AETIFICIAL PROPAGATION OF PACIFIC SALMONS. 29 



After all the eggs are hatched and the baskets and riffle dams are 

 removed from the troughs, each trough is divided into three equal 

 compartments for holding a certain proportion of fry by inserting 

 in the saw scarfs which carry the riffle dams 7 by 14S inch screens, 

 made of No. 9 gauge zinc. The size of the perforations, which are 

 horizontal in shape, should be governed by the species handled, and 

 the four outer edges of each screen should have a one-half inch mar- 

 gin of unperforated metal. The number of fry that can be held until 

 the absorption of the yolk sacs ranges from 30,000 to 50,000 per 

 trough, varying with the species and the water supply available. 



In the deep trays the newly-hatched fish are mixed with unhatched 

 eggs, and the advantage of the oblong mesh in the bottom of the 

 trays becomes apparent. This mesh is too narrow to allow the eggs 

 to fall through, but the hatched fish, being comparatively long and 

 narrow, easily slip through the long mashes into the space below. 

 They should be assisted by gently raising and lowering the tray at 

 intervals, taking care not to raise them out of the water, as at this 

 tender age a slight pressure against the wire of the tray will often 

 produce fatal injuries. On this account too much caution can not 

 be exercised in regard to handling them out of water during the first 

 stages of the yolk-sac period, for the injuries can not be seen at first, 

 and often the death of the fry is the first warning that they have been 

 injured. 



After the eggs are all hatched and the young fish are safely out of 

 the trays and on the bottom of the troughs, their dangers are few, 

 and they require comparatively little care. Almost the only thing 

 to be guarded against at this period is suffocation. Even where 

 there is an abundance of water and room, with a good circulation, 

 thej often crowd together in heaps, or dig down under one another 

 until some of them die from want of running water, which is not an 

 inch away from them. The best remedy in such a case is to thin 

 them out. 



FEEDING THE FRY. 



In recent years it has become well recognized that real success in the 

 propagation of the Pacific salmons is determined in large measure 

 by the extent to which the young are reared to the fingerling stage 

 before liberating. The former practice of planting defenseless fry 

 in wholesale numbers a short time before the final absorption of the 

 yolk sac is now almost obsolete. This pertains particularly to the 

 blueback and silver salmons and in less degree to the chinook, for 

 these are known to pass a part or the whole of their first year's exis- 

 tence in fresh water, a period of residence that has been determined 

 conclusively, chiefly as the result of general investigations and study 

 of salmon scales conducted in recent years by Dr. C. H. Gilbert, of 

 Stanford University, Calif. 



The demand for fingerlings which has naturally followed this 

 recognition of the great value of fingerlings over fry has developed 

 the necessity for a cheap food, one that will furnish proper nourish- 

 ment for the young fish and be available in large quantities, as the 

 cost of liver, which has long been a favorite article of food for young 

 fish on the west coast, has become prohibitive, except for occasional 

 use and to afford a change of diet for a short period. 



