CARCINOMA OF THE THYROID IN SA^MONOID FISHES. 413 



inches in length and in its rather emaciated condition weighed 4 pounds. A salmon of 

 this length in health should weigh 6 to 8 pounds. A large thyroid tumor involved the 

 whole gill region, vegetating in the floor of the mouth and presenting on the ventral 

 surface several cystic lobes which kept the gills and gill covers well distended. (Fig. 72.) 



Sebago Lake is located in the southwestern part of Maine. It has an area of about 

 45 square miles and a general depth of 316 feet. It has but few shoal places, the depth 

 of water often reaching close to the shores, which are for the most part rocky, save in 

 a few shallow coves. The lake has little aquatic vegetation; the water is regarded 

 as unquestionably pure and is the source of supply for the city of Portland. While the 

 fish had been living in a wild state for two or three years, it was originally planted from 

 a fish hatchery, where it may have contracted the disease. Microscopic inspection 

 of this tumor (see fig. 75) shows it to be almost entirely of the alveolar type, showing 

 at the center areas of cystic colloid degeneration. 



These four tumor-bearing fish were living under wild natural conditions when 

 taken. All can be related more or less remotely to fish culture. They were taken from 

 waters in inhabited regions, in which fish culture has been practiced for vears, and these 

 waters had frequently received the products of hatcheries. The trout inhabited a stocked 

 stream, and was possibly the product of a hatchery and fed artificially, or was descended 

 from fish so treated. The landlocked salmon was probably planted from a hatchery. No 

 whitefish are fed artificially nor reared to maturity in domestication. The product of 

 their artificial propagation is planted soon after hatching. The most that may be said, 

 therefore, as far as the relation of this tumor-bearing whitefish to domestication is con- 

 cerned, is that it may have been artificially hatched, planted before feeding, and was 

 living in a large lake which received the drainage from a large trout hatchery and breed- 

 ing establishment at which the thyroid disease was endemic and epidemic. It was taken 

 within 5 miles of the point of entry of this drainage inflow. 



In one of the small lakes of the Adirondack Mountains of New York, which have 

 been stocked with trout from hatcheries, anglers occasionally report the taking of fish 

 with visible tumors at the throat. 



In Europe Hofer (1904, p. 194) reports the disease in wild lake trout (Truita locus- 

 iris) living in the Mondsee. Dr. Plehn informs us that occasionally trout with thyroid 

 tumors and living under wild conditions in the streams of Bavaria are sent to the 

 Bavarian Fisheries Biological Station for examination. 



OCCURRENCE AND COURSE OF THE DISEASE UNDER DOMESTICATION 



DISTRIBUTION OF THE DISEASE IN UNITED STATES HATCHERIES. 



The thyroid tumor among fishes is undoubtedly of wide distribution. We believe 

 it occurs almost universally where trout are made the subject of artificial propagation 

 and rearing under the ordinary conditions of fish culture in the United States. A 

 complete canvass of all the trout-breeding establishments in the country has not yet 

 been made, but such an investigation would beyond question indicate the distribution 

 of the disease as coextensive with trout culture. The following list gives the places 



