NO. 1265. SALMONOID FISHES OF JAPAN— JORDAN AND SNYDER. 571 
I. ONCORHYNCHUS MASOU (Brevoort). 
MASU; YEZOMASU. 
Sahno mason Brevoort, Exped. Japan, 1856, p. 275, pi. ix, fig. 2; Hakodate; 
(description from a very bad drawing; 
Oncorhynchus yessoensis Hilgendorf, Monatsber. Ges. Ostasien, XI, 1876, p. 25; 
Hokkaido. 
Head 4 in length; depth 4; depth of caudal peduncle 3i in head; 
snout 4|; eye T; maxillary 2|; D. 13; A. 15; scales in lateral series 
about 190; between lateral line and insertion of dorsal about 29. . 
Interorbital space convex, 3i in length of head; maxillary extending 
considerabh^ be3'ond eye; gill rakers 12+17 on first arch, long and 
slender; branchiostegals 13. Teeth on jaws weak, a few very small 
ones on palatines and vomer. Opercle and preopercle strong!}' convex 
behind; caudal lin forked, strong and short, contained about 5 times 
in the length; pectoral If in head; ventral 2|; the ventral appendage 
almost two-thirds the length of fin. 
Coloration rather dark; sides silver}' ; no distinct black spots on 
bod}' or fins; tip of dorsal and inside of pectorals and ventrals blackish. 
Here described from an immature female specimen in alcohol, 360 mil- 
limeters long, from Aomori. The accompanying figure is taken from 
this specimen. 
This species resembles the Humpback salmon of Alaska and British 
Cohmibia {Oncorliynchus gorhuscha Walbaum). It seems to difl'er, 
however, in the larger scales (about 190) and the larger number of 
branchiostegals, 13 to 16 instead of 11 or 12 as in 0. gorhuscha. The 
caudal fin lacks the large oblong black spots seen in O. gorhuscJia. 
The species also resembles O. Iceta, but can be usually distinguished by 
the smaller size, smaller scales, darker fins, and narrower caudal. The 
tip of the dorsal and the inside of the pectorals and ventrals are very 
large streams; especially abundant in the Cohimbia and Sacramento rivers, where it 
is the principal salmon. The usual order of salmon running in the streams of Oregon 
and Washington is nerka, tschaioyisdia, kisuidt, gorhuscha, and keta. Those which start 
first go farthest. This species ascends the large streams in spring and summer, moving 
up, without feeding, until the spawning season, by which time many of those which 
started first may have traveled more than 1,000 miles. It ascends the Snake River 
to the neighborhood of Upper Salmon Falls, where it spawns in October and Novem- 
ber. In the Salmon River of Idaho it ascends to the headwaters, more than 1,000 
miles from the sea, where it spawns in August and early September when the water 
has reached a temperature of about 54° F. After spawning, most or all of those 
which have reached the upper waters perish from exhaustion. It is by far the most 
valuable of the species of salmon. It has lately been introduced into streams of 
eastern North America, and should be introduced into the streams of Japan, where 
as yet it is unknown. 
{tschau-yisdia, better spelled by earlier writers Tchaviche, the vernacular name in 
Alaska and Kamchatka.) 
