SEROLOGICAL DIFFERENTIATION OF POPULATIONS OF SOCKEYE SALMON, 



ONCORHYNCHUS NERKA 



This is a report on the results of 

 a collaborative investigation^/ of the 

 differentiation of sockeye salmon ( Oncor- 

 hynchus nerka Walbaum) populations by 

 serological methods. The aim of the work 

 was to est ima te the potential value of 

 agglutinins found in the nonimmune serums 

 of animals (so-called "natural antibodies") 

 for detecting racial variations among 

 salmon erythrocyte antigens. Such aggluti- 

 nins have been used successfully in research 

 on the erythrocyte entigens of man, cattle, 

 sheep, chickens, and other warm-blooded 

 animals. (Cf. Cushing and Campbell 1957 

 for a general account of these reactions). 

 They have also been used to demonstrate 

 individual variations in the erythrocyte 

 antigens of skipjack Katsuwonis pelamis 

 Linnaeus (Cushing, 1956) and brown bull- 

 heads, Ictalurus n. nebulosus Le Sueur 

 (Cushing and Durall 1957 ) , and other 

 fishes, Suyehiro (19^9)- 



Variations in erythrocyte antigens 

 provide favorable material for racial 

 analyses, since whenever studied their 

 genetic determination has been found to 

 be simple and direct. Also their speci- 

 ficity has not been found to be subject 

 to environmental influences. Evidence 

 for the genetic determination of such 

 variations in fish has recently been pro- 

 vided by Hildeman (195b) , and the po- 

 tential utilization of these antigens in 

 fishery research has been discussed by 

 Cushing and Sprague (1953 ), and by 

 Ridgway (1957)- 



1/ This collaboration was made possible 

 through agreements reached by the U. S. 

 Fish and Wildlife Service, the Regents 

 of the University of California, and 

 the Office of Naval Research. The re- 

 search was supported in part by a con- 

 tract with the Office of Naval Research. 



MATERIALS AND METHODS 



Samples of whole salmon blood were 

 obtained by field crews from the major 

 salmon-producing rivers of North America 

 and were either shipped immediately by 

 commercial air transport or brought 

 directly to the laboratory. These samples 

 were collected by bleeding salmon from 

 the tail into open-mouth screw-cap bottles 

 without preservative or anticoagulant. 

 The largest collections were made in the 

 rivers of Bristol Bay and at various 

 localities in the Columbia River System. 

 The clotted bloods (approximately 5 to 50 

 ml.) were transported in bottles in insu- 

 lated picnic jugs containing ice. They 

 were usually received from 1 to 3 days 

 after collection and were kept refriger- 

 ated at 5 to 10°C. until used. Under these 

 conditions most of the samples remained 

 useful for a week or two. 



Suspensions (1.5 percent) of fresh 

 cells were prepared on the day of use by 

 washing 1-5 ml. aliquots of whole blood 

 in three 20-ml. changes of Alsever's 

 solution. All washings were carried out 

 in a refrigerated centrifuge , and the cell 

 suspensions were kept refrigerated except 

 when in immediate use. Individual tests 

 were performed by placing two drops of 

 suspension with two drops of suitable 

 serum dilution in 10 x 70 ml. test tubes. 

 After 15 minutes ' incubation at room 

 temperature, the tubes were centrifuged 

 for 1 minute. The sedimented cells were 

 re suspended by lightly tapping the tube 

 and the degree of agglutination was scored 

 in the conventional manner (k indicating 

 very strong, 3 strong, 2 moderate, 1 light 

 and + barely detectable agglutination with 

 indicating no agglutination). 



The influence of variables such as 

 the speed of centrifuging, age of cells, 

 temperature, etc., were considered and 

 controlled. Efforts were made to control 

 the objectivity and accuracy of the method 

 by testing the same sample on different 



