22 AKTIFICIAL PROPAGATION OF PACIFIC SALMONS. 



the trough, Avith the exception of the space between the second and 

 third and the fourth and fifth compartments. Here the dams are 

 placed 2f inches apart for the accommodation of iron braces, which 

 prevent the troughs from bulging. Only one dam is used at the 

 foot of the trough. This reaches across and extends from the bot- 

 tom to within IJ inches of the top. In the center of the space at the 

 foot of the trough is a 2-inch outlet, provided with a hollow cedar 

 or metal plug, placed at the proper height. The water is thus forced 

 to flow under the upper dam upward through the basket of eggs, and 

 thence over the lower dam, etc. The troughs are provided with can- 

 vas covers stretched upon light frames and made sunproof by satura- 

 tion with asphaltum varnish, which is also thickly applied to the 

 interior surface. 



The egg receptacles are oblong-mesh wire-cloth baskets about 13| 

 inches wide, 24 inches long, and from 5| to 6 inches deep, thus allow- 

 ing them to project an inch or two above the surface of the water 

 in the troughs. When wooden-rimmed baskets are used, the rim rests 

 on the top of the trough and holds the basket 1 inch from the bottom. 

 Arranged in this way the water passes under the riffle dam at the 

 head of the compartment, beneath the basket, and then upward 

 through the eggs. The metal rim, which has been adopted in recent 

 years, is supported by metal lugs fastened to the edge of the basket, 

 rests on the top of the trough, and holds the basket in the same posi- 

 tion as the wooden rim. In both cases the basket, when in operation, 

 should be kept flush against the lower riffle dam of the compart- 

 ment in which it is placed, to force the ascent of the water through 

 the eggs. 



The number of eggs that can be incubated in a basket depends 

 upon the species of salmon and the volume of the water supply. 

 This varies with the chinook from 20,000 to 30,000; blueback, from 

 50,000 to 60,000 ; silver, from 30,000 to 35,000 ; humpback, from 40,000 

 to 50,000 ; and chum, from 33,000 to 38,000. 



The eggs suffer no injury from being in numerous layers, as water 

 is constantly forced through the mass, partially removing the pres- 

 sure. The baskets are constructed of galvanized wire containing 

 from four to six meshes per inch, three-fourths of an inch long, the 

 size of the mesh varying with the size of the eggs to be handled. The 

 oblong mesh permits the fry to pass through onto the bottom of the 

 troughs when hatched, but it is not large enough for the passage 

 of the eggs. The advantages of this apparatus are: (1) The top 

 of the basket is above water, so that the eggs can not overrun or 

 escape; (2) by tilting one end of the basket a little, or by lifting it 

 and settling it back gently in place, the bad eggs are forced to the 

 top and can be easily removed with the ordinary egg picker; (3) 

 space is conserv^ed, as the basket provides many times the number of 

 eggs that could be accommodated on trays with an equal voliune of 

 Avater, the proper flow per trough being from 10 to 15 gallons per 

 minute; (4) the ease and facility with which the mud can be dis- 

 carded make it possible to remove all sediment collecting on the 

 eggs by gently moving the basket up and down in the water several 

 times. 



The period of incubation of salmon eggs depends upon the water 

 temperature. A veiy safe rule to follow is one originally formu- 

 lated by Seth Green: 



