1154 EEPOET OF COMMISSIONER OF FISH AND FISHERIES. [ICj 



monoecious, cannot be artificially propagated from the egg like the 

 dioecious American species. 



8. THE METHODS OF ARTIFICIAL PROPAGATION. 



The fertilization of the fisli egg is the simplest of processes, consisting, 

 as every one knows, in simply pressing the ripe ova from the femalefish 

 into a shallow receptacle and then squeezing out the milt of the male 

 upon them. Formerly a great deal of water was placed in the pan ; now 

 the •' dry method," with only a little, discovered by the Bussian, Vrasski, 

 in 1854, is preferred. The eggs having been fertilized, the most difficult 

 part of the task remains, namely, the care of the eggs until they are 

 hatched, and the care of the young fry until they are able to care for 

 themselves. 



The apparatus employed is various in principle, to correspond to the 

 physical peculiarities of the eggs. Fish culturists divide eggs into four 

 classes, viz : (1) Heavy eggs, nonadhesive, whose specific gravity is so 

 great that they will not float, such as the eggs of the salmon and trout; 



(2) heavy, adhesive eggs, such as those of the herring, smelt, and perch; 



(3) semi-buoyant eggs, like those of the shad and whitefish (Coregonus)', 

 and (4) buoyant eggs, like those of the cod and mackerel. 



Heavy, non-adhesive eggs, are placed in thin layers, either upon 

 gravel, grilles of glass, sheets of wire cloth, or i)erforated tin, in recep- 

 tacles through which a current of water is constantly passing. There 

 are luimerous forms of apparatus for eggs of this class, but the most 

 eflective are those in which a number of trays of wire cloth, just deep 

 enough to carry single layers of eggs, are placed, one upon the other, 

 in a box or jar into which the water enters from below, passing out at 

 the top. 



Heavy, adhesive eggs are received upon bunches of twigs or frames 

 of glass plates, to which they adhere and which are placed in recepta- 

 cles through which water is passing. 



Semi-buoyant eggs, or those whose specific gravity is but slightly 

 greater than that of the water, require altogether other treatment. 

 They are necessarily placed together in large numbers, and to prevent 

 their settling upon the bottom of the receptacle it is necessary to intro- 

 duce a gentle current from below. For many years these eggs could 

 be hatched only in floating receptacles i)laced in a river with wire-cloth 

 bottoms, placed at an angle, the motion of which was utilized to keep 

 the eggs in suspension. Later an arrangement of plunging buckets 

 was invented, cylindrical receptacles, with tops and bottoms of wire 

 cloth, which were suspended in rows from beams which were worked 

 up and down at the surface of the water by machinery. The eggs in 

 the cylinders were thus kept constantly in motion. Finally the device 

 now most in favor was perfected ; this is a receptacle, conical, or at 

 least with a constricted termination, placed with its apex downward, 

 through which passes from below a strong current, keeping the eggs 



