GREAT LAKES COREGONIDS 549 



chiefly on Chironomus larvae and pupae. It is probable that its food preferences are 

 similar to those of its relative in Huron. As in Lake Huron, the species is charged 

 with the destruction of trout spawn by virtually every fisherman who is familiar 

 with it, and all these men claim to have seen the trout eggs in the pilot's stomach. 

 Some data on this propensity of the pilot are given on page 552. 



COMMERCIAL VALUE 



As a food fish the pilot is always rated above the herring, but in this respect it 

 does not even approach the whitefish. The flesh has little fat and spoils readily, 

 so that the pilot nets have to be lifted at short intervals. The fish are sold either 

 fresh or salted. 



Prosopium quadrilaterale of Lake Huron 



The pilot of Lake Huron differs in few characters from its relative in Lake Michi- 

 gan. The principal characters capable of numerical expression are compared below: 

 Gill rakers on the first branchial arch: I H/E: 



Michigan, (15) 16-18 (19)." Michigan, (3.9) 4.3-4.6 (5) 



Huron, (15) 16-17 (19) . 85 Huron, (4) 4.2-4.5 (4.9). 



Lateral-line scales: Pv/P: 



Michigan, (84) 87-95 (100). Michigan, (1.8) 1.9-2.2 (2 3) 



Huron, (80) 84-91 (95). Huron, (1.5) 1.8-2 (2.3). 



L/H: Av/V: 



Michigan, (4.9) 5.2-5.4 (5.6). Michigan, 2.1-2.3 (2.5). 



Huron, (4.5) 4.8-5.1 (5.3). Huron, (1.8) 2.1-2.2 (2.4). 



It appears, thus, that Huron specimens tend to have a proportionally larger 

 head, somewhat longer paired fins, and slightly fewer lateral-line scales. Of course 

 data are required from many more specimens from both lakes in order to establish 

 the course of the distribution curve for any characters. 



The color in life is as in the Michigan form, except that, as a rule, specimens 

 are more heavily pigmented. This character, of course, is most in evidence in alco- 

 holic material. The pigment below the lateral line, besides being more abundant 

 extends often to the belly. The paired fins often are pigmented distinctly and 

 frequently there are dots on the anal. 



Pearl organs are well developed on males during the breeding season and at 

 least faintly indicated on some females. I have collected no specimens during or 

 immediately previous to the spawning period, and therefore I do not know to what 

 extent nuptial buttons are developed on the two sexes. Pearls were beginning to 

 appear on males taken at the Greater Duck Island on October 18, 1919, were present 

 on males and a few females taken at Wiarton, Ontario, on November 5 1917 a t 

 Kagawong, Ontario, on November 10, 1917, at Alpena, Mich., on November 'l5 

 1919, and in Au Sable River, Mich, in November, 1924. None of these fish were 

 ripe. The maximum development of pearls that I have seem for the species is exhib 

 ited by specimen No. 1087 from Wiarton. On this fish they are present on the 

 lateral line and on each scale of the first four rows above and below it. On the fifth 



* Figures for Michigan, excepting those for scales, are based on an examination of 34 specimens ranging in length from 200 to 

 419 millimeters. Figures for scales are given for 65 specimens. ■ 200 t0 



» ! Figures for Huron are based on an examination of 72 specimens ranging in length from 200 to 393 millimeters. 



