172 
BULLETIN OF THE BUREAU OF FISHERIES 
fact that these irregularities in form are more constantly present and more emphasized 
at the beginning of the fourth year than during the previous springs. This age is 
determined from the scale, which shows these markings at the beginning of the 
fourth annual zone. The fish then measures from 4^ to 6 inches. It is in specimens 
of this size that ripe gonads have first been found, and Reighard reports that the 
smallest ones seen spawning by him were about 6 inches long. However, other 
factors besides either the sexual cycle, food, or temperature alone must operate to 
cause the variations described each year. Otherwise we would have difficulty in 
accounting for such facts as the varia- 
tion in spacing from May to October 
of the first and second summers. 
A very interesting local variation 
was observed in suckers seined in No- 
vember from a large spring, where they 
probably lived the year round. Their 
scales showed virtually no seasonal vari- 
ations of the sort described as usually 
present. Though sexually mature (6 to 
10 inches), not even the markings so 
pronounced in the fifth and sixth springs 
were noticeable. 3 This fact, taken alone, 
would point to the direct regulative 
effect of an evenly cold temperature. 
Again, the greatest contrasts in spacing 
have been observed in fish from pools 
between falls, where they probably have 
Fig. 55— Detail of the last two annual zones on a scale of a remained all their lives Subject to ex- 
13-inch specimen taken in April J 
tremes of warm and cold water coming 
from the exposed and shallow creeks emptying into the pools. 
ANNUAL GROWTH 
On the basis of the annual zones on the scales we can determine the average 
lengths of specimens at each year of their lives. The following table is a summary 
of the average lengths of specimens showing from one to seven annual zones on the 
scales. Not over a dozen of each age were averaged, and the record is incomplete, 
as the white sucker is known to attain a length of 22 inches. The specimens used 
were taken in the late summer or fall. The first season is therefore but half a year. 
Inches 
First season — — 
Second season 3 
Third season _I 4 
Fourth season 1 4)^-6 
Fifth season 6-8 
Sixth season 8-13J^ 
Seventh season 1 ■_ 13J^-15J^ 
The rapid growth during the sixth and seventh years seems surprising and would 
be interesting to test upon fish confined or tagged and recovered. 
3 Scales from these and other suckers could be separated on sight, even when purposely mixed. 
