ARTIFICIAL PROPAGATION OF TROUT. 35 



but the rate of growth is largely a question of food, temperature of 

 water, and extent of the range. In water at 55°, with plenty of food, 

 fish 1 or 2 years old will double their size several times in a single 

 season, while in water at 40° with limited food the growth is scarcely 

 perceptible. 



The rainbow, like the brook trout, will live in water with a com- 

 paratively high temperature if it is plentiful and running with a 

 strong current, but sluggish and shallow water, even with a tempera- 

 ture of 70° F., is dangerous for brook trout. Rainbow trout will 

 live in warmer water than brook trout and are found in swift, rapid 

 streams at 85° F., especially where there is some shade, but in ponds 

 that temperature is dangerous even with shade and a good current. 

 In its natural condition this trout is usually found in water varying 

 from 38° F. in winter to 70° F in summer, and in selecting a site 

 for a trout hatchery spring water with a temperature of 42° to 58° 

 is required. 



The rainbow trout is a superior game fish, a vigorous biter, and 

 fights bravely for liberty, though in the east it is somewhat infe- 

 rior to the brook trout in these respects. - . 



PROPAGATION. 

 WATER SUPPLY. 



The best water supply for a trout hatchery is that taken from a 

 well-protected and deep-seated sj)ring. The fall between the spring 

 and the hatchery should be sufficient to permit the hatching troughs 

 to be placed about 30 inches above the hatchery floor and to aerate 

 the water as it enters the trough. Water obtained from a spring- 

 fed stream or lake is apt to vary considerably in temperature and to 

 carry much sediment and other foreign matter. While an open 

 supply trough in the hatchery is somewhat unsightly and cumber- 

 some, it seems to produce better results than a closed pipe. For a 

 hatchery with 20 troughs a supply trough 10 inches wide and 10 in- 

 ches deep, inside measurements, will carry sufficient water. A 2-inch 

 molasses gate with a brass face set about 3 inches above the bottom 

 of the supply trough is the best means of regulating the flow of 

 water to the hatchery troughs. The water should have a drop of 

 from 10 to 12 inches as it enters the hatchery supply trough from 

 the main conduit, and it should be further aerated as it enters the 

 hatching troughs. For this reason the supply trough should be set 

 about 6 inches above the top of the hatching troughs with a space of 

 3 or 4 inches from the ends. When local conditions will not permit 

 such means of aeration, the water supply must be aerated as thor- 

 oughly as possible by some other means. 



The mam water supply at the Wytheville (Va.) hatchery is 

 obtained from a spring such as is described above. After heavy 

 rains the water becomes very turbid and much discolored from the 

 yellow clay soil characteristic of the locality. At times the water 

 supply carries sufficient sediment to smother both eggs and newly 

 hatched fry. While this condition is not permanent, it causes much 

 labor and a considerable loss of eggs and fish. 



As the water level from the spring is about 12 feet above the 

 water level in the hatchery supply trough, it was a comparatively 

 easy matter to construct a settling tank and filter. The settling 

 tanJi was built near the spring. Water is conducted from the spring 



