CARCINOMA OF THE THYROID IN SALMONOID FISHES. 
431 
Pond 5 in August, 1909, contained lot 2017, consisting of 729 yearling hybrids 
(female brook trout and male landlocked salmon), all clean fish. These were the 
survivors of 1,553 fish of the previous April, all of which were clean at that time. This 
lot was almost immune for two years. Only 1 3 red floors and 2 tumors were produced 
in one year. The next year all of the remaining fish were clean, and finally in 1912 
there were 10 tumored fish among the 220 remaining. 
In pond 6 were placed, in August, 1909, 469 yearling chinook salmon. This pond 
previously contained lot 1994, badly affected hybrid salmon. During the two years 
in which these chinook salmon were kept under observation no visible thyroid process 
was produced. This species (Oncorhynchus tschawytscha) is a Pacific salmon, an 
anadromous marine fish. In no adult marine salmon have we seen thyroid disease. 
Humpback salmon yearlings in troughs of fresh water at the hatchery acquired a heavy 
tumor involvement. 
Ponds 7 and 8 contained in July, 1910, 147 clean yearling rainbow trout (lot 2133). 
No visible tumors have been produced. After one year 3 per cent had red floors and 
after two years only 2 fish of the 31 remaining had the incipient process. 
Pond 9 held, in August, 1909, 97 clean 2-year-old landlocked salmon. They 
remained clean during the first year. In July, 191 1, there were 10 per cent of red floors, 
but no visible tumors. In August, 1912, there were but 32 fish left, of which i had a 
red floor and i a tumor and red floor. 
Pond 10 is the lowermost of the first row of ponds and is almost entirely supplied 
by previously used water. In August, 1909, the 673 clean, 2-year-old landlocked salmon 
remaining after the removal of 219 tumored fish from lot 1950 were placed in this 
pond. The loss was not excessive on this lot. By July, 1911, 7.7 per cent had visible 
tumors while 37 per cent were affected, the fish having reached 4 years of age. Thus 
the tumor fish of this lot recovered under more natural conditions in pond i , while the 
remainder continued to develop tumors under the intensive conditions of pond 10. 
Pond 12 receives 30 gallons per minute of unused brook water only. In August, 
1909, 7 tumored fish were removed from the 2-year-old brook trout of lot 1939 A 
and the 223 clean fish were left in pond 12. In July, 1910, but 80 fish remained, of 
which 5 per cent were affected, including but one tumor. In 1911, 5 per cent had 
tumors and 25 per cent were affected. In 1912 the remaining 58 fish had a slight 
increase in both respects. 
Pond 13 contained cyprinoid fish, which do not, so far as obseiA’^ed, acquire thyroid 
tumors or any notable thyroid changes, and are not considered in the present study. 
Pond 14 contained in August, 1909, 167 clean 2-year-old brook trout remaining after 
the removal of 16 tumored fish from lot 1937. During the next year the thyroid process 
progressed rapidly, 15 per cent acquiring tumors and 31 per cent becoming affected. 
During the next year there was a very definite regressive process, and during the last 
year, the fish reaching 5 years of age, there was again a slight progression. Pond 15 
had similar susceptible fish, the process continuing slowly at first and then more rapidly. 
Ponds 17 and 18 contain Scotch sea trout, which are of especial interest and impor- 
tance. These ponds receive almost entirely previously used brook water, and the 
