ARTIFICIAL PROPAGATION OF WHITEFISH, ETC. 31 



over the top of the eggs. Unless the shipment is to be in transit a 

 number of days it is not necessary to use moss. When moss is used 

 it is placed between the eggs and the wooden frame of the tray, and 

 frequently some of it is scattered over the top of the eggs, the mos- 

 quito bar preventing it from coming in direct contact with them. 

 The best moss for the purpose is known as sphagnum, which is 

 found in low, swampy places. It should be gathered in the fall 

 when green and stored in a damp place until required. It is well 

 soaked in water before placing it on the trays and the surplus water 

 removed by squeezing a bunch of it between the hands. 



AVhen packed, the egg trays are placed upon an empty tray that 

 has previously been filled with moss, the upper tray of eggs is cov- 

 ered with a tray of moss, and the ice hopper is put in place. Best 

 results will follow if a block of ice is fitted into the ice hopper. 

 In most of the shipments that are destined to points within the 

 United States crushed ice is not used around the egg trays. Ship- 

 ments intended for foreign countries are prepared in the same man- 

 ner, except that moss is placed on each of the egg trays and the 

 outside packing case is provided with a 2-inch thickness of cork 

 insulation. The interior of the case is so arranged as to provide a 

 1^ or 2 inch space all around the egg trays for crushed ice. An 

 ice hopper is also used at the top. These cases are shown in 

 Figure 42. 



FEEDING AND BEARING. 



Lake-trout ivy may be held in troughs and fed, as are the fry 

 of other species of trout. Such a procedure is prohibitive at sta- 

 tions of the Bureau of Fisheries that are concerned with the com- 

 mercial fishery, owing to the impossibility of providing sufficient 

 space and facilities for accommodating the large numbers produced. 

 Moreover, it is the consensus of opinion among scientists and fish- 

 culturists that better results are assured in this field by planting 

 the young fish on the spawning grounds just before the yolk sac is 

 absorbed, at the time w^hen they are known as " free swimmers." 

 At stations of the bureau where small numbers of lake trout are 

 reared for noncommercial purposes the fish are held in troughs 12 to 

 16 feet long, 14 inches wide, and 8 inches deep, inside measurement. 

 A screen compartment about 6 inches wide at the head of the trough 

 prevents the fish from coming in direct contact with the inflow of 

 water, and about 1 inch below it is a dam board extending within 

 one-half inch of the bottom of the trough. At intervals of 18 inches 

 throughout the remaining length of the trough cleats If inches high 

 are mortised across the bottom of the trough. In the sides of the 

 trough just above the cleats saw cuts one-fourth inch deep are made 

 for the insertion of screens, their purpose being to distribute the fish 

 evenly in small compartments throughout the length of the trough. 

 After the fish have been fed for two or three weeks they will adjust 

 themselves to the different parts of the trough, when the screens 

 may be removed. 



A week or 10 days before the disappearance of the yolk sac the 

 fry intended for rearing should be transferred to troughs. A trough 

 14 feet long, supplied with 8 to 10 gallons of water per minute, at 

 a temperature ranging from 45 to 50° F., will support 25,000 fry 



