WHITE SUCKER 
169 
The scales have a smooth edge except for a slight indentation of the margin at 
the end of each radius. I have found that this is not true of scales taken in the late 
winter and early spring, however, in which the edge is straight. 
Attempts to photograph scales were not successful, but drawings made carefully 
to scale are presented in illustration of certain features of scale growth. 
Scale formation begins when the fry are somewhat less than 22 millimeters in 
length (40 days from hatching). However, none could be removed in specimens 
under this length, even by scraping the surface. Those first obtained measure one- 
third of a millimeter in diameter, and it is probable that they represent scales from 
the region of the lateral line, for in fishes generally it is known that the scales 
first appear in this region. By the time the fry are 25 millimeters long scales seem 
to be everywhere present. While the first showed but three circuli, on an average 
four are now present. It is also noticeable that the pigment in the dermis follows 
the edges of the scales, forming a cross-hatched pattern. This pattern is limited at 
first to the sides of the fish in the first and las* 
third of the body. When 28 millimeters lon^ 
the scales show five circuli, there being a striking 
uniformity in this respect. The pigment pattern 
mentioned above now occurs over the entire 
scale-bearing portion of the fish. 
By autumn of the first season the scales 
average about 10 circuli each. (Fig. 50.) This 
figure is important, in that we know definitely 
the time in which they have formed this number. 
One can detect, even at this time, that the 
circuli formed during the summer and fall are 
more closely crowded than those of the spring. 
It is in the very early spring that sucker scales 
show the widest spacing of circuli. In some 
species, such as the carp, this is said to be true 
of those formed in midsummer. 
If we now take the scale of a larger fish, say 5 or 6 inches long, we find that it is 
correspondingly larger and shows many more circuli. These are seen to fall into 
groups or zones, each zone containing a band of widely spaced circuli followed by 
another band in which the circuli are more closely crowded. 
In other species these zones of circuli are known to indicate the annual growth 
of the scale. They are spoken of as “annuli,” and by counting them the age is 
determined. The question arises as to the evidence that they represent such annual 
growth in this species. 
By frequent collecting throughout the summer there is left no doubt but that 
fingerlings 1 )/£ inches in length are but one season old. Their scales show but one 
zone of circuli, widely spaced at first but becoming narrowly spaced in the fall. 
This is, then, a true annual zone. The fact that in later years zones of about the 
same width and containing about the same number of circuli are present, but in 
greater numbers, points to the conclusion that they are repetitions of the process 
a snArimpn 40 milliTnptp.rs in lpnerfh 
