Native Son- a large percentage of salmon with tumors would be a BIG concern to me. They are realtively short-lived (3-5 yrs) when compared to other fish species. Age is certainly related to tumor incidence as is exposure to some classes of pollutants. To see a significant number of tumors (benign or malignant) would to me indicate that somewhere in early development these fish were possibly exposed to some real nasties...a lower frequency of tumor formation could certainly be genetic pre-disposition or "normal" for that race of fish.