THE SALMON. 



113 



is naked in the whole family. The maxillary bones form the sides of the jaws. There is always a small 

 fatty fin behind the dorsal fin. The air-bladder is large and simple. The eggs fall into the abdominal 

 cavity before they are deposited. These fishes are chiefly found in the fresh waters of the temperate and 

 arctic regions of the northern hemisphere, though the genera Argentina and Microstoma are marine, 

 and never enter livers ; and the New Zealand Smelt (Retropinna. richardsonii) is found only in the 

 rivers of New Zealand. 



THE SALMON.* 



In the summer the Salmon is caught in the estuaries of British rivers. Its form is too 

 well known to need detailed description. The belly is silvery- white, as is the anal fin and the 

 outer side of the ventral fin, the under side of which is dusky, and approaches in colour to the 

 dusky black of the caudal, dorsal, and pectoral fins. The head in its upper part and the back arc 

 of a bluish-black colour. Often there are a few dark spots extending over the body above the lateral 

 line, and they are commonly more numerous in the female than in the male. Low down on the 

 back, just behind the anal fin, is a small second dorsal fin, formed chiefly of fat, and unsupported 

 by bony rays. The first dorsal fin, in which the rays are strong, is placed about the middle of 



the length of the body, nearer to the head than the tail, and the ventral fin is situate somewhat 

 laterally below its middle or hinder part. In the mouth, teeth occur on all the maxillary bones, but 

 in the upper jaw they also extend in the median line on the bone, called the vomer, and form an arch 

 on the palatine bone. There are usually twelve bony rays for the support of the gills, but the number 

 varies. The form of the operculum is one of the best characters for distinguishing the Common 

 Salmon from the species to which it is allied, for its posterior outline is part of a circle. 

 The scales are very small. There are 120 in the lateral line, 25 rows above it, and 18 below. 

 There are about sixty vertebrae in the skeleton. The appendages to the commencement of the 

 intestine, which represent the pancreas, number from sixty-three to sixty-eight. Salmon come up 

 from the sea to spawn in rivers at various periods during the spring and summer. It has been 

 observed that the fish are always late in going up those rivers which become muddy and swollen in 

 the spring by the melting of snow on the mountains, but that rivers which have deposited their 

 sediment in lakes, and thus become limpid, furnish the earliest supply of Salmon. Yarrell has 

 drawn attention to the fact that in early spring all the Salmon which enter the river Oykill, in 

 Sutherlandshire, diverge at about five miles from its mouth into its tributary, called the Shin, 

 which rises in a large and deep loch, where, owing to the mass of water, the temperature is 

 warmer, while later in the season the Salmon pass on up the main course of the Oykill, which 

 has then become warmer. 



It has also been noticed that in Cumberland the fish prefer the river Eden to the 

 Esk, though both rivers empty into the same estuary. The Salmon ascend the river with 

 the flood, and generally retire with the ebb of the tide. The female fishes appear before the 



Sal mo salar. 



205 



