394 



BULLETIN OF THE BUREAU OF FISHERIES 



lowest, and the fishermen move their nets in and out to follow them. The time of 

 spawning is said also to be affected by climatic conditions and regularly varies about 

 two weeks. The fish, as a rule, congregate between the middle of October and the 

 first of November and remain on the grounds about a month. In 1920 spawning was 

 later than usual. Out of Milwaukee, on November 15 in 28 to 35 fathoms (record 12), 

 and out of Michigan City, Ind., on November 19 in 18 and 28 to 32 fatboms (records 

 18 and 19), virtually all the females were still hard. The males were pearled and 

 exuded milt on pressure. It is notewortby that the lift on November 19 in 18 fathoms 

 had 93 per cent zenithicus, while the lift made in 28 to 32 fathoms 7 miles farther out 

 on the same course had only 15 per cent. Furthermore, 87 per cent of the fish 

 recorded under record 18 were males, and about the same percentage of the fish 

 recorded under record 12 were females. These observations may indicate that the 

 males may move first to the spawning grounds in shallow water, as is known to be 

 the case in some other coregonids. 



Leucichthys zenithicus of Lake Huron 



Zenithicus in Lake Huron likewise seldom grows larger than 300 millimeters, and 

 as nets of 2%-inch mesh are the smallest used for chubs it is one of the smallest of the 

 chubs commonly taken. In body shape and most other systematic characters the form 

 of Lake Huron closely resembles the typical form. The body, however, is wider on 

 the average. The chief systematic characters are compared in detail in Tables 6 to 

 11, and are summarized below: 



H/M: 



Superior, (2.1) 2.3-2.5 (2.7). 

 Huron, (2.3) 2.4-2.6 (2.7). 



H/S: 



Superior, (3.1) 3.3-3.6 (4). 

 Huron, (3.2) 3.4-3.7 (4). 

 Pv/P: 



Superior, (1.3) 1.6-2 (2.4). 

 Huron, (1.6) 1.9-2.1 (2.3). 

 Av/V: 



Superior, (1) 1.3-1.6 (1.9). 

 Huron, (1.2) 1.5-1.6 (1.8). 



Gill rakers on the first branchial arch: 



Superior, (32) 39-43 (46) 



Huron, (34) 37-40 (44) .« 

 Lateral-line scales: 



Superior, (69) 74-84 (90). 



Huron, (70) 72-82 (88). 

 L/H: 



Superior, (3.6) 3.8-4.1 (4.4). 

 Huron, (3.9) 4.1-4.3 (4.5). 

 H/E: 



Superior, (3.9) 4.2-4.6 (5.1). 

 Huron, (3.9) 4.2-4.6 (5.2). 



These data indicate that the Huron form has, on the average, slightly fewer 

 gill rakers on the first branchial arch, a shorter head, and perhaps a somewhat shorter 

 snout, maxillary, and paired fins than the typical form. Furthermore, while in Lake 

 Superior zenithicus almost always has pigment on the maxillary, 19 out of 116 indi- 

 viduals examined have no pigment on the maxillary but a little on the jugal. The 

 mandible also is less often equal to or longer than the upper jaw. The Michigan form 

 differs from the typical form in virtually the same characters, and the variation is in 

 the same direction. 



The color of living specimens is not different from that of the typical form. 

 Preserved specimens from which all color has vanished show less pigment on the pec- 



*> Figures for Lake Superior for gill rakers are given for 883 specimens, those for scales for 956. All others are given for 787 spec- 

 imens, ranging in length from 200 to 332 millimeters. 



a These and other figures for Lake Huron, except those for lateral-line scales, which are given for 166 specimens, are based on an 

 examination of 91 specimens 200 to 318 millimeters in length. 



