth of aquatic birds such as herons and egrets. They are also found commonly in the esophagus of fish-eating birds, and reptiles. Eggs of these trematodes are shed in the feces, hopefully into the water. Many aquatic birds become infected by ingesting freshwater fish that are infected. The metacercariae are found right beneath the skin or in the muscles.