Fish Hatchery Management - fisheries & aquaculture

I rl0 I:lSH llA lCHl.lRY NIANi\(;U\{l.tN- If'he fish are allowed to prepare nests or spawning sites as they might inthe wild.SALN{ONII) I'ISHI.]SIn salmonid culture, spawning channels have been used in conjunctionwith natural spawning. In a spawning channel, mature fish are allowed tospawn naturally. The channel has a carefully constructed bottom type anda controllable water flow. Typically, the channel has a carefully gradedbottom of proper gravel types, approximately I foot thick. Over this, therewill be a minimum water level of 1.5 to 2.5 feet. The size of gravel used forthe spawning or incubation areas should pass a 4-inch screen but not a0.75-inch screen. Siltation can kill large numbers of eggs and fry so Propersilt entrapment devices must be provided. The gravel bottom must beloosened and flushed periodically in order to maintain proper water velocitiesand percolation through the gravel. Invert controls or sills placed atintervals across the bottom of the channel also are important. Theseprevent the gravel from shifting downstream and also help to maintainproper percolation of water through the gravel.The density of eggs in a spawning channel is controlled by the spawningbehavior of each species. For example, spawning pink salmon use 10square feet of bottom per pair of fish; sockeye or chum salmon use 20square feet per pair. Densities of spawners that are too high will lead towastage of eggs through superimposition of redds (nests). The final numberof newly fertilized eggs deposited in a spawning channel will not exceed200 eggs per square foot of surface area and may be considerably less thanthis number, even with an optimum density o[ spawners.A typical spawning channel requires at least I cubic foot per second waterflow per foot of channel width during incubation of eggs and fry. Thevolume of flow should be approximately doubled during the spawningperiod to provide adult fish with adequate water for excavation of redds.Spawning channels are not suited for small streams or locations with littlerelatively level land that can be easily shaped with heavy machinery.In general, channels have been most successful with pink, chum, andsockeye salmon. Chinook and coho salmon do not fare as well. Improvedresults with chinook salmon have been reported when emerging fry areretained in the channel and fed artificial diets prior to their release. Experimentswith Arctic char suggest that this species also might adapt to spawningchannels.WA I{MW A'I' I.]R. I.'ISH I,SNatural spawning methods are used extensively with warmwater species offish such as bass, sunfish, and catfish. Pond-water depth is i']-5 feet in the