THYROID TUMOR IN SALMONOIDS 



By M. C. Marsh 



Tumors of many kinds or types are known among fishes, 

 most of them rare and of little interest to the fish cul- 

 turist, though of importance to the comparative pathol- 

 ogist. Among the members of the salmon family the so- 

 called throat or gill tumor, which is the thyroid tumor, is 

 common in domestication, and of particular interest from 

 several points of view. Somewhat as the general class of 

 tumors includes the cancer, so this thyroid enlargement in 

 fishes has a stage which the cancer pathologists have 

 diagnosed as cancer. Since cancer is the most terrible of 

 the unsolved scourges of the race, and the most baffling 

 of the riddles of pathology, its occurrence in any of the 

 lower animals provides a valuable field for comparative 

 study and experiment. The mere fact that this disease or 

 its underlying stage is common among domesticated fish is 

 sufficient to challenge the attention of all interested in fishes 

 or fish culture. 



A tumor in its literal or broadest and earliest signification 

 means a swelling of any part or tissue of the living 

 organism. As used in pathology it includes those numerous 

 kinds of enlargements which are true new growths or 

 abnormal and more or less unlimited increases of pre- 

 existing normal tissues. Technically tumors include the 

 malignant growths, as carcinoma or cancer and sarcoma, 

 as well as the benign. All are classed together under the 

 one general head because of the quality common to all, of 

 abnormal growth, unchecked by the ordinary physiological 

 limitations. 



The thyroid tumor in fishes is an enlargement of the 

 thyroid gland. This is a small ductless gland with an in- 

 ternal secretion essential to the health of the animal. In 

 the fish it is located beneath the floor of the mouth, or 



