Trout Parasites
From the ODFW page,
Copepod
Copepods are common in fish and found throughout Oregon. Usually there are few parasites present on fish and they go unnoticed, however occasionally they can become numerous and quite evident on gills, in the mouth and at the base of the fishs fins. When present in extremely high numbers they can cause a fish health problem but this is rarely seen in the wild. The parasite poses no risk to humans or domestic animals.