74 BULLETIN OF THE BUREAU OF FISHERIES. 



picture as the salmon proceed up the rivers, one may say, with all due respect to the 

 previous work, that such picture has not yet been given for any species. 



The king salmon of our Pacific waters is an entirely distinct genus from that of the 

 Atlantic salmon. It is decidedly unique in its biological characteristics, as shown in a 

 number of fundamental ways. These characteristics have been enumerated at various 

 times," but three facts of pecuHar importance may again be stated here as most vital 

 to this investigation: 



First, Oncorhynchus tschawytscha is an anadromous fish. 



Second, it fasts completely during its entire journey from the sea through the tidal 

 waters and up the rivers to the spawning grounds. 



Third, Oncorhynchus always dies within a short time after spawning.* It can not, 

 therefore, return to the sea for a second period of feeding. 



These facts, taken in connection with my numerous quantitative chemical deter- 

 minations revealing variations in the percentages of the fats within wide extremes, 

 form the scientific background of interest in this investigation. There are enormous 

 economic interests involved on the Pacific coast in the catching of the king salmon and 

 the conserving of the flesh as food. There is a well-known great variation in the grade 

 of the commercial products derived from this fish. These facts add to the scientific 

 interest in the problem, and emphasize the necessity of a study of the histological distri- 

 bution and utilization of the fats in the king salmon, the largest and finest of all the 

 members of the family of Salmonidae. 



At the time the king salmon leaves the ocean for the fresh water it has reached the 

 crest of the life cycle as regards the amount of fat deposited in its tissue. In the Colum- 

 bia River those salmon caught at the lowest point at the mouth of the river are the fattest 

 of all. The salmon do not feed, i. e., they do not absorb new food materials, during their 

 return passage in fresh water. There is no other adequate storage of food material than 

 this fat. One may, therefore, safely assume with Miescher that the fat is the chief 

 source not only of the fats that go to build up the ovaries but also of the energy liberated 

 in muscular contractions during the migration journey. One may also assume as a 

 working hypothesis that the fat will decrease in amount until the spawning is accom- 

 plished and the death ensues. I have followed the variation in chemical composition in 

 the king salmon muscles, including the amount of fat at the different stages of the spawn- 

 ing migration, work that is represented by unpublished results obtained from chemical 

 analytical determinations, and have also followed the microscopic distribution and varia- 

 tions of the fat in fat-stained muscular tissues. It is the results of this latter work to 

 which attention is called in this paper. 



MATERIAL AND METHODS OF INVESTIGATION. 



The facts presented in this paper concerning the salmon fats have been determined 

 by the microscope."^ The chief reliance has been placed on the special methods for 



a Greene, C. W.: Physiological studies of the chinook salmon. Bulletin of the U. S. Bureau of Fisheries, vol. xxrv, 1904, 

 p. 429-456. 



^ Evermann. B. W.: A preliminary report upon salmon investigations in Idaho in 1894. Bulletin U. S. Fish Commission, 

 vol. XV, 1895 (1896), p. 253. Also, A report upon salmon investigations in the headwaters of the Columbia River in the State 

 of Idaho in 1895. together with notes upon the fishes observed in that State in 1S94 and 1895. ibid., vol. xvl, 1896, p. 184. 



c I wish to express my deep obligation to Mr. Thomas J. Heldt, instructor in anatomy, University of Missouri, and to Mr. 

 George T. Kline, biological artist. University of Missouri, for their valuable assistance in the taking of samples and in the 

 making of the numerous field observations on fresh materials, on the excellence of which much of the detail of this paper rests. 



