Areas selected for spawning are in fast moving riffle areas of a 

 stream on gravel and rubble bottom free of silt. Size of the redd, con- 

 structed by the female, varies from one foot to two feet wide and from 

 two feet to four feet long, depending on the size of the spawning fish. 

 Excavation of a rainbow trout redd in the Kennebec River study con- 

 firmed the efficient fertilization of naturally spawned eggs. 



At the time the eggs are laid, water temperatures are in the low 

 forties, and egg development is slow. As the water warms, the eggs de- 

 velop more rapidly. At an average water temperature of 50 F., hatch- 

 ing takes place about 30 days after the eggs are laid in the gravel. 

 Young rainbows remain buried in the gravel until the yolk sac is en- 

 tirely absorbed. When the reserve food of the yolk sac is used young 

 rainbow move up through the gravel to the flowing stream. The fish are 

 now known as advanced fry. In the Kennebec River study fry emerged 

 from the nest by July 15. 



Feeding begins on minute particles of food that flow by as the small 

 fry remain on, or near, the stream bottom. Food of young rainbow trout 

 consists of insects and crustaceans and, as they reach adulthood, fish be- 

 come an important item of the diet. At the end of the first summer of 

 growth, young rainbows will be three to four inches in length, and are 

 known as fingerlings. At this time the parr markings of dusky vertical 

 bands on the sides are clearly visible. Some rainbows move downstream 

 as advanced fry, some remain in the stream a year or more, and others 

 may become resident in the stream of their birth and remain throughout 

 their life in a limited area. 



Age and growth of 41 rainbow trout taken by fishermen in the 

 Kennebec River and tributaries from Pleasant Pond Stream in Caratunk 

 to Solon Dam in Solon foflow: 



Age 



The rainbow trout in the Kennebec River attain legal length (6 

 inches) in September of their second summer of growth. Six specimens 

 taken by anglers in September averaged 8.9 inches in total length. The 

 bulk of the fishery is made up of fish in age groups 2 and 3 in their third 

 and fourth summer of growth. 



Rainbow trout will probably always be limited in their distribution 

 in Maine. They seem to demonstrate greater migratory tendencies than 

 cither brook or brown trout and this characteristic tends to make it dif- 

 ficult to establish the species. Feeding habits and spawning requirements 



40 



