1,000 fish per pound was assumed. In this way 

 handling was reduced to a minimum. The 

 present hatchery policy, however, requires 

 that all fish be weighed at time of release. 



Fingerlings are weighed by being crowded 

 into a confined area and dipped out of the ponds 

 into a weighing basket submerged in the water. 

 The weighing basket is then removed from the 

 water, most of the water is allowed to drain 

 from the basket in order to obtain an accurate 

 weight. At this time the fish are subjected to 

 the hazards of pressure and abrasion. 



Fry are usually released directly from the 

 egg trays. The egg trays are collected and 

 weighed. The total weight of fry is obtained 

 by subtracting the weight for each tray from 

 the total weight of fry plus tray. This handling 

 involves little more than is necessary to re- 

 move the fish from the tray. After the fish are 

 weighed, both fry and fingerlings are released 

 through a long hose which extends from the 

 hatching room or the ponds directly into the 

 river. 



Some question may be raised as to the 

 probable effect on accuracy of the change since 

 1949 in evaluating pounds of fingerlings re- 

 leased. Estimating numbers released by sub- 

 tracting only the observed mortalities should 

 result in an overestimate of numbers and 

 pounds released in the earlier years. As a 

 result, the return per pound of fish released 

 should be even higher for the earlier years 

 than is indicated by figure 7. 



TEMPERATURE EFFECTS 



Water temperature plays an important role 

 in fish cultural operations. Two possible ef- 

 fects of temperature are discussed in the fol- 

 lowing sections: The effect of temperature 

 during the egg and early fry stage and the 

 effect of temperature differentials between 

 Spring Creek and Columbia River at time of 

 release. It should be pointed out that the source 

 of water for the Spring Creek Hatchery is a 

 spring with a constant temperature of 46° F. 

 In the last few years, this constant tempera- 

 ture has been altered somewhat by the intro- 

 duction of Columbia River water during the 

 rearing period. 



Egg and Early Fry Stage 



Seymour (1956) conducted experiments on 

 Chinook salmon over a wide range of constant 

 temperatures. The results of 2 years' experi- 

 ments indicated that the overall mortality 

 (from the time the egg was fertilized to after 

 the resulting fish started feeding) was lowest 

 at about 45° F. Mortality increased rapidly 

 above 50° F. and below 40° F. "Abnormality" 

 was lowest among fish reared at a constant 

 temperature between 45° and 50° F. Seymour 

 also made counts of meristic characteristics 

 (vertebrae and dorsal and anal fin ray counts) 

 of fish held at the constant temperatures. 

 Plots of these counts relative to the tempera- 

 ture showed turning points in the curve in the 

 vicinity of 45° and 50° F. Seymour states in 

 his abstract that "taking into consideration 

 both mortality and growth rate, the optimum 

 temperature was about 52° F. for eggs and 

 58° F. for finger ling." 



Disregarding the effect on growth, the opti- 

 mum temperature found by Seymour for egg and 

 early fry stage appears to be very close to the 

 Spring Creek temperature. Insofar as the basic 

 structure of the organism, both physiologically 

 and anatomically, is developed during egg and 

 early fry stages, the constant temperature of 

 46° F. at Spring Creek may be an important 

 factor in the eventual survival rate of the fish. 



Temperature Differential at Time of Release 



Several workers have described the effect on 

 salmon of sudden emersion from warmer to 

 colder water. Varma (1950) subjected silver 

 salmon (0. kisutch) to a sudden transfer from 

 water of 58° F. to water of 35° F. These fish 

 were between 3 and 4 inches in length, and had 

 not been fed for 1 day prior to the experiment. 

 In the experiment an initial shock marked by 

 a loss of equilibrium by the fish was quite 

 pronounced within 10 minutes. By this time 

 the fish seemed to be "paralyzed" and the 

 respiration rate seemed to be irregular. Death 

 did not occur until the fourth day. By the 10th 

 day 4 of the 12 fish used were dead and the 

 remaining 8 were in "bad shape". 



Brett (1952) conducted experiments on 

 temperature tolerance of all five species of 



15 



