highest mortality rate is associated with the 

 1953 brood, which had the poorest return in 

 recent years (see fig. 6). 



Normally the disease makes its first appear- 

 ance shortly after the fry have hatched. Johnson 

 also reports an occasional occurrence just 

 prior to hatching but has never noted it earlier 

 in the egg stage. Yolk material has been found 

 in the body cavities long after the fish have 

 started feeding. A cause and a cure for the 

 disease have not been discovered. Delayed 

 mortality after the release of the fish has never 

 been investigated. 



Increased Crowding 



Since 1949 the rearing capacity in cubic feet 

 of the rearing space used at Spring Creek 

 Hatchery has increased less than fourfold. The 

 pounds of fingerlings reared have increased 

 over sevenfold. The available water from 

 Spring Creek has remained at a constant level 

 of 3,500 gallons per minute since 1950. The 

 result has been an increase in pounds of fish 

 reared per cubic foot of space and per gallon 

 of flow. 



For the last few brood years (not included in 

 the analysis) Columbia River water has been 

 used to increase the flow of water through the 

 raceways. This was considered necessary to 

 remove waste products and maintain proper 

 oxygen concentration during periods of high 

 fish density. In the spring of 1960 the pumps 

 supplying the river water failed for a short 

 time." An immediate effect was noticed. The 

 fish showed distress, and an increase in mor- 

 tality occurred. This mortality occurred dur- 

 ing a year when fewer pounds of fish were 

 being reared than in the 1952 and 1955 brood 

 years, and in the earlier years no additional 

 water was utilized. Though apparent mor- 

 talities in the ponds were normal for the 1952 

 and 1955 broods, the possibility of damage to 

 some of the fish resulting in delayed mortal- 

 ities cannot be overlooked. 



* From personal communication with Clyde Adams, 

 superintendent of Spring Creek Hatchery, 



Composition of Diet 



In appendix table 10 the total pounds of food 

 fed at Spring Creek Hatchery and the composi- 

 tion of diet in percent is given for the brood 

 years 1943-45. Data for earlier years are not 

 available. In order to keep yearly data on a 

 comparative basis, the data in appendix table 10 

 include only food fed during the months of 

 February through May when the hatchery was 

 almost exclusively concerned with rearing fall 

 Chinook fingerlings. In addition, appendix table 

 10 includes only the diet for fish of Spring 

 Creek Hatchery origin. 



The abrupt change in diet composition since 

 1950 is immediately apparent and was coin- 

 cident in time with reduced adult return 

 (fig. 6). In general, the change involved the 

 substitution of salmon eggs and salmon flesh 

 for melts, horsemeat, and salmon viscera, 

 though for the 1954 and 1955 broods salmon 

 viscera were restored to the diet. It is pos- 

 sible that either the elimination of important 

 components or the introduction of deleterious 

 components resulted from this change. The 

 possible infection with acid-fast bacteria by 

 feeding salmon products has been noted. Studies 

 at Leavenworth Hatchery (Robinson, Palmer, 

 and Burrows, 1951) on sockeye salmon 

 (0. nerka) indicate that no benefits were de- 

 rived from feeding a high percentage of salmon 

 eggs in the diet when water temperatures were 

 in the vicinity of 45° F. Mortalities were high, 

 and growth rate was not particularly good until 

 water temperatures increased. Burrows, 

 Palmer, Newman, and Azevedo (1952) found 

 somewhat similar effects using both sockeye 

 and Chinook salmon. 



Handling of Fry and Fingerlings 



Prior to the 1949 brood year, total numbers 

 of fish released were estimated by subtracting 

 the known mortalities from the number of fish 

 placed in the ponds after hatching, which in 

 turn had been estimated by subtracting the egg 

 mortality from the original number of eggs. 

 Before a release of fed fish was made, a 

 random sample of fish was taken and the num- 

 ber of fish per pound was determined. When 

 unfed fry were released, a constant weight of 



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