10 FISHES OF THE YELLOWSTONE NATIONAL PARK. 



ARTIFICIAL KEY TO THE FISHES. 



A. Adipose or gristly fin on back situated behind a soft, jointed-rayed dorsal fin. 



Salmonoid fishes. 



B. Anterior dorsal fin long and high, with 19 or 20, or more, fully developed rays. 

 . Graylings (Thymallidse). 



a. Coloration: Back bluish gray with purplish reflections; sides and gill covers 

 lighter, with purple and silvery reflections, beautifully iridescent; scales with 

 pearly luster; belly pure white; a few V-shaped black spots between head 

 and middle of dorsal fin but none posteriorly; two oblong, bluish black blotches 

 in cleft between opercle and gill membrane rays (branchiostegals), more pro- 

 nounced in the male; a line on upper border of belly from ventral to pectoral 

 fins, dark and heavy in the male, very faint in the female. Dorsal fin edged 

 with a red or rosy border; four to seven rows of red or rosy roundish spots, 

 ocellated with white between the dorsal rays; dark blotches forming lines be- 

 tween the rows of red spots. Ventral fins with three rose-colored, branching 

 stripes along the rays, darker between. Pectoral and anal fins plain, with 



dark border i Montana grayling, 1. 



I>B. Anterior dorsal fin short with not over 15 fully developed rays. Salmon family 



(Salmonidse). 



b. Mouth small, teeth sparse, fine bristle-like or none; fewer than 100 fully de- 

 veloped scales in a lengthwise series from the upper end of gill opening to 

 base of tail. Whitefish (Coregoninae). 



c. Scales in longitudinal series 78 to 88; coloration, bluish or grayish olivaceous 



above, silvery on sides, whiter below; sometimes with dusky, or yellowish 

 or brassy tinge; all fins usually tipped with black; tail and adipose fins 

 bluish or olivaceous. No spots; young with parr marks. 



Native whitefish, 2. 



bb. Mouth large, teeth strong and sharp; scales comparatively small, more than 

 100 in lengthwise series. Salmons, trouts, and chars (Salmoninse). 



d. Scales in lengthwise series fewer than 200, body always more or less black 



spotted. (Salmo.) 



e. Scales more than 130 in lengthwise series; body profusely black spotted. 

 /. Scales in lengthwise series about 160 to 170; spots rather large, pro- 

 fusely scattered and irregular, usually none on the belly; red 

 blotches on the lower jaw and membrane between always present. 



Extremely variable in coloration and form Native trout, 3. 



ff. Scales in lengthwise series about 135 to 145; profusely black spotted 

 with only slight if any appearance of red on and between lower 

 jaws. Coloration more or less variable but usually bluish or oli- 

 vaceous above, sides silvery, everywhere profusely spotted, the 

 spots extending on the sides of the belly and on the vertical fins; 

 upper ray of pectoral spotted; spots on tail small, belly nearly plain; 

 both males and females with more or less diffuse red or rosy lateral 

 band and blotches; often much red on cheek and gill cover. 



Rainbow trout, 4. 

 ee. Scales in lengthwise series fewer than 130. Not profusely black 



spotted; no rosy wash, band, or blotches along the side. 

 g. Body comparatively slender, more or less silvery, with 110 ocel- 

 lated red spots; black spots irregular in shape, the shape deter- 

 mined by the number of scales occupied; sometimes cross, double- 

 cross, or triple-cross shape. 



h. Scales in lengthwise series 118 to 130; in oblique cross series from 

 lateral line to upper base of ventral fin 26 to 30. Upper part 



