32 CALIFORNIA PISH AND GAME 



the flow of water carried silt to all seven nests of the trough. During 

 the course of the experiment the point of silt application was changed 

 to gravel nests further downstream, thus producing turbidity in the 

 lower nests for progressively longer periods, while the upper nests 

 received silt onty for the earlier stages of the incubation period. 



The above procedure was reversed for Trough 3 in which silt was 

 first applied to nest 7 and was progressively changed to upstream points 

 as the period of incubation advanced. Silting was discontinued on 

 March 20th. Thus the upper three nests did not receive silt during 

 incubation but were subjected to silt for varying portions of the early 

 emergence period. The' four lower nests received silt during the first 

 half of the emergence period and also were silted for progressively 

 longer portions of the incubation period, nest 7 receiving silt from the 

 initial day of the experiment. The period of silt addition for Troughs 

 2 and 3 may be visualized by referring to Figures 15 or 17. 



Analyses and Records 



Records were kept of water temperature, volume of flow, dissolved 

 oxygen, pH, and suspended solids. Analyses will be found in Tables 

 4 and 5. In summary, the water temperature varied from 48° to 54° 

 F. ; dissolved oxygen from 10.0 to 11.8 p. p.m., and pH from 7.4 to 7.6. 

 No appreciable difference in oxygon content was found above and below 

 the gravel nests. The water flow in the trough containing the basket 

 hatch was maintained at approximately 18 gallons per minute, while 

 the flow in the three gravel bed troughs was approximately 8 gallons 

 per minute. 



Seven analyses of the suspended solids content of overflow water 

 below the lowest nests of Troughs 2 and 3 showed an average of 

 1176 p.p.m. (Table 5). At the same time values for points 1-3 nests 

 upstream showed an average of 1330 p.p.m. The average loss per 

 nest was 83 p.p.m. While this may appear to be a high rate of deposi- 

 tion it should be remembered that silting was limited to 2-4 hours 

 daily and that a gradual decrease occurred during this period from 

 the above amount to clear hatchery water. 



As fry began to appear above the gravel they were collected, 

 counted and preserved with formaldehyde in bottles numbered to 

 correspond to the different nests. After one hundred days, when no 

 further fry appeared, the gravel was carefully removed from each nest 

 in order to count and observe the condition of eggs and fry that 

 remained in the beds. 



Experimental Results 



Yield of Fry— Basket Control 



The salmon eggs that were handled by baskets in flowing water 

 according to usual hatchery procedure hatched between February 12 

 and 14, corresponding to an incubation period of 36-38 days. The 

 yield was 79.9%. The temperature averaged 51.3° F. for the 38 days 

 to maximum hatch from which it may be calculated that 733 tempera- 

 ture units were required. 



