150 FISH HAICHERY MANAGEMENT 



The fish are allowed to prepare nests or spawning sites as they might in 

 the wild. 



SALMONID FISHES 



In salmonid culture, spawning channels have been used in conjunction 

 with natural spawning. In a spawning channel, mature fish are allowed to 

 spawn naturally. The channel has a carefully constructed bottom type and 

 a controllable water flow. Typically, the channel has a carefully graded 

 bottom of proper gravel types, approximately 1 foot thick. Over this, there 

 will be a minimum water level of 1.5 to 2.5 feet. The size of gravel used for 

 the spawning or incubation areas should pass a 4-inch screen but not a 

 0.75-inch screen. Siltation can kill large numbers of eggs and fry so proper 

 silt entrapment devices must be provided. The gravel bottom must be 

 loosened and flushed periodically in order to maintain proper water veloci- 

 ties and percolation through the gravel. Invert controls or sills placed at 

 intervals across the bottom of the channel also are important. These 

 prevent the gravel from shifting downstream and also help to maintain 

 proper percolation of water through the gravel. 



The density of eggs in a spawning channel is controlled by the spawning 

 behavior of each species. For example, spawning pink salmon use 10 

 square feet of bottom per pair of fish; sockeye or chum salmon use 20 

 square feet per pair. Densities of spawners that are too high will lead to 

 wastage of eggs through superimposition of redds (nests). The final number 

 of newly fertilized eggs deposited in a spawning channel will not exceed 

 200 eggs per square foot of surface area and may be considerably less than 

 this number, even with an optimum density of spawners. 



A typical spawning channel requires at least 1 cubic foot per second wa- 

 ter flow per foot of channel width during incubation of eggs and fry. The 

 volume of flow should be approximately doubled during the spawning 

 period to provide adult fish with adequate water for excavation of redds. 

 Spawning channels are not suited for small streams or locations with little 

 relatively level land that can be easily shaped with heavy machinery. 



In general, channels have been most successful with pink, chum, and 

 sockeye salmon. Chinook and coho salmon do not fare as well. Improved 

 results with chinook salmon have been reported when emerging fry are 

 retained in the channel and fed artificial diets prior to their release. Exper- 

 iments with Arctic char suggest that this species also might adapt to spawn- 

 ing channels. 



WARMWATER FISHES 



Natural spawning methods are used extensively with warmwater species of 

 fish such as bass, sunfish, and catfish. Pond-water depth is 3-5 feet in the 



