THE HERRING AND ITS ALLIES . 
403 
thoroughly impregnated, and were hatched out with a loss of hardly one 
per cent. 
Shad ready to deposit their spawn seem to prefer waters of a warmer 
temperature than 6o° F. Therefore, when the mature Shad, intent on 
reproduction, leave the hydrothermal area of 6o° F. and ascend the rivers 
into waters of 65° to 70° F. and upwards, they are unaccompanied by the 
half-grown Shad, the latter ceasing to ascend as soon as they encounter 
a temperature of more than 6o° F. In 1882, however, when the tem¬ 
perature of the water was below 60 0 F. for the greater portion of the 
season, the spawning had to take place in water colder than the fish would 
have preferred, and therefore mature and young Shad were found together 
on the spawning grounds. 
The shad-fry, which spend the first six months in our rivers, must of ne¬ 
cessity find their food therein. From examinations made of the stomachs of 
these young fish, they have been found to feed upon certain species of Crus¬ 
tacea and insect larvae, common to the fresh waters of our rivers. During the 
spring of 1882 some young fry, which were hatched out at Central station, 
were confined by Dr. John A. Ryder in a glass aquarium, through which 
the circulation of the water was maintained, and fed with Copepoda, 
obtained in large quantities from the United States carp ponds. In about 
seven days after hatching some of the young fry were' observed to eat, 
and a few days later they were all vigorously engaged in pursuit of food. 
While the ratio of mortality was large, some of the fish survived for six 
weeks, the last specimen having attained a length of considerably more 
than an inch, and a weight many times greater than that at birth. 
From these experiments we deem it altogether probable that under 
natural conditions the Copepoda, which are abundant in the Potomac in 
places frequented by the young Shad, are their natural food during the 
early stages of their existence. 
It is probable that Shad in their early lives vary their food with min¬ 
nows and the young of other species of fish. Indeed, from the stomach 
of a Shad, taken in one of the pounds at Saybrook, I found an undigested 
minnow two or three inches in length. I11 the fresh-water life of the 
mature Shad, the fish do not seem to take food at all. Repeated observa¬ 
tions of the contents of the stomach show no food whatever. Occasionally, 
however, they can be induced to rise to a fly dexterously cast on the water. 
This fact is presumptive evidence that the desire for food, although sub- 
