CHAPTER XX 
SALMONIDZA 
or allies of the salmon and trout, are characterized as a 
Ws) whole by the presence of the adipose fin, a struc- 
eure 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 remote. 
Probably these groups all have a common descent from some 
primitive fish having an adipose fin, or at least a fleshy fold on 
the back. 
Of all the families of fishes, the one most interesting from 
almost every point of view is that of the Salmonide@, the salmon 
family. As now restricted, it is not one of the largest families, 
as it comprises less than a hundred species; but in beauty, 
activity, gaminess, quality as food, and even in size of indi- 
viduals, different members of the group stand easily with the 
first among fishes. The following are the chief external charac- 
teristics which are common to the members of the family: 
Body oblong or moderately elongate, covered with cycloid, in 
scales of varying size. Head naked. Mouth terminal or some- 
what inferior, varying considerably among the different species, 
those having the mouth largest usually having also the strongest 
teeth. Maxillary provided with a supplemental. bone, and 
forming the lateral margin of the upper jaw. Pseudobranchize 
present. Gill-rakers varying with the species. Opercula com- 
plete. No barbels. Dorsal fin of moderate length, placed 
near the middle of the length of the body. Adipose fin well 
developed. Caudal fin forked. Anal fin moderate or rather 
long. Ventral fins nearly median in position. Pectoral fins 
inserted low. Lateral line present. Outline of belly rounded. 
Vertebrz in large number, usually about sixty. 
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