34 U. S. BUREAU OF FISHERIES. 



repeated plants of rainbow trout have failed to give results, the fish 

 apparently seeking an outlet to the sea. Whether unsuitable condi- 

 tions in the streams are responsible for this failure or whether it is 

 due to some extent to a possible cross with the anadromous steelhead 

 is a matter for conjecture. 



The theory has been held that this species would serve for stocking 

 streams formerly inhabited by the brook trout {SalveUnus fonti- 

 Tialis), in which the latter no longer thrives owing to the clearing 

 of the land at the sources of the streams, which has changed condi- 

 tions in and along the waters, so that they are not agreeable to the 

 brook trout's wild nature. It has been believed generally that the 

 rainbow trout is adapted to warm^- and deeper waters and there- 

 fore is suited to many of the now depleted streams which flow from 

 the mountains through the cultivated lands of the valleys. This 

 theory is disputed by Meehan, Bean, and other fish-culturists, how- 

 ever. 



Rainbow trout, particularly the smaller sizes, differ from brook 

 trout and other predacious fishes in that they feed principally upon 

 worms, larvse, Crustacea, and the like, and do not take readily to 

 minnows as food. They should be planted in spring or early sum- 

 mer, when their natural food is abundant, as they will then grow 

 more rapidly and become accustomed to life in the stream, and when 

 worms, larvae, etc., are no longer to be found their experience and 

 size will enable them to take a minnow or anything that may present 

 itself in the shape of food. 



SIZE AND GROWTH. 



The size of the rainbow trout depends upon its surroundings, the 

 volume and temperature of the water, and the amount of food it con- 

 tains. The average weight of those caught from streams in the 

 East is probably less than a pound, but some weighing 6| pounds 

 have been taken. In the Ozark region of Missouri they are caught 

 weighing 5 to 10 pounds. In some of the cold mountain streams of 

 Colorado their average weight is not more than 6 or 8 ounces, but in 

 lakes in the same State, where the water becomes moderately warm in 

 summer and food is plentiful, they reach 12 or 13 pounds and a 

 length of 25 to 28 inches. In the Au Sable River, in Michigan, they 

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

 fornia they are often caught ranging from 3 to 10 pounds, but av- 

 erage from 1 to 2 pounds. The largest specimen ever produced 

 in the ponds at Wytheville and fed artificially weighed 6^ pounds, 

 but many others in the same ponds weighed from 1 to 3 pounds. It 

 is possible that Salvio shasta might be more successful in the southern 

 range of the rainbow trouts, and that "steelhead" rainbows might 

 thrive better in the northern range. 



Under favorable artificial circumstances rainbow trout hatched 

 January 1 should absorb the yolk sac in about 30 days in a mean 

 water temperature of 55° F. At this time feeding begins, and if 

 properly cared for and supplied with a sufficient amount of suita- 

 ble food the young trout should attain the following sizes: 1 

 year old, 8 to 10 inches; 2 years old, 12 to 14 inches; 3 years old, 16 

 to 18 inches. In the open waters of natural lakes and streams their 

 sizes probably would average about 2 inches less per year. 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, 



