BROODSTOCK, SPAWNING, AND EGG HANDLING 



199 



SIMULATED NATURAL CONDITIONS AND REARING POND INCUBATION 



Salmon and steelhead eggs have been incubated successfully between layers 

 of gravel, simulating natural spawning conditions. An incubation box that 

 has proved successful is made of 7-inch marine plywood, 8 feet long, 2 feet 

 wide, and 15 inches deep. Water, which is first filtered through crushed 

 rock, is supplied to the box by four 1-inch diameter aluminum conduit 

 pipes placed full length in the bottom of the box. Use of such a device for 

 anadromous fish permits the incubation of eggs in the stream system in 

 which the fish are to be released. 



A similar type of system involves incubation channels. Incubation chan- 

 nels differ from previously discussed spawning channels in that eyed eggs 

 are placed in prepared trenches. Fish reared under these conditions are 

 generally hardier than those reared in the hatchery. 



Plastic substrates can be added to incubation units (such as vertical 

 incubators) to simulate the environment provided by gravel. Plastic sub- 

 strate fabricated from artificial grass also has been used successfully in sal- 

 monid incubation systems to provide a more natural environment for newly 

 hatched fry and has resulted in larger and more hardy fish. 



The state of Washington has developed a method for incubating salmon 

 eggs utilizing specially designed trays placed in raceways. These units are 



Figure 70. Salmon eggs being measured into a vertical- tray incubator. A screen 

 lid is placed on top of the tray to prevent loss of eggs and hatched fry. 



