Michigan Department of Conservation
Institute for Fisheries Research Report No.1712, 1966
The Redworm of Yellow Perch in the Great Lakes
Leonard N. Allison, Fish Pathologist
Abstract.-Many fishermen are finding redworms about an inch long in the body cavity of perch from certain areas of the Great Lakes. This worm is a nematode (Philometra cylindracea) that lives normally as an adult in the body cavity of yellow perch. The female worm releases tiny live larvae which reach the water and infect a small water organism. The organism called Cyclops is suspected as the one involved here. The larvae develop in the body cavity of the Cyclops to a stage infective to perch, and the fish become infected when they eat the Cyclops. Twenty-five collections of perch made from 1956 through 1964 included 2,028 perch from 16 locations in Lake Michigan, Lake Huron and the Detroit River. No infested perch were found in the Lake Michigan collections from Ogontz Bay, Big Bay de Noc, Garden Bay, Sturgeon Bay, or at Ludington and Saugatuck. Collections from the Straits of Mackinac near Cheboygan were also negative. In Lake Huron, infestations were high from Alpena southward to Saginaw Bay. A rather low rate of infestation was found in the Detroit River. In the areas where collections were made for more than one year, infestations in the Pinconning, Tawas Bay, and Alpena areas increased from 1956 through 1964, whereas infestation remained at zero in the Cedarville area.
The redworm is readily removed from perch when the fish are cleaned. It does not affect the eating quality of the fish and is not harmful to human beings.