found, and wliere hatcheries are 

 located, are rehxtively soft water. 

 The water should have a dissolved 

 oxygen content of not less than 5 

 parts per million wlien introduced 

 into the trough or pond, but greater 

 oxygen content may be required if 

 ponds or troughs are heavily 

 stocked, depending upon water tem- 

 peratures. 



The numbers and size of fish in 

 a pond or trough, and the water 

 temperature, vrill determine the 

 quantity of water required to be 

 introduced. There is no rule by 

 whicli the number of fish to be 

 stocked may be determined, al- 

 though a pond may be expected to 

 carry up to 1 pound of fish per cubic 

 foot of water. Generally a greater 

 weight of larger fish than of small 

 salmon can safely be carried in a 

 pond or trough, but capacities vary 

 with the species. The maximum 

 carrying capacity of a trough or 

 {)()nd should be determined by trial 

 at each hatchery. The total pound- 

 age should be determined with ap- 

 propriate consideration for pro- 

 longed treatments for disease and 

 for water drawdown when cleaning 

 ponds or removing fish. 



Generally the water supply for 

 the hatchery is drawn from a stream 

 draining an established watershed 

 within which are few if any farms 

 {ind livestock. Such a watershed 

 usually provides impolluted and 

 relatively silt-free water. At some 

 hatcheries it is necessary to provide 

 a sand-gravel filter to remove ob- 

 jectionable silt. 



The availability of spring water 

 with a temperature range of 40° to 

 (^0° F. is desirable to warm winter 



stream waters used in the hatchery. 

 Often warmer waters are needed to 

 promote more rapid growth in order 

 to meet certain planting require- 

 ments. Present knowledge indi- 

 cates, however, that the rearing of 

 some species, particularly spring 

 chinook, shoidd not permit too 

 ra})id growth. The young salmon, 

 if they are reared rapidly to large 

 size (6 to 8 inches) may exliibit a 

 desire to migrate to the ocean in 

 midwinter, when stream conditions 

 are most unfavorable in some locali- 

 ties. 



For the most efficient hatchery 

 production of salmon, the water 

 temperature should range from 

 about 45° to 60° F. Incubation 

 temperatures should be 45° to 55° 

 F., and rearing temperatures of 50° 

 to 60° F. are desirable. Higher 

 temperatures are not to be souglit 

 because of disease development, and 

 lower temperatures retard growth. 



The supply of water for the 

 luitchery may he carried from the 

 source in a pipe or flume ; an earthen 

 ditch is not recommended because 

 of the algae growth and the possi- 

 bility that disease-carrying fish may 

 Cnd the ditch a suitable habitat. 

 Flumes should be covered if leaves 

 and wind-borne debris are present. 

 The intake structure on a stream 

 usually includes a l)ari-ed grill or 

 grissly to exclude logs and large 

 debris, and a revolving or other type 

 screen to remove smaller debris and 

 to divert fish back to the stream. 

 Also at the intake is a \alve or stop- 

 log arrangement for control of the 

 '^ater. 



Water may be introduced into 

 troughs or })onds tlirectly from a 



40 



