ARTIFICIAL PROPAGATION OF TROUT. 29 



The introduction of beef liver into the troughs causes a milky dis- 

 coloration of the water. This may be overcome, however, by wash- 

 ing the prepared material before giving it to the fish. The washing 

 process is accomplished by introducing a stream of water into the 

 vessel containing the meat, which is screened to prevent loss of the 

 food, and allowing the milky substance to escape with the overflow. 

 This treatment does not in any way lessen the nutritive value of the 

 food. 



At this stage tl;e young fish have such a precarious hold upon life 

 that too much attention can not be given to their care. Not more 

 than 20,000 can be held with success in a feeding or rearing trough, 

 and a constant circulation of water through the troughs must be 

 kept uj) to prevent disease, while the fish should be properly thinned 

 out in order to prevent loss by suffocation when they increase in size. 

 About 3 to 5 gallons of water per minute are sufficient for 20,000 fry, 

 although this quantity must be increased as the fish grow stronger 

 and are able to breast a heavier current. 



In the spring when the water begins to grow warm the fish require 

 more room than the feeding troughs afford and it is necessary to 

 transfer them to other troughs or ponds. At some of the Federal 

 hatcheries the young trout are held in troughs or nursery ponds until 

 they attain a length of 3 or 4 inches before they are distributed. It 

 has been demonstrated that raceways arranged as described on page 

 31 possess many advantages over troughs for the rearing of such 

 fish. Among the most successful rearing ponds are those from 5 to 8 

 feet wide and not more than 100 feet in length, modeled after the 

 ponds described on page 37. A water supply of about 200 gallons 

 per minute and having a temperature of between 48 and 55° is de- 

 sirable. Ponds of such shape and dimensions may be constructed 

 with natural earth sides from the top of the bank to the water's edge 

 and of cement from the water level to the bottom. The bottoms, 

 with the exception of a feeding area of cement near the outlet, are of 

 gravel. A rearing pond 5 by 20 feet, having a gravel bottom and a 

 flow of not less than 50 gallons of water per minute, will accommo- 

 date from 10,000 to 20,000 fry till midsummer, when the number 

 must be reduced to not more than 5,000. A raceway 4 feet wide and 

 100 feet long, with a strong current, will carry 100,000 fry, and as* 

 the fish develop the number can be reduced and the surplus dis- 

 tributed in other waters or shipped. 



At this stage they are usually fed at regular intervals three times 

 a day, and, as they do not take food readily during the first few days, 

 a great deal of patience is necessary in their treatment and care must 

 be taken to see that no unconsumed portions are allowed to remain at 

 the bottom of the pond and pollute the water. At this time the food 

 should be given in small amounts, and considerable time should be 

 taken to see that it is properly administered. Three-fourths of an 

 hour is not too long for feeding 5,000 fry. The time occupied in 

 feeding should be diminished and the amount of food increased ac- 

 cording to the judgment of the fish-culturist as the fish grow older, 

 but their appetites should never be completely satisfied. 



By early winter all fish reserved for brood stock should have at- 

 tained a length of from 3 to 5 inches. If they have been held in 

 troughs or small ponds, arrangements should be made for their trans- 

 fer to more commodious quarters. A breeding pond 20 feet by 75 feet 



