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BULLETIN OF THE BUREAU OF FISHERIES 
less intermediate in size of the perch and the trout, but overlap somewhat with both 
species. 
At Beaufort the eggs of the three species named often were taken in the same 
towing, assuming of course that the largest ones were trout eggs. The pigfish eggs, 
like those of the gray trout, are very similar to the perch eggs and are scarcely dis- 
tinguishable (although their average size is larger), until the embryos become well 
developed. In the advanced embryonic stages the oil globule in the perch egg acquires 
greenish specks, whereas the oil globule generally remains clear in the pigfish, or at 
most it acquires only a few minute specks. Furthermore, the position of the oil 
globule in relation to the embryo is characteristic. In the perch (also the trout) it 
lies far behind the head, whereas in the pigfish it lies at or near the ventral surface of 
the head. The newly hatched fish, too, may be distinguished by the location of the 
oil globule within the yolk sac, as it retains the approximate position it has in the em- 
bryo, that is, it lies in the posterior part of the yolk sac in the perch (and trout), and 
in the anterior part of the yolk sac or under the head in the pigfish. 
Pearson’s (MS.) measurements, in the absence of descriptions of color marking 
and statements in regard to the position of the oil globule with respect to the embryo, 
suggest that he may have grouped the eggs of the pigfish, the white perch (also known 
as the yellow-tail perch), as well as those of the gray trout, all under C. regalis. All 
three species no doubt spawn in Chesapeake Bay or off the month of the bay during 
the period in which the eggs were taken by Pearson, as Hildebrand and Schroeder 
(1928, pp. 258 and 280) took spawning pigfish during June, and ripe perch during May 
in Chesapeake Bay, and Radcliffe (in Welsh and Breder, 1923, p. 151) took trout eggs 
there during the spring. Since Pearson does not list the eggs of the pigfish and the 
perch (both very common species in Chesapeake Bay), although they most probably 
were present among the trout eggs, lends support to the supposition that they may 
not have been distinguished. 
Too much faith apparently should not be placed in the measurements of eggs, 
unless it is known definitely that the eggs were spawned in water of about even density. 
If preserved eggs are measured, it would seem necessary to use one preservative of 
uniform strength. Delsman (1931, p. 403) has shown that a comparatively large 
difference in size exists in the eggs of one species ( Cybium guttatum), depending upon 
the density of the water in which they are taken. Eggs collected in the mouths of 
rivers where the water was brackish were larger, varying in diameter from 1.24 to 
1.36 millimeters, than those taken in salt water, which had a range in diameter of 
1.05 to 1.26 millimeters. Delsman concludes: 
So we easily came to the conclusion that the size of the egg depends on the salinity of the water, 
increasing or decreasing in proportion to the latter getting lower or higher. The same phenomenon 
has been observed in other pelagic eggs, the eggs of the Baltic Sea fishes, e.g., being bigger than the 
corresponding eggs of the North Sea. 
Kuntz (1914, pp. 4-10), presumably Welsh and Breder (1923, p. 151), and the 
present writers measured live eggs, whereas Pearson measured preserved eggs. The 
present investigators are not aware of data that show how the eggs are affected by 
the commonly used preservatives. Pearson apparently assumes that some shrinkage 
takes place and, therefore, left the eggs “in preservative at least 6 months in order to 
obtain nearly the minimum shrinkage.” However, he does not name the preserva- 
tive, nor the strength at which it was used. The measurements made by Pearson and 
the other investigators, therefore, may not be directly comparable, although in 
general they are in agreement, as already stated. 
