150 BULLETIN OF THE BUREAU OF FISHERIES. 
ereatly. In certain localities more or less isolated some of these variations are so 
correlated that the forms would readily be taken for distinct species or even genera 
were not intermediate forms found in other equally isolated localities. 
Agosia robusta varies greatly in scales of lateral line (49 to 77), length of fins, 
development of barbel and lateral line, and general shape of body and head. 
Salmo irideus varies greatly in number of scales, 116 to 176 cross rows. There 
are almost as many variations in color as there are streams. 
ANADROMOUS SPECIES. 
Oncorhynchus gorbuscha (Walbaum). Humpback Salmon. 
Reported from the Sacramento River by Jordan & Gilbert. Not otherwise known from the basin. 
Oncorhynchus keta (Walbaum). Dog Salmon. 
Very rare. One or two seen each year at the canneries and hatcheries. 
Oncorhynchus tschawytscha (Walbaum).@ Sacramento Salmon. 
By far the most important fish of the basin. Ascends the river in two distinct runs, one in May 
and June, the other in September, though a few fish may be found in the river at any time of the year. 
The principal spawning streams, named in the order of their importance, are: The main river between 
Chico and Redding, Battle Creek, McCloud River, upper Sacramento River (above mouth of Pitt 
River), Hat Creek, and Fall River. The importance of Pitt River below the falls as a spawning stream 
is unknown. A few salmon pass up Feather River and most of the other tributaries. The spring run 
spawns in August, the fall run in November. The young of this species begin their seaward migration 
as soon as they are able to swim and reach the ocean when 4 or 5 months old, though a few remain in 
the headwaters until they are 6 to 12 months old. 
Oncorhynchus kisutch (Walbaum). Silver Salmon. 
Reported by Jordan & Jouy, 1881, from the Sacramento River, but not otherwise known from 
the basin. 
Salmo gairdneri (Richardson). Steelhead. 
Reported from the Sacramento River by Jordan & Gilbert, 1881. If it is found in the basin we 
have been unable to distinguish it from the rainbow trout. A specimen weighing 74 pounds, taken at 
Battle Creek hatchery in November, 1897, was identified by us as Salmo irideus. Scales in lateral line 
(not cross rows) 129. 
Osmerus thaleichthys Ayres. 
Taken in fresh water at Walnut Grove and Collinsville. The adults go up the river to spawn during 
February, the young come down during April. 
aFor a more complete account of this fish see Rutter, Natural history of the quinnat salmon, Bulletin U. S. Fish 
Comm., vol. XXII, 1902, p. 65-141. 
