MIGRATION OF SALMON IN COLUMBIA RIVFR. 
T 37 
weight of the fish, I regard this particular aluminum button as almost ideally light 
and strong and conspicuous for use in tagging salmon in fresh water. It is probably 
not visible to the fish that wears it, so can not frighten him, and the possible effects on 
other individuals are of little importance. As for the “tin can” comparison, this point 
makes a very good joke, but has no basis in fact. I have marked numerous salmon on 
the spawning grounds and find that the marked fish come and go with the unmarked 
fish without any disturbing behavior to distinguish them from the other fish of the 
schools. 
For sea-run fish, where the sojourn in salt water lasts for a year or more, aluminum 
will not do. Salt water corrodes aluminum and the disk will probably drop off within 
a year. The corroding property of aluminum in salt water is, however, very valuable 
as an accessory check on salmon that are making the journey through tide water. (See 
figs. 3 and 4.) The degree of corrosion of the aluminum button indicates the relative 
immersion in salt water, although from this fact alone one can not distinguish between 
the corrosion due to a relatively short immersion in concentrated and that produced by 
a longer immersion in more dilute sea water. 
LITTLE INJURY TO FISH IN HANDLING. 
The necessary physical injury to salmon while marking them by the methods used 
in this test are two, or at most three. The first of these is the degree of asphyxiation 
produced by the handling of fish out of water. The second injury is that of cutting the 
7 mm. hole through the caudal fin. The third is the physical effects of the handling. 
By asphyxiation is meant the condition which results from the inability of the 
salmon to secure the usual quantity of oxygen and to get rid of the carbon dioxide 
rapidly enough. With fishes this exchange of oxygen and carbon dioxide takes place 
between the blood in the gills and the water flowing through the mouth and over the 
gills, the oxygen being absorbed from the water into the gills and the carbon dioxide 
exchanged at the same time passing in the opposite direction. If a fish is taken from 
the water and air is allowed to pass freely over the gills, the conditions for the gaseous 
interchange between the air and the blood through the gills is for a time as good, or 
even better, than with water. The trouble comes when the gill covers are tightly closed 
down and when the gill filaments, no longer supported by water, adhere together in a 
mass. These conditions sharply reduce the respiratory efficiency, and asphyxiation 
results. This is slight at first, but is more intense and more rapidly developed later. 
One who gives attention to the fact can not but be impressed by the degree with which 
salmon withstand asphyxiation and the ease with which asphyxiation can be overcome 
b) r artificial respiration. In the above experiments only two salmon required the arti- 
ficial respiration. One of these was a fish weakened by old injuries that were quite 
severe. I do not consider ordinary mild asphyxiation of any particular injury to the 
fish unless it be so pronounced that the irritability of the respiratory center in the 
medulla is lowered enough to stop completely all respiratory movements. 
The injury to the fish from cutting the small hole in the tail for the button is very 
trifling indeed. This cut is for the fish about like making a pin prick in the skin of the 
