428 BULLETIN OF THE BUREAU OF FISHERIES. 



group of wooden troughs which the records showed had been previously occupied by 

 the fish that were now affected in the ponds. In October, 1909, these troughs were occu- 

 pied by small fish hatched the preceding spring, and from one of the troughs a small 

 brook trout, a so-called fingerling, was found dead and proved on examination to have a 

 protruding visible tumor in the* thyroid region. (See fig. 73.) On microscopic examina- 

 tion this was found to be tubulo-alveolar solid carcinoma, infiltrating the surrounding 

 structures. (See fig. 64.) 



These, in the main, are the facts which were impressed upon us by the undisturbed 

 conditions at Craig Brook. The observations of the following summers were carried 

 out on a more extensive basis. 



CRAIG BROOK STATION: CONDITIONS DURING THREE YEARS. 



The Craig Brook fish cultural station (fig. 77) of the United States Bureau of 

 Fisheries is located on Lake Alamoosook about i mile from East Orland, Hancock Co., 

 Me. It is but a few feet above tidewater. The station was established in 1879 for 

 the artificial propagation of trout and salmon, though Atlantic salmon eggs were first 

 hatched there in 1871-2. It is well provided with troughs in hatchery buildings for 

 the incubation and hatching of eggs, with troughs out of doors for the rearing of young 

 fish, and with earthen ponds for holding older fish and adults. Craig Pond drains 

 into Lake Alamoosook through Craig Brook, the whole flow of which is intercepted for 

 fish-cultural purposes. A small quantity of spring water is also available for the station 

 supply. 



Fish culture at Craig Brook has been chiefly concerned with brook and rainbow 

 trout, the Scotch sea trout, landlocked salmon, and with hybrid trout and hybrids of 

 some Pacific salmon. Investigations of thyroid disease among the fish were first made 

 in 1909, as above stated, and have been continued more or less to date, especially during 

 the summer months. Thyroid carcinoma was immediately found endemic at the 

 station, and affected every salmonoid species or hybrid except the Scotch sea trout, 

 which is almost immune, and the chinook salmon. 



The system of outside ponds holding adult fish at Craig Brook station is shown in 

 figure 78 (p. 429), and has been already referred to. A more exact study of the 

 water supply shows that, with two "exceptions, these 19 ponds receive brook water and 

 in part discharge into each other from the upper to the lower. Pond i , however, re- 

 ceives only spring water, which is discharged into pond 1 1 and thence drains independ- 

 ently of all others. The rest of the ponds are each supplied in part with fresh brook 

 water and in part with this water after it has flowed through preceding ponds in the 

 series. The ponds are entirely of earth and some have small quantities of higher 

 plant life, besides harboring abundant growths of filamentous green algae during the 

 summer months. Ponds i and n are best supplied with vegetation. (Fig. 80.) 



