FISH-CULTURAL PRACTICES IN THE BUREAU OF FISHERIES. 701 



increase of the numbers of young by protecting the eggs and providing the 

 most favorable conditions for hatching. The other is fish culture also, but in 

 addition to conservation of a resource that would otherwise be imavailed of. 



Some of the freshwater species, valued chiefly as game fishes although 

 marketed also, are cultivated by confining them under conditions which will 

 secure the maximum reproduction by natural processes. Practically all of the 

 important commercial fishes, however, can be propagated, and much more 

 numerously, by stripping them of eggs and milt by hand and incubating the 

 fertilized eggs in hatcheries. It is with these that the Bureau is most largely 

 concerned, their numbers being nearly 98 per cent of the entire output of the 

 hatcheries. 



There are some variations in the methods of spawn taking, according to species, 

 but in general the operation consists in expelling the eggs by a gentle pressure 

 of the thumb and forefinger along the walls of the abdomen, the strokes being 

 continued until all ripe eggs have been secured. The fish is usually grasped 

 near the head, and to hold it firmly may be pressed against the body of the 

 spawntaker. The receptacle into which the eggs are expelled is usually a 

 6-quart milk pan which has been dipped into the water and then emptied, thus 

 leaving it slightly moist. Other forms of receptacles, such as marbleized or 

 porcelain-lined pans or wooden vessels are sometimes used where the eggs are 

 especially adhesive. The milt is obtained by the same process as the eggs, and 

 applied to the latter in the pan used to receive them from the fish. 



The hatching processes are, generally speaking, of three classes with respect 

 to equipment, determined primarily by the specific gravity of the eggs. Heavy 

 eggs, such as those of the trouts, salmons, and the grayling, are incubated in 

 wire-bottom trays or wire baskets set in troughs of running water. The mesh 

 of the wire is of size to suit the size of egg and to perm.it the young fish as they 

 hatch to drop through into the trough. The troughs are usually plain open 

 boxes varying in length from 12 to 16 feet and in depth from 4 to 1 2 inches, to 

 suit conditions. An arbitrary width of 14 inches, inside measure, has-been 

 adopted, uniformity in width being desirable for economy in interior equipment. 

 For handling large quantities of eggs the troughs are frequently provided with 

 either permanent or removable partitions to regulate the direction of the current 

 of water through the eggs. Thus they may be converted into so-called William- 

 son and Clark- Williamson types of troughs. 



Semibuoyant eggs, such as those of the whitefish, pike perch, shad, yellow 

 perch, and white perch, are usually hatched in glass jars. The styles of jar are 

 in general two — closed top and open top, the McDonald Universal hatching jar 

 being of the former pattern, the Chase, McDonald open-top, and Downing being 

 typically the latter. 



