SPECIFIC PROTECTIVE ACTIVITY DEMONSTRATED IN EGGS OF BROODSTOCK SALMON INJECTED WITH RABBIT ANTIBODIES RAISED AGAINST A FISH PATHOGEN

Many infectious disease agents affect salmonids early in life, long be fore the immune system of the fish is able to mount an efficient, prot ective response. This study was undertaken to determine if protective antibodies could be transferred to salmonid eggs and embryos by inject ing the antibodies into female broodstock salmon prior to spawning. Re sistance to Vibrio anguillarum (Va) was used as the model for this sys tem because it is known that resistance to vibriosis is antibody-media ted. Antibodies raised against Va in rabbits were injected into female coho salmon Oncorhynchus kisutch before spawning and were detectable in the eggs by immunoassays. Fry from the injected broodstock were als o challenged with Va following absorption of their yolk sac, but were not protected against Va. Contents of eggs from all broodstock (includ ing saline-injected controls) were injected into naive coho fry, which were then challenged with live Va. Egg material from broodstock injec ted with rabbit anti-Va antibodies conferred protection against Va; in contrast, egg material from broodstock injected with saline did not. The results suggest that vertical transfer of mammalian antibodies can occur in salmonids; however, any conferred protection is not maintain ed for long after the yolk sac is absorbed. The findings described dem onstrate a potentially useful new approach for passively immunizing la rge numbers of yolk sac larval salmonids against certain pathogens.