THE FEEDING OF TROUT IN RELATION 

 TO THYROID TUMOR 



By M. C. Marsh, State Institute for the Study of 

 Malignant Disease, Buffalo, N. Y. 



The enlargement of the thyroid gland in various mem- 

 bers of the salmon family is familiar to most of you 

 either from the fish itself or various publications. This 

 enlargement is of the most various degree and produces 

 often a distinct, palpable swelling, or thyroid tumor. It 

 is a disease process whose various stages have been held 

 to include goiter and cancer, though we now consider 

 the whole process as really one disease. A more detailed 

 account is unnecessary here, extended reports having al- 

 ready been made. Some recent observations make it 

 desirable to offer to this society some brief remarks on 

 the relation of food to this growth. 



The tumor occurs in both wild and domesticated trout, 

 but is everywhere rare in the former and very common 

 among the latter in this country. It has been supposed 

 that the raw meat foods so largely fed in American 

 hatcheries were an important factor in causing the tu- 

 mor growth. These foods, consisting of liver, heart, 

 lungs and other organs of various domestic animals, 

 often mixed with mush made from flour, make a diet to 

 which trout are quite unaccustomed in the wild state but 

 upon which domesticated trout have lived for many gen- 

 erations. However unnatural such foods, trout are able 

 to grow, fatten and reproduce by their use. This feed- 

 ing of mammalian flesh, however it may predispose to 

 and accentuate the disease in hatcheries, is not necessary 

 to the growth of thyroid tumors. This was inferred 

 from their occasional occurrence in wild fish, especially 

 in a whitefish, which is a species whose natural food is 

 plankton. Now there is important additional proof of 

 this. In the aquarium at Naples, Italy, five among a few 

 hundred sea bass dying in the tanks have developed thy- 

 roid tumors. They were fed only upon fresh sea fish, 



