Brood stock segregation of spring Chinook salmon Oncorhynchus tshawytscha by use of the enzyme-linked immunosorbent assay (ELISA) and the fluorescent antibody technique (FAT) affects the prevalence and levels of Renibacterium salmoninarum infection in progeny

Abstract

A study of the effect of maternal Renlbactenum salmoninarum infection levels on the prevalence and levels of bacterial ludney disease (BKD) in progeny fish was conducted at a production salmon hatchery A total of 302 mating pairs of spring chinook salmon Oncorhyncllus tshawytscha was screened in August 1988 for R salmoninarum by an enzyme-linked immunosorbent assay (ELISA) On the b a s ~s of ELISA testing of kidney tissues from all fish and the testing of ovanan fluid samples from a subsample of the females by a direct membrane filtration fluorescent antibody technique (MF-FAT), selected egg lots were segregated into 2 groups of 30 egg lots or about 135 000 eggs each One group contained egg lots from male and female parents that had low R salmon~narum infection levels or tested negative for R salmonlnarunl (low-BKD group) and the other group contained egg lots from female parents w t h relatively high R salmoninarum infection levels and male parents with various infection levels (high-BKD group) The progeny groups were maintamed m separate reanng units supphed with untreated nver water and were monitored for R salmonlnarum by the ELISA until they were released from the hatchery in April 1990 Total mortahty of the juvenile fish was higher ( p = 0 0001) in the high-BKD group (20 %) than in the low-BKD group (10 % ) Mortality in the high-BKD group was highest after the fish were moved from nursery tanks to raceways and clinical BKD became evident in this group During the 11 mo of raceway reanng mortality in the high-BKD group was 17 O/O compared with 5 O/O for the low-BKD group An ELISA analysls of smolts lust before release showed an R salmoninarum infection rate of 85 % in the high-BKD group and 62 % in the low-BKD group Of the posltive fish 98 % in the low-BKD group and 55 in the high-BKD group had low infection levels, whereas 36 O/O in the high-BKD group and only 1 O/O in the low-BKD group had high infection levels The results of this research suggest that segregation of brood stock by the ELISA and the MF-FAT can be used to reduce the prevalence and levels of BKD in hatchery-reared sprlng chinook salmon even in locat~ons with open water supplies