96 
BULLETIN OP THE BUREAU OF FISHERIES 
The fish examined by Bigelow and Welsh were taken far enough out in the Gulf of Maine to 
be removed from the influence of bay or river, and it is probable that their stomach contents show 
more truly than any of the other records given in the foregoing list the sort of food eaten by the 
shad at sea. These stomach examinations, therefore, justify Bigelow and Welsh’s statement that 
the shad is primarily a plankton feeder. 
The fact that adult shad in the sea are known to feed partly on mysid shrimps (bottom dwellers) , 
on bottom-dwelling amphipods, etc., and on algse is of considerable importance, as it suggests 
that part of a shad’s life, perhaps a considerable part, is spent near the bottom of the sea. • This 
may explain why so few shad are caught in the open sea south of Cape Cod. In the Gulf of Maine, 
however, large catches of shad are often made near the surface with purse seines, and it may be 
that in this region an abundant supply of food in the upper stratum of water lures the fish within 
reach of the nets. A change in the diet of the shad with age is suggested by the presence of numerous 
long cceca connected with the intestine near the stomach, which are very small or wanting in the 
young. 
The life history of the shad is not well understood. It enters bays and rivers of the Atlantic 
coast of the United States in the spring, reaching the southern streams much earlier than the northern 
ones, and it ascends to fresh water for the purpose of spawning. The shad may spawn anywhere, 
but it appears to prefer shallow flats in rivers near the mouths of creeks. The fish are paired, 
swimming side by side, while spawning. The eggs are cast loose in the water, quickly sinking to 
the bottom, where many doubtlessly find unfavorable ground and fail to hatch. 
The shad enters Chesapeake Bay in March, the date of arrival varying from year to year, 
and, with the exception of a few stragglers, they are gone again by the 1st of June. In 1921 a 
few shad were taken in pound nets in Chesapeake Bay throughout June and July and again during 
the latter part of November and early in December. These small and rather unusual fall runs, 
which occur only occasionally, naturally excite considerable interest. Whether such shad have 
remained in the inshore waters since spring, or whether they represent a new run from the sea is 
not definitely known; but inasmuch as extensive collecting in the inshore waters during the summer 
months has never brought an adult shad to light, it appears more reasonable to believe that they 
come from the sea. A female 17)4 inches long, taken on December 5, 1921, was preserved and 
critically examined in the laboratory and found to agree in all respects with the individuals of the 
spring run, except that it was smaller than the average size of the spring run of roe shad. This 
particular shad was full of eggs, which evidently were nearly mature. Whether or not the shad 
that constitute the fall runs usually are gravid is not known to the authors, but if this were the case 
the reason for their migration toward fresh water evidently would be the same as for the spring 
run — viz, for the purpose of reproduction. When the shad first arrive the males, or “buck shad,” 
are greatly in the majority, but later in the season the females, or “roe shad,” are the more numerous. 
Spawning takes place soon after the fish reach fresh water. The eggs are relatively large after 
impregnation, measuring about 3 millimeters ()4 inch) in diameter. The average number of eggs 
produced by a female, according to Smith (1907, p. 127), is from 25,000 to 30,000, but there are 
records of over 100,000 and in one case of 156,000 eggs having been taken from one fish. The 
period of incubation varies from six days and four hours in an average water temperature of 57.2° F. 
to a little less than three days in an average temperature of 74° F. (Ryder, 1884, p. 796). It is 
not considered an advantage, however, either to retard or to hasten hatching unduly, as a very long 
period of incubation may result in a proportionately smaller hatch and a very short incubation 
period yields weak fry. The average hatching period at temperatures that prevail during normal 
shad seasons varies from about six to ten days. 
Although shad usually deposit their spawn in fresh water, recent studies by Leim (1924, p. 264) 
in the Bay of Fundy have shown that “the optimum conditions for the development of the eggs 
and larvffi up to the end of the period of yolk-sac absorption were a temperature of about 17° C., 
a salinity of about 7.5 per mille, and darkness.” This is a most important finding, as virtually all 
shad hatching heretofore has been done in fresh water and largely in comparatively bright light. 
Leach (1925, p. 485) reared shad successfully in a fresh-water pond at Washington, D. C., and 
in October, at the age of 5 months, transferred them to brackish-water aquaria (increasing the 
density of the water gradually from 1.005 to 1.018), in which they continued to thrive. Others 
of the same lot, transferred to fresh-water aquaria, died within three days. 
