30 



CAI.irOKNIA FISH AND (UMK 



Experimental Procedure 



Construction of Gravel Beds 



Three standard hatchery troughs were each divided into seven 

 nests 16" wide and 20" long by installing \" wire screens on the 

 upstream side and \" wire screens 'in the downstream side. A space of 

 4" was left between nests. The finer mesh prevented loss of gravel or 

 passage of fish to adjacent nests while the larger mesh permitted access 

 of the emerging fry to the upstream space between nests where they 

 could be caught and counted more readily. Baffles were placed between 

 nests to force the water downward through the nests and prevent short 

 circuiting above the gravel. Figure 11 shows a cross section of one 

 trough to illustrate the arrangement more clearly, ({ravel which had 

 been secured from the San Lorenzo River bottom and freed of silt by 

 washing on an ordinary window screen was placed in the 21 nests to 

 a depth of one to two inches. 



BAFFLES 



WATER 



SCREENS 



FLOW 



\dra in 



LONGITUDINAL SECTION & PLAN SHOWING GRAVEL 

 BED ARRANGEMENT OF 

 ONE TROUGH 



Fir.. 1 1 



Spawning 



A total of 37,700 silver salmon eggs (Oncorhynchus kisittch) meas- 

 uring 198 per ounce were taken from 17 females at the San Lorenzo 

 egg collecting slut ion on January 7, 1!>41. The eggs were fertilized in 

 the usual manner and covered with water in a 10-gallon fish planting 

 can where they were allowed to harden for one hour before transpor- 

 tation to the hatchery. 



Distribution of Eggs 



The eggs were thoroughly mixed so that each experimental group 

 would be uniform in character. Groups of 500 eggs were then counted 

 and placed on the gravel in each of the 21 nests. The eggs were then 

 covered by three to four inches of similar gravel and the trough drains 

 arranged to maintain one to two inches of water above this level. In a 



