A marine fish diet reduces spontaneous lymphoma in outbred Swiss-Webster mice

Diets rich in marine organisms or their oils are known to suppress solid tumor development in humans and rodents, but the potential for marine foods to affect hematopoietic system cancers is not well understood. As part of a toxicology study, we fed groups of mice three different diets for 10 weeks: marine fish, 58% homogenized Atlantic smelt and herring; freshwater fish, 58% smelt and alewife from the North American Great Lakes, and commercial dry rodent chow. Between 1 and 15 weeks following dietary treatment, 20 of 103 (19.4%) mice unexpectedly developed spontaneous lymphoma. Disease incidence peaked when the mice were 7-8 months old, and was not distributed equally across treatment groups. Mice in the control (30%) and fresh water fish (27.5%) groups had significantly higher incidences of lymphoma than those fed Atlantic fish species (5%). Although our experiment was not originally designed for this purpose, our results indicate that consumption of fat-rich Atlantic smelt and herring protected mice against hematopoietic tumor development.