GREAT LAKES COREGONIDS 



419 



VARIATIONS 



Too few specimens are available for a study of local variations, and there is no 

 material for a study of variation with growth, as none of the collected specimens are 

 less than 220 millimeters in length. The smallest specimen collected measures 220 

 millimeters and is mature, but occasional much larger specimens in the collection 

 are immature. 



COMPARISONS 81 



Small blackfins bear a superficial resemblance to the kiyi, from which they may 

 be distinguished by their more numerous gill rakers (which in the blackfin are seldom 

 less than 44 and in the kiyi not usually more than 42) and by their more heavily pig- 

 mented fins, especially the ventrals, which are always more or less black in the former 

 but usually immaculate in the latter. The blackfin has a wider body and thicker 

 belly walls, a deeper and blunter head, and somewhat shorter paired fins. Females 

 of the two species may be separated by the state of development of the ova. The 

 blackfin spawns in late December and early January and the kiyi in October. 



Only small nigripinnis could be confused with Jioyi, as the former grows much 

 larger. Nigripinnis is distinguished from fioyi by the body shape, which in the former 

 is ovate, seen from the side, and in the latter elliptical; by the more numerous gill 

 rakers on the first branchial arch and scales in the lateral line; and by the much 

 darker coloration, particularly on the abdominal fins, which in the bloater are often 

 immaculate and never conspicuously pigmented, while in the blackfin all of them are 

 usually conspicuously black. The characters that can be expressed in figures are 

 compared below: 

 Gill rakers on the first branchial arch: 



nigripinnis, (41) 46-50 (52), with 81 per cent more than 45. 



hoyi, (37) 41-44 (48), with 5 per cent more than 45. 

 Lateral-line scales: 



nigripinnis, (74) 80-87 (89), with 90 per cent more than 77. 



hoyi, (60) 67-77 (84), with 7 per cent more than 77. 



The pectoral fins probably average a trifle longer in nigripinnis. The state of 

 the sex organs also should serve often as a criterion in distinguishing at least ques- 

 tionable females, as hoyi spawns in March, nigripinnis in January. Individuals of 

 nigripinnis under 200 millimeters in length probably would not be found often to 

 be sexually mature, while hoyi are regularly mature as small as 140 millimeters. 



Nigripinnis differs from artedi chiefly in the body shape^ which is ovate in 

 side view in the former and elliptical in the latter, and in the longer paired fins and 

 greater body depth. The comparative figures for the last-named characters follow: 

 Pv/P: 



nigripinnis, (1.5) 1.6-1.8 (2.2), with 18 per cent more than 1.8. 

 artedi, (1.6) 1.9-2.2 (2.6), with 94 per cent more than 1.8. 

 Av/V: 



nigripinnis, 1.2-1.5 (1.6), with 8 per cent more than 1.5. 

 artedi, (1.4) 1.6-1.8 (2.3), with 89 per cent more than 1.5. 

 L/D: 



nigripinnis, (3.2) 3.4-3.9 (4.3). 



artedi, (3.6) 4.0-4.9 (5.3), with 62 per cent more than 4.3. 



B Figures given in this section for proportions are based on specimens 200 millimeters or more in length, except artedi, where 

 he limit is 225 millimeters. Counts are given (or specimens of all sizes. 



