120 ECONOMIC ZOOLOGY 



transporting young fish from place to place. In 1901 the Bureau 

 planted somewhat over 1,164,000,000 fish in waters of the United 

 States. About Y of these were whitefish and J were shad. 



Many of the individual States have their own fish commissions 

 with numerous hatcheries conveniently located. In Europe there 

 are, or were before the war, more than 400 fish hatcheries, more 

 than half of which were operated profitably by private individuals; it 

 is claimed that a profit of 1500 per cent, had been made in this work. 



The primary object of fish-culture is to increase the proportion of 

 eggs that hatch and to protect the embryos and young fish until they 

 have safely passed the perils, of early life and are able to take care of 

 themselves. As in most animals the young fish are very helpless and, 

 under natural conditions, easily fall prey to various enemies or are de- 

 stroyed by unsuitable environmental conditions; the result is that the 

 struggle for existence is extremely severe and the mortality enormous. 

 Under the artificial conditions of the hatchery natural enemies of the 

 young fish are excluded, and the environment is made as ideal as pos- 

 sible without making it too unnatural. In nature the loss begins with 

 fertilization. Where the eggs are fertilized in the open water of a pond 

 or swiftly running stream it is obvious that many may easily escape 

 coming in contact with spermatozoa; these of course will die and be 

 lost. This loss is almost entirely avoided in the hatchery by the process 

 of " stripping" and artificially mixing the eggs and sperm. In this 

 process the male and female fish are carefully caught, at the time of 

 sexual maturity, and stripped of their eggs and spermatozoa (roe and 

 milt) by holding over a vessel and gently pressing out the roe or milt. 

 Both fish must be ripe or fertilization will not take place. If ripe the 

 belly of the fish feels soft and flabby, and if it be held up by the head the 

 eggs will settle down toward the vent and almost run out without out- 

 side pressure. If not ripe the belly of the fish feels firm and consider- 

 able pressure must be exerted to strip out the eggs. 



The eggs are first stripped into a perfectly clean vessel with a small 

 amount or even no water; then the milt is stripped into the same 

 vessels and the mass gently shaken to insure thorough mixing of eggs 

 and sperm. Fertilization takes place at once; after allowing the mass 

 to stand for 15-20 minutes it is rinsed in clean water and transferred 

 to the hatching trays. By this process from 90 per cent, to 100 per 

 cent, of the eggs will be fertilized and an enormous saving over the 

 natural method will result. 



