CHEMICAL FACTORS AFFECTING THE MIGRA- 

 TORY MOVEMENTS OF THE PACIFIC 



SALMON 



By EDWIN B. POWERS 



DEPARTMENT OF ZOOLOGY, UNIVERSITY OF TENNESSEE, KNOXVILLE, TENN. 



Much excellent and necessary work has 

 been done toward the solution of the prob- 

 lem of the migration of the salmon since the 

 beginning of the studies of their migration 

 routes in 1922. The systematic studies of 

 the scales of salmon have added much 

 important information. 



Certain of these earlier discussions have 

 approached the subject from the point of 

 view that the salmon returns to the parent 

 stream for the simple reason that it was the 

 stream from which it originated. In recent 

 years some doubt as to so simple an expla- 

 nation has arisen in certain quarters. 



Barnes (1937) in his Textbook of Gen- 

 eral Physiology, page 452, states, "If only 

 a millionth of the time and money lavished 

 on the investigation of endocrines of mam- 

 mals were spent on further studies of the 

 hormones of invertebrates, we might begin 

 to have some realization of the hidden 

 powers of chemical regulation throughout 

 the living world." The author will accept 

 Barnes' statement and look to the more 

 recent advances in mammalian physiology 

 for physical and chemical receptors, and 

 see how they are applicable to the problem 

 of salmon migration. 



In certain places, namely the aortic arch 

 and the carotid sinus, the blood vessels of 

 mammals have receptors sensitive to pres- 

 sure and to certain chemical substances, 

 such as oxygen and carbon dioxide tensions. 

 This has been shown by various investiga- 

 tors, Cyon and Ludwig (1866) for pressure 

 in the aortic arch, Herring (1924) for pres- 

 sure in the carotid sinus, J. F. and C. Hey- 

 mans (1927) for respiratory gases in the 

 aortic arch, Heymans and Bouckaert (1930) 

 and Bouckaert and Heymans ( 1933 ) for all 

 these and for respiratory gases in the ca- 

 rotid sinus. Later authors (Schmidt, 1932; 



Bronk and Stella, 1932 and 1935 ; Gemmill 

 and Reeves, 1933; Samaan and Stella, 

 1935 ; Smyth, 1937 ; Comroe and Schmidt, 

 1937; and Boyd, 1937) have added many 

 details. 



The chemical receptors in mammals are 

 sensitive to oxygen (anoxia) and carbon 

 dioxide tensions of the blood and to certain 

 other chemicals. Bard (1938) impressed 

 by such an unusual position for a receptor 

 for respiratory reflex, states, "It is remark- 

 able that this should be the case, since the 

 corresponding defense against excess CO2 

 or acid resides almost entirely in the respi- 

 ratory centers and does not depend to any 

 great extent on reflexes. There is a possible 

 explanation for this in the embryological 

 development of the carotid sinuses, carotid 

 bodies, and aorta, and though it is purely 

 hypothetical it serves at least to make com- 

 prehensible an otherwise inexplicable situ- 

 ation ... in aquatic vertebrates ... it is 

 reasonable to suppose that a reflex mecha- 

 nism to protect against noxious chemical 

 agents could function to best advantage in 

 those parts in which the respiratory ex- 

 change takes place with the external en- 

 vironment, and those parts are the gills. 

 . . . Thus we can find a reasonable expla- 

 nation for the peculiar sensitivity of the 

 carotids and aorta to chemical agents, but 

 what of the respiratory reflexes aroused by 

 changes of pressure in these regions ? These 

 also become understandable as another sur- 

 vival of a coordinating mechanism which 

 was of obvious importance in the aquatic 

 vertebrate but which has lost its primitive 

 significance in the air-breathing adult." 



The biologist of the lower vertebrates 

 does not have to reason by analogy. Car- 

 diac responses have been obtained from 

 pressure on the branchial vessels of Squalus 



72 



