152 



LOWER VERTEBRATES. 



in great part true to the extraordioary variability in appearance of the different species 

 of salmon. These variations are, as vi^ill be seen, due to several different causes, 

 notably to differences in surroundings, in sex, and in age. 



The writer and his associate, Professor Charles H. Gilbert, have had, under the 

 auspices of the United States Fish Commission, better opportunities to study the dif- 

 ferent species of Oncorhynchiis than have fallen to the lot of any other ichthyologists. 

 The following discussion of the different species is condensed from our report to the 

 U. S. Census Bureau, portions of which were published in the American Naturalist 

 for March, 1881. Similar conclusions have been independently reached by Dr. T. H. 

 Bean, who visited Alaska in 1880. 



There are five species of salmon {Oncorhynchus) in the waters of the North 

 Pacific. We have at present no evidence of the existence of any more on either the 

 American or the Asiatic side. 



These species may be called the quinnat or king salmon, the blue-black salmon or 

 red fish, the silver salmon, the dog salmon, and the hump-back salmon, or Oncorhyn- 



FiG. 98. — Oncorhynchus tchatoytcha, young male quinnat or king salmon, 



chus tchmeytcha, ner/ca, /cisutch, keta, and gorbuscha. All these species are now 

 known to occur in the waters of Kamtschatka as well as in those of Alaska and 

 Oregon. 



These species, in all their varied conditions, may usually be distinguished by the 

 characters given below. Other differences of form, color, and appearance are abso- 

 lutely valueless for distinction, unless sjDecimens of the same age, sex, and condition 

 are compared. 



The quinnat salmon {Oncorhynchus tchaioytcha) has an average weight of 

 22 pounds, but individuals weighing 70 to 100 pounds are occasionally taken. It has 

 about 16 anal rays, 15 to 19 branchiostegals, 23 (9-M-i) gill rakers on the anterior 

 gill arch, and 140 to 185 pyloric ccEca. The scales are comparatively large, there 

 being from 130 to 155 in a longitudinal series. In the spring the body is silvery, 

 the back, dorsal. fin, and caudal fin having more or less of round black spots, the sides 

 of the head having a peculiar tin-colored metallic lustre. In the fall the color is often 

 black or dirty-red, and the species can only be certainly distinguished by its technical 

 characters. 



The blue-back salmon {OncorhyncMis nerha) usually weighs from 5 to 8 pounds. It 

 has about 14 developed anal rays, 14 branchiostegals, and 75 to 95 pyloric coeca. The 

 gill rakers are more numerous than in any other salmon, the number being usually about 

 39 (16-f 23). The scales are large, there being 130 to 140 in the lateral line. In the 



