MANUAL OF FISH-CULTURE. 73 



same State, where the water becomes moderately warm in summer 

 and food is plentiful, they reach 12 or 13 pounds, fish of this size being 

 from 25 to 28 inches long. In the An Sable Eiver, in Michigan, they 

 attain a weight of 5 to 7 pounds. In their native streams of California 

 they are often caught ranging from 3 to 10 pounds, but average from 

 1 to 2 pounds. The largest specimen ever i^roduced in the jionds at 

 Wytheville, and fed artificially, weighed 0.4 pounds, but many others in 

 the same ponds weigh from 1 to 3 pounds. 



The average growth of the rainbow trout under favorable artificial 

 circumstances is as follows: One year old, from f to 1 ounce; 2 years 

 old, from 8 to 10 ounces; 3 years old, from 1 to 2 pounds; 4 years old, 

 from 2 to 3 pounds. They grow until they are 8 or 10 years old, the 

 rate diminishing with age. Some grow much faster than others under 

 the same circumstances, but the rate of growth is largely a question of 

 food, temperature of water, and extent of the range. In water at 60°, 

 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 compara- 

 tively high temperature if it is plentiful and running with a strong 

 current, but sluggish and shallow water, even with a temperature 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 condi- 

 tion 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 spriug 

 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 inferior to the 

 brook trout in these respects. 



SPAWNING-PONDS. 



In constructing ponds, one of the first considerations is to place the 

 fish absolutely under the control of the fish-culturist, that he may be 

 able to handle them without delay or inconvenience. At Wytheville 

 they are constructed entirely of wood, about 15 by 50 feet and 3 to 3h 

 feet deep, and shaped as shown in i^late 22, and have been found very 

 satisfactory. Excellent water circulation is obtained in all parts, and 

 there are no corners for refuse to lodge in. The bottom of the pond is 

 built M'ith a gradual elevation, in the direction of the upper end, of 2 

 inches in the entire length of the pond. This makes it practically self- 

 cleaning; nearly all of the foul matter will pass off and any remainder 

 can be disposed of by drawing the water down low for a short period 

 and then flushing the pond with fresh water. This method obviates the 

 necessity of handling the fish, which is very important, especially when 

 near the spawning time. 



