McCloud River Rainbow Trout 



The size of the rainbow trout varies greatly, depending upon 

 the volume and temperature of the water, and the amount and 

 character of the food-supply. In the streams of the Sierras, where 

 it is native, it reaches a length of lo to 30 inches, and a weight 

 of 2 to 8 pounds. The average weight of those caught from 

 streams in the East is probably less than a pound, but examples 

 weighing 6| pounds have been taken. In the Ozark region in 

 Missouri they are caught weighing 5 to 10 pounds. In some of 

 the cold mountain streams of Colorado their average weight is 

 but 6 or 8 ounces, while in certain lakes in the same State, 

 where the water is moderately warm, and food is plentiful, they 

 reach a length of 25 to 28 inches, and a weight of 12 or 13 

 pounds. In the Au Sable River in Michigan they reach a weight 

 of 5 to 7 pounds. The largest example ever produced in the U. S. 

 Fish Commission ponds at Wytheville, Virginia, weighed 6^ 

 pounds. 



The average growth of the rainbow trout under favourable 

 artificial circumstances is as follows: One year old, from f to i 

 ounce; 2 years old from 8 to 10 ounces; 3 years old from i to 2 

 pounds; 4 years old from 2 to 3 pounds. Like all other fishes, 

 they continue to grow, at least until they are 8 or 10 years old, 

 the rate diminishing with age. Some, of course, grow much 

 faster than others, even under the same circumstances, but the rate 

 of growth, as with all fishes, is largely a question of tempera- 

 ture, food, and extent of water-area. In water at 60°, with 

 plenty of food, fish i 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 very slow indeed. 



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

 comparatively high temperature if it is plentiful and running with 

 a strong current; but in sluggish water, even when the temper- 

 ature is considerably lower, neither species will do well. The 

 rainbow, however, will live in warmer water than the brook trout, 

 and is often found in streams where the temperature is as high 

 as 75° or even 85°, especially where there is some shade. The water 

 of the streams in which the rainbow is native, varies in temper- 

 ature from 38° in winter to about 70° in summer. For hatchery 

 purposes spring water, with a temperature from 42° to 58°, is 

 best. 



The spawning season of the rainbow trout in California ex- 



199 



