GREAT LAKES COREGONIDS 



427 



COMPARISONS a ' 



The bluefin can be confused only with zenithicus. A discussion of the differences 

 between these species may be found on page 380. An account of the differences 

 between nigripinnis and reigJiardi is given on page 411. 



Only small examples can be confused with hoiji and Tciyi, as the latter do not 

 grow large. There are too few nigripinnis of a size comparable with these species 

 for contrasting of characters affected by growth. Small nigripinnis may be distin- 

 guished from both by the shorter mandible (which seldom is distinctly superior in this 

 form), the thicker belly walls, and the more decurved dorsal margin of the pectorals. 

 They may be separated further from hoyi by the more numerous lateral-line scales, 

 which in nigripinnis number (73) 79-86 (91), with 87 per cent more than 78, and in 

 hoyi (65) 69-78 (84), with 7 per cent more than 78; by the smaller average number 

 of gill rakers on the first branchial arch; the greater average number«of scale rows; 

 and by the less elliptical body outline, as viewed from the side. The paired fins of 

 small nigripinnis probably will be found to average considerably shorter than those 

 of Tciyi. 



From artedi, nigripinnis usually is separable by its softer, more oily flesh; the 

 body shape, which is ovate, as seen from the side, as compared with the elongate 

 elliptical form in artedi; its fewer gill rakers on the first branchial arch; and by its 

 longer paired fins, head, and maxillary. Some of these characters are compared fully 

 below : 



Gill rakers on the first branchial arch: 



artedi, (41) 45-48 (53), with 87 per cent more than 44. 



nigripinnis, (36) 38-42 (48) , with 2 per cent more than 44. 

 L/H: 



artedi, (4.1) 4.3-4.6 (5.1), with 80 per cent more than 4.3. 

 nigripinnis, (3.7) 3.9-4.2 (4.4), with 2 per cent more than 4.3. 

 H/M: 



artedi, (2.5) 2.7-3 (3.1), with 70 per cent more than 2.7. 

 nigripinnis, (2.3) 2.5-2.7 (2.8), with 3 per cent more than 2.7. 

 Pv/P: 



artedi, (1.7) 2-2.2 (2.8), with 84 per cent more than 1.9. 

 nigripinnis, (1.4) 1.6-1.8 (2.2), with 5 per cent more than 1.9. 

 Av/V: 



artedi, (1.3) 1.6-1.8 (2.3), with 91 per cent more than 1.5. 

 nigripinnis, (1.1) 1.3-1.5 (1.7), with 6 per cent more than 1.5. 

 L/D: 



artedi, (3.7) 4.3-5 (5.9), with 80 per cent more than 4.3. 

 nigripinnis, (3.2) 3.6-4.3 (4.6), with 5 per cent more than 4.3. 



In addition, nigripinnis has, on the average, the margin of the pectoral more 

 decurved, a longer snout, and fewer lateral-line scales. It spawns in September, 

 while artedi spawns in late November, so that the state of development of the sex 

 organs also may aid in separating specimens of the two forms. 



GEOGRAPHICAL DISTRIBUTION 



Data on the occurrence of the bluefin in Lake Superior, which are presented in 

 Table 44 and shown platted on the chart in Figure 3, have been derived, for the most 



17 Figures given in this section for proportions are for specimens chiefly over 225 millimeters in length. Counts are given for 

 specimens of all sizes. 



