101] STUDY OF SOUTHERN WISCONSIN FISHES— CAHN 101 



fertilized in a glass dish at 3:30 o'clock in the afternoon of December 2, 

 the fertilization membranes appearing around the eggs very quickly. 

 At 9 p.m. the eggs were all in the 2-celled stage; at 12 midnight the 8-celled 

 stage was nearly completed, while at 8 a.m. on December 3, the 64-celled 

 stage was beautifully marked. The temperature here ran from 4.5°C to 

 5.5°C. At 3 o'clock that afternoon the cells were too numerous to count, 

 and from then on the eggs were permitted to develop without observation. 

 The exact length of the developmental period has never been worked out. 



THE YOUNG 



I believe that young ciscos are among the least known of all of the 

 Wisconsin fishes. In fact, there is no evidence that anyone other than 

 myself has ever taken them alive in nature, and it took me nine years of 

 search before I finally got three individuals. These were young of the 

 year, taken in Oconomowoc lake on July 20, 1922, in a trammel net set 

 on the bottom in 52 feet of water. They measured 6.25 cm in length, and 

 are the only young-of-the-year that I have ever handled. Much popular 

 misinformation is in circulation in southern Wisconsin concerning the 

 young cisco, as the brook silversides {Labidesthes siceulus) is uniformly 

 considered as the young of Lencichthys artedi. This is due largely to a cer- 

 tain similarity of shape and color, and to the well known lack of discrimin- 

 ate observation on the part of people in general. This mistaken identity 

 works for the good of the silversides, for as the cisco is protected by law, 

 many bait gatherers scrupulously return Labidesthes to the water. 



As the ice forms over the shallow water very soon after the eggs are laid, 

 difficulties in determining the movement of the young after hatching are 

 greatly increased. Upon hatching the young fish seek the deep water, and 

 this occurs prior to the complete breaking up of the ice in the spring, 

 which takes place usually about the first or second week of April. Re- 

 peatedly have I marked the spot where eggs were deposited, only to find 

 them hatched when the breaking of the ice made re-examination possible. 

 That the hatching takes place late in March is suggested by the condition 

 of development of eggs retrieved by chopping through the ice in late 

 February and early March. This would make the developmental period 

 between ten and twelve weeks, probably with considerable variation 

 depending upon the temperature conditions, longer during a long winter, 

 and shorter in the case of an early spring. The young, then, seek the deep 

 water where, because of their small size, they are almost entirely inaccessible 

 for study. There is nothing to indicate that anything of unusual interest 

 takes place during this juvenile condition. 



Through the cooperation of the dozens of fishermen who catch the 

 cisco through the ice during the winter, the writer has had the opportunity 

 of examining hundreds of specimens for size measurements and food habits. 



