448 



BULLETIN OF THE BUREAU OF FISHERIES. 



Table X. — Depression of tin freezing point of blood from salmon tah n in th main channel of Suisun Bay 

 at the head of brackish water of the Sun Francisco Una region. 



The mean depression in these seven examples is —0.737° C, a figure which 

 (litters from the mean of the sea salmon by 0.025 c C. In making the run from salt 

 water to the head of brackish water there is therefore a small fall in the osmotic 

 tension of the blood. 



In the meantime the salmon have ceased to feed. The stomachs are empty save 

 for a thick mass of tough mucous, but no obvious changes have occurred in the gross 

 structure of the alimentary canal. It is unfortunate that there is no definite infor- 

 mation as to the time consumed by the fish in adapting itself to the change from salt 

 to fresh water. It has not yet been demonstrated whether the run is direct and 

 continuous or more slow and gradual. The most plausible explanation of the 

 directive influences determining the rapidity with which salmon make the journey 

 through lower tide water is given by Kutter," though he ventures no conclusion as 

 to the rapidity with which the passage through lower tide water is made. He has 

 determined that the progress through upper tide water is comparatively rapid, the 

 salmon making the journey from Vallejo to Sacramento in about four days. There 

 is a belief current among the fishermen at Black Diamond that salmon spend consid- 

 erable time on the Flats along the upper bay. and the muddy condition of the skin 

 and gills of fish caught in this region would to some degree bear out this view. 



Table X shows that a fall of the osmotic pressure of the blood has already begun 

 by the time the fish have reached upper tide water, enough to depress the freezing 

 point by — 0.025 c C. 



THE CONDITION OF THE BLOOD IN SALMON ON THE SPAWNING BEDS. 



Salmon make the run from upper tide water to the spawning grounds at a 

 comparatively rapid rate. Rutter* found that three specimens branded in the lower 

 river at Rio Vista made the run, a distance of about 300 miles, in 65 days in two 

 cases and in (31 days in one case. Rutter states, further, that the average duration 

 of the spring run is six weeks, but that the fish arrive on the spawning beds from 

 two to six weeks before spawning. From these observations it will appear that 

 tlie spring run of salmon at spawning time have been in fresh water from eight to 

 twelve weeks. I have made a large number of determinations on the blood of 

 salmon of this ela>^ taken from the spawning beds at the United States fish hatchery 

 at Baird, Cal., the results of which are given in Table XI. 



a Rutter, Popular Science Monthly, July, 1902, p. 207. 



Mbid., p. 209. 



