FISHES OF SACRAMENTO-SAN JOAQUIN BASIN. 141 
18. Salmo irideus Gibbons. Rainbow Trout. 
Salmo iridea Gibbons, Proc. Cal. Ac. Nat. Sci. 1856, p. 36, San Leandro Creek, San Francisco Bay. Jordan & Evermann, 
Fishes North & Mid. Amer., pt. 1, p. 500, 1896. 
Salmo rivularius Ayres, Proc. Gal. Ac. Nat. Sci. 1856, p. 43, Martinez Creek. 
Salar iridea Girard, Pac. Ry. Surv., vol. v1, p. 33, 1857, Chico Creek. 
Salmo tsuppitch Jordan & Henshaw, Wheeler Survey, p. 196, 1878, Kern River and tributary of Pitt River. 
Salmo henshawi Jordan, Wheeler Survey, p. 197, 1878, MeCloud River. 
Salmo pleuriticus Jordan & Henshaw, op. cit., p. 198, South Fork Kern River. 
Salmo mykiss irideus Jordan & Gilbert, Bul. U.S. Fish Comm., vol. xrv, 1894, p. 139, Clear Lake. 
Salmo irideus stonei Jordan, Thirteenth Biennial Report Cal. Fish Comm. 1894, p. 142, McCloud River. Jordan & Evermann, 
op. cit., p. 503. 
Salmo gairdneri shasta Jordan, op. cit., p. 142, same place. Jordan & Evermann, op. cit., p. 502. 
Salmo gairdneri gilberti Jordan, op. cit., p. 143, Kern River. Jordan & Evermann, op. cit., p. 502. 
The most widely distributed species found in the basin. Exceedingly variable. Found in many 
isolated localities, in some of which it has developed into forms more or less peculiar. The following 
variations are worthy of note: 
The common form, found throughout the basin, has the back dusky olive, lower sides and belly 
silvery; back and sides to below lateral line, and dorsal and caudal fins, thickly covered with small 
black spots; a broad, ill-defined, purplish stripe from side of head to base of caudal fin; tips of dorsal, 
anal, and ventrals often white. 
The trout from upper McCloud River are dusky above, pale below, a reddish-brown stripe along 
sides, opercles washed with same; back and sides, dorsal and caudal fins thickly covered with oval or 
round black spots about half size of pupil; belly and lower fins yellowish; tips of dorsal, anal, and 
ventrals white. Very abundant. About six inches long; scales small, 146 to 165. 
The form found in South Fork Battle Creek above the falls closely resembles that found in the 
upper McCloud River. Both forms have finer scales than the average, and those from Battle Creek 
have the finest scales recorded from any locality. The following is a detailed description of the Battle 
Creek specimens: 
Head 3.7 to 4 in length, depth 4 to 4.7; eye 3.5 to 4 in head, snout 4.5 to 5; maxillary 2 to 2.2 in 
head, extending to below posterior margin of eye (specimens 4.5 to 5.8 inches long). Dorsal 11 or 12; 
anal 10 or 11; branchiostegals 10 to 12; gillrakers 5 to 7+10 to 12. Origin of dorsal in middle of body, 
ventrals inserted under fifth ray of dorsal. Height of dorsal 1.7 in head, anal 2.7. Scales small, not 
overlapping, pores in lateral line 114 to 123, cross series of scales 151 to 176, scales before dorsal 66 to 
84, above lateral line 28 to 32, below lateral line 25 to 31. Margin of anal S-shaped, the anterior portion 
convex and longer, the longest rays overlapping shortest by 0.7 the length of the latter. Color brownish 
olive, very faint purplish on sides; very few spots, more numerous on dorsal and adipose fin, few or 
none on caudal; lower fins colorless, parr marks present even in largest specimens. 
Description based on 11 specimens 4.5 to 5.8 inches long. 
The trout of North Fork Feather River near source, locally known as West Fork, are of two forms 
with regard to color. One has very fine black specks thickly scattered over back, dorsal, and caudal 
fins; the other has much larger spots, about the size of pupil. Some specimens have a reddish tinge 
on dentaries, but this is irrespective of other coloration. These variations have been noticed in other 
places, but never so strongly marked as in this locality. 
The Goose Lake trout has the body entirely silvery, with black spots very small and widely sepa- 
rated, not occurring as low as the lateral line. In the few specimens secured the maxillary is longer 
than it is in specimens from other localities; the base of the dorsal fin is shorter, 2.2 in head (1.7 in 
specimens from other localities); dorsal rays 10. 
The trout in a series of small lakes, known as Salmon Lakes, forming one of the sources of North 
Fork of Yuba River, have the sides bright red instead of purplish. The lower fins are of the same 
color as the sides, but edged with white. Some of the trout of Gold Lake, about a mile away from 
Salmon Lakes, but tributary to Middle Fork of Feather River, are red like those from Salmon Lakes; 
others have the ordinary color of typical irideus. The Gold Lake trout are badly infested with gill 
parasites. 
The single specimen from Cliff Lake has but 116 cross rows of scales, which is also the number in 
the lateral line. The average number of scales for the 129 specimens counted is 147. The greatest 
variation in any one locality is 36, found in specimens from Sullaway Creek. Several stations have 
