the feed had, on many occasions, been used at 

 hatcheries in which the epizootic did not appear. 

 It was common to have diseased fish in a trough 

 adjacent to a trough of healthy fish though both 

 were fed the same food preparation . Although 

 attempts to transmit the etiologic agent to other 

 species of fish had failed, it is possible that the 

 other species, as well as the sockeye adults, 

 were acting as carriers of the infection. 



In 1954 a large-scale experiment was 

 undertaken at the two Federal hatcheries at 

 Winthrop and Leavenworth, Washington, in an 

 effort to determine the exact method of entry of 

 the infection into the sockeye fingerling popula- 

 tions. 



Even the men working at the hatcheries were 

 divided into two groups on the basis of which 

 side of the hatcheries they worked on -- cross- 

 ing over from one side to the other was prohibited. 

 Additional labor was hired so that this division 

 could be maintained during weekends and holidays. 

 Tourists and visitors were conducted through the 

 hatchery rather than being allowed to roam and, 

 at the Leavenworth station, special troughs were 

 established near the main entrance to confine the 

 tours to as small an area as possible. Personnel 

 from other hatcheries were not allowed to enter 

 either the hatchery proper or the feed rooms. 

 The handles of all equipment were color -coded 

 and separate equipment was used for infected 

 ponds and troughs . 



EXPERIMENTAL PROCEDURE 



General hatchery procedure 



Each of the two stations, Leavenworth 

 and Winthrop, reared native fish as well as 

 some which had been spawned at the other hatch- 

 ery and, in addition, the Leavenworth station 

 reared a group of fingerlings spawned at the 

 Entiat station . Special arrangements were made 

 to obtain the frozen salmon viscera on an in- 

 dividual species basis to determine if the sockeye 

 viscera alone were the carriers of the virus or 

 whether other species could transmit the infec- 

 tion (table 1). In addition to the viscera diets, 

 one diet contained silver salmon eggs as the fish 

 component and two diets had no fresh or frozen 

 fish products; one was similar to the Cortland 

 6 A and the other a pelleted feed of private man- 

 ufacture which was discontinued shortly after it 

 was begun because of its inadequacy to maintain 

 the fingerlings nutritionally. 



Both the experimental fish and the controls 

 were handled as identically as possible. The two 

 groups were weighed and counted at the same 

 time, water flow was adjusted, the same amount 

 of feed was given at the same time of the day, 

 and the groups were moved to new troughs or into 

 the ponds simultaneously. 



In the spring, fish at the Leavenworth 

 station had an outbreak of bacterial gill disease 

 which was treated as it occurred. In general, 

 the experimental fish and their controls were 

 treated identically, but one portion of the hatchery 

 was allowed to go untreated so that any effects of 

 the treatment on the virus disease could be de- 

 tected. After the fish had been placed in the 

 outside rearing ponds they were given weekly 

 prophylactic treatments to prevent the occurrence 

 of the gill infection. Kidney disease was detected 

 early in the year at the Winthrop hatchery but 

 since the mortalities from this disease were low, 

 no treatment was administered. 



Maximum sanitary precautions were 

 taken at both stations . Feeding and cleaning 

 protocol was established on the assumption that 

 all viscera were virus contaminated. Solutions 

 of disinfectant and Live steam were used liber- 

 ally throughout the year and separate cleaning 

 and feeding equipment was used for each trough 

 and set of ponds . As an added precaution, the 

 hatcheries themselves were divided into two sec- 

 tiohs, viz: "clean" and "contaminated" by the 

 use of two feed -preparation rooms (at Leaven- 

 worth only) and by division of the hatchery troughs 

 and ponds into two, physically distinct units . 



Leavenworth hatchery 



Eggs taken at Lake Wenatchee for the 

 Leavenworth station were spawned in groups of 

 12 females (about 24,000 eggs per g^oup), hatched, 

 and the fry reared. Representative samples of 

 each group of eggs were tested for virus and all 

 subsequent records of Leavenworth -reared finger- 

 lings were maintained so that any infected troug^h 

 or pond could be traced back to the oiri^i"?'! group 

 of females from which it was obtained. No similar 

 grouping was done with the eggs received from 

 Winthrop and Entiat . After the eggs had hatched, 



