THE SALMON FAMILY — SALMONIDAE. 
As at present restricted, the salmon family is not large but comprises some of the most 
highly esteemed game fishes and commercially valuable food fishes. The family is peculiar to 
the northern part of the northern hemisphere, in both salt and fresh water. Species of some of 
the various genera regularly enter the sea, some more or less irregularly, and others not at all. 
There are probably few, if any, species that would not go into salt water if it were conveniently 
accessible. The most valuable species commercially attain most of their growth in the sea and 
enter fresh water for reproduction only. The Pacific Salmon of the genus Oncorhynchus breed 
but once in a lifetime. The family is of recent geological origin as indicated by its structure, 
and very few fossils have been observed. Jordan says, in A Guide to the Study of Fishes : 
“Fragments of fossil trout, very imperfectly known, are recorded chiefly from Pleistocene 
deposits of Idaho, under the name of Rhabdofario lacustris. We have also received from Dr. 
John C. Merriam, from ferruginous sands of the same region, several fragments of jaws of salmon, 
in the hook-nosed condition, with enlarged teeth, showing that the present salmon-runs have 
been in operation for many thousands of years. Most other fragments hitherto referred to 
Salmonidae belong to some other kind of fish.” 
Characterization. 
No one of the external or internal structures usually enumerated as the chief characteristics 
of the salmon family will alone distinguish it. It is only by combinations of them that some 
other forms are excluded. Opinions vary regarding the value of the combinations and a satis- 
factory classification depends upon a thorough knowledge of the comparative anatomy of 
salmonoid and related fishes. From external structures alone, one might more consistently 
exclude the whitefish and admit the grayling and the smelt into the salmon family than to 
accept the present arrangement. 
The osseus structures, especially of the head, afford the most dependable differential char- 
acteristics, but sometimes even these must be used in combination with other structures. Within 
the family the same conditions apply in the separation of other groups as subfamilies, genera, 
subgenera, and species. 
In A Guide to the Study of Fishes, Jordan says: “The series or suborder Salmonoidea, 
or allies of the salmon and trout, are characterized as a whole by the presence of the adipose fin, 
a structure also retained in Characins and catfishes, which have no evident affinity with the 
trout, and in the lantern-fishes, lizard-fishes, and trout-perches, in which the affinity is very 
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