30 



ANNALS NEW YORK ACADEMY OF SCIENCES 



Osmotic Pressure or the Blood of an Elasmobranch taken from 



Brackish Water 



The dog-fishes probably migrate. I am informed by Mr. Denyse of the 

 JSTew York Aquarium that the spiny dog-fish, Squalis acanthias, is present 

 in New York waters for a time during the latter part of May and the 

 first part of June, and then disappears until the autumn, when it returns 

 to remain until after the New Year. Observations are lacking during the 

 mid-winter, as no fishing is done at that time, but for a number of weeks 

 after the fishing is begun in the spring there is no sign of this species. 

 Mr. Denyse informs me that the smooth dog-fish has been taken at some 

 distance up the Hudson Eiver. It is very probable then that in their 

 migrations up and down the coast they pass the mouths of rivers in which 

 the water must be brackish, especially in the spring time when the rivers 

 are swollen with the spring freshets. Mr. Denyse has kept a daily record 

 of the temperature and salinity of the water from New York harbor for 

 the period from 1903 to 1911. From the monthly averages of that record, 

 published in the Eeport of the Director of the New York Aquarium 

 ('12 ), I have computed the average monthly specific gravity of the har- 

 bor water for the nine years in question. The results of this calculation 

 are shown in Table XI. 



Table XI. — Average monthly specific gravity of New York harbor icater for 



the years 1903-1911 ^ 



Month 



Specific gravity 



Month 



Specific gravity 



January 



February .... 



March 



April 



May 



1.0139 

 1.0135 

 1.0121 

 1.0100 

 1.0120 

 1.0133 



July 



August 



September . . . 



October 



November . . . 

 December 



1.0148 

 1.0154 

 1.0155 

 1.0148 

 1.0147 

 1.0147 



June 



Although the migration of fishes is usually stated to be due to a search 

 for better food conditions and for the purpose of spawning, there is a 

 possibility that the non-appearance of Squalus in New York waters dur- 

 ing the early spring is due to the dilute condition of the water. The 

 density of the water is lowest during April. A considerable rise is noted 

 in May and June, and it is then that these fishes make their first appear- 

 ance. 



These considerations lead to the question whether the dog-fish is sensi- 



From daily observations made by Mr. W. I. Denyse at the New York Aquarium. 



