ON SOME QUANTITATIVE 



PHYSIOLOGICAL CHANGES IN THE 



PACIFIC SALMON DURING THE RUN TO 



THE SPAWNING GROUNDS 



By Prof. C. W. Greene, 



From the Department of Physiology and Pharmacology, 



Laboratory of Physiology, University of Missouri. 



Among the anadromous fishes, the various species of 

 Salmonoids are probably the largest and most important 

 from an economic point of view. It is now well known 

 (Evermann), that the Pacific salmon of the different 

 species of the genus, Oncorhychus, after they reach ma- 

 turity in the sea and make the run up the rivers to the 

 spawning grounds in the cold fresh-water streams, in- 

 variably die after spawning. The Atlantic salmon, 

 Salmo salar, and the Pacific steelhead, Salmo gairdneri, 

 are supposed after spawning to return to the sea again 

 for another period of feeding and development. 



It is further well proven by the researches of the 

 United States Bureau of Fisheries that the species of 

 Oncorhynchus take no food during the run to the spawn- 

 ing grounds. The king salmon apparently ceases feed- 

 ing upon entering the brackish waters in the region of 

 the mouths of the rivers, and the long run against swift 

 current and mountain torrents, amounting in the case of 

 the Columbia River and its tributaries to as much as 700 

 to 1,000 miles, is made absolutely without food. 



During my work I have found that many, if not the 

 majority, of the individuals of the king salmon enter 

 fresh water (at least in the Sacramento and the Colum- 

 bia River basins) at a period when their reproductive 

 organs are relatively immature. During the run from 

 the mouths of the rivers to the spawning streams and 

 the sojourn immediately following, the greater portion 

 of the mass of the reproductive organs is developed. The 

 two principal facts, namely (1), the expenditure of the 

 large amount of energy without external food, and (2), 



