328 BULLETIN OF THE BUREAU OF FISHERIES. 
ber 30, same place, 38 females, 2 males; January 4, 1917, 15 m., 5 females, 3 males; 
January 6, same place, 9 females, 7 males; January 8, same place, 34 females, 7 males; 
January 25, 18 m., 28 females, 10 males. These facts indicate that the females feed 
more actively during the winter or that they exceed the males in numbers in the deeper 
parts of the lake. 
The egg string deposited by a perch which had been kept for several months in a 
running-water aquarium is shown in Plate LXXXIII, figure 2. This contained 2,650 
eggs and was deposited on May 1, 1916, when the water temperature was 12° C. A 
string was also laid by another individual in the same aquarium on April 18. Forbes 
and Richardson (1908) mention a string recorded in one of the laboratories of this 
Bureau which measured 88 inches in length and weighed 41 ounces after the water 
had been drained from it. The strings swell very rapidly and harden somewhat after 
leaving the body of the female. They are often thrown over stones, plants, or other 
objects in the water. Gorham (1912) states that they may be attached to willow roots. 
The same authority says that eggs hatch in 8 to 10 days and that the small fry hide 
in nooks alongshore until they appear in schools as fingerlings. Hankinson (1908) 
and Reighard (1915) mention seeing schools of small perch in shallow water, and the 
latter notes that there may be small fishes of other species with them. On August 23, 
1916, a school of about a thousand young perch was observed near our dock just north 
of the University of Wisconsin, and it remained in that locality for over a week. 
Meek (1916, p. 290) says of the European perch: ‘‘The larva measures about 
5 mm. when hatched, and in the course of a year the young attains a length of 6 cm., 
and in two years about 13 cm.’’ We have already noted that perch hatched in the 
spring of 1916 in Lake Mendota had attained by August 30 a length of 68 mm., without 
the tail fin, and that perch less than 130 mm. long were sexually mature (Table 25). 
MIGRATIONS. 
The perch in lakes frequent various localities at different times. In general, 
migrations are correlated with the changes accompanying the rhythmical sequence of 
day and night or with those associated with seasonal succession. In order to secure 
data on the numbers of perch at different depths, fishing was carried on simultaneously 
at various levels. The catch per hour in a gill net gives a fair idea of the number of 
perch present, but rather wide seasonal variations are to be expected. Fishes will 
not be captured unless they are moving, and the lesser activity accompanying lower 
temperatures will cause smaller catches. Another means the authors have used for 
judging the number of fishes present in any locality is by the catch per hour with hook 
and line. During stormy weather the number of perch secured in Lake Wingra from a 
drifting rowboat with hook and line often exceeded that taken in gill nets, probably 
because the shallowness of the lake made it inexpedient for the fishes to move about 
much in windy weather. Neither gill nets nor hooks give accurate data as to the actual 
numbers present. However, they do give information which is of value for judging 
comparative numbers when they are used simultaneously at various depths. 
An examination of Tables 2 to 5 and 27 shows several points of interest in regard 
to the abundance of fishes at various seasons, and it is possible to make a number of 
generalizations from the data presented. In Lake Mendota the course of the annual 
migration is pretty definite. In the winter most of the perch are in deep water. As 
soon as the lake is free from ice there is a migration inshore for spawning, but the perch 
