Pathogenicity and histopathology of an unusually intense infection of white grubs (Posthodiplostomum m. minimum) in the fathead minnow (Pimephales promelas).

A massive infection of metacercariae, particularly of the white grub (Posthodiplostomum m. minimum), was found in fathead minnows (Pimephales promelas) taken in November, 1979 from a commercial baitfish farm in Missouri. More than 2000 metacercariae were found in one fish 6 cm long. Low-grade mortality was occurring, and histologic sections showed that an intensive inflammatory response had resulted from the infection. The body cavity also contained a large volume of ascitic fluid with many blood cells, of which 92% were leucocytes. Moderate numbers of metacercariae caused a lesser inflammatory response.