Resistance to walleye dermal sarcoma tumor redevelopment

Walleyes Stizostedion vitreum infected with walleye dermal sarcoma (WDS,) v irus were rechallenged in two separate trials. Walleyes were rechallenged w ith a topical application of a cell-free dermal sarcoma tumor filtrate appl ied to the side of the fish not originally inoculated; these fish were allo wed to develop grossly visible tumors at 15 degreesC for 5 months. The rate of tumor redevelopment (calculated as incidence density) was compared with naive fish that received the same inoculum. The incidence of tumor redevel opment was significantly lower in walleyes that had previously been challen ged and infected with WDS virus. This resistance to walleye dermal sarcoma recurrence helps explain the epidemiology of WDS in the wild.