296 PRACTICAL ZOOLOGY 



When the boxes reach the hatchery, the trays are removed and 

 the eggs transferred to other trays that fit into the hatching 

 troughs. Each of these trays holds 6000 eggs, and one hatch- 

 ing trough when filled contains 5,000,000 eggs. Cold water is 

 kept continually flowing over the eggs at the rate of seven 

 gallons per minute. Every three days the trays are carefully 

 examined and all eggs that are dead or are attacked by fungous 

 diseases are picked out. 



The eggs begin to hatch in from 75 to 90 days according to 

 the temperature of the water. They are shipped to the waters 

 in which they are to be planted shortly before they hatch, or 

 else they are allowed to hatch and the young fry are planted. 



The methods of propagation depend upon the habits of the 

 fish and the weight of the eggs. Fishes that do not care for 

 their eggs or young, like the lake trout and whitefish, can be 

 propagated as described above. Other species, like the black 

 bass, lay a lesser number of eggs, but guard them. Such fish are 

 kept in ponds and protected during the spawning season. 

 Eggs like those of the lake trout are heavy and must be 

 spread out in thin layers on trays, but the comparatively light 

 eggs of such fish as the whitefish are hatched in glass jars, 

 each jar containing five quarts or 200,000 eggs. Water 

 must flow through these trays or jars continually. 



Work of the United States Bureau of Fisheries. - - The United 

 States Bureau of Fisheries was organized in 1871 as an independ- 

 ent institution, but in 1903 it was included in the new Depart- 

 ment of Commerce and Labor. It consists of three principal 

 divisions : (i) Fish Culture, (2) Scientific Inquiry, and (3) Sta- 

 tistics and Methods of the Fisheries. 



Some idea of the work done along fish cultural lines may be 

 gained from the preceding paragraphs on the artificial propaga- 

 tion of fishes. The efforts of the bureau have not been limited 

 to fish, however, but the propagation of lobsters, oysters, 

 sponges, fresh-water mussels, and diamond-back terrapins has 

 been studied and in most cases successfully accomplished. 



