Volume 4, Issue 12
Figure 1. Northern pike from Lake Champlain, VT showing external tumors caused by Esocid Lymphosarcoma. Image from T. Jones, Vermont Fish and Wildlife Department.
Lymphosarcoma of pike has been recognized for over 80 years. It affects pike and muskellunge in Europe and North America. External signs of tumors include protruding growths on the flank, fins, and head that are several centimeters in diameter and have irregular surfaces. Tumors can also occur on internal organs including muscle, kidney, liver, and heart. External tumors can be present during any season, however, they are most commonly seen in the fall and winter months. Tumors vary in color from grayish-white to pink or red depending on the amount of vasculature associated with the mass. Young tumors are usually more white and as they mature and grow, they must attract blood vessels to supply their nutritional demands.
There is not much information available regarding the effect the tumors have on pike behavior. It kills pike that have severe infections; however, many of the pike observed with Esocid Lymphosarcoma are caught by anglers. A 2002 northern pike fish kill on Lake Champlain, VT was caused by Esocid Lymphosarcoma. Research on the virus has been unable to determine the morbidity and mortality characteristics of this virus. No research to date has been able to culture the virus invitro. Histologically, tumor cells resemble lymphocytes but are usually twice as large.
Figure 2. Histological section from tumor of Northern Pike . Lymphocytes (black) multiplying and invading fish’s dermis (red whorls).
It is not known if the disease can affect other species of esocids like Maine’s popular chain pickerel (Esox niger). There is no treatment for the disease in pike or muskie. Preventing the spread of Esocid Lymphosarcoma means preventing the spread of infected northern pike and muskellunge.
Special points of interest:
Fish with Esocid Lymphosarcoma cannot transmit the disease to people.
Esocid Lymphosarcoma is caused by a virus.
Esocid Lymphosarcoma has not been found in Maine.
For more information read: K. Wolf. Fish Viruses and Viral Diseases 1988, 389-398.
Images were made possible by a grant from the Maine Outdoor Heritage Fund.