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 before the immune system of the fish is able to mount an efficient, protective response. This study was undertaken to determine if protective antibodies could be transferred to salmonid eggs and embryos by injecting the antibodies into female broodstock salmon prior to spawning. Resistance to Vibrio anguillarum (Va) was used as the model for this system because it is known that resistance to vibriosis is antibody-mediated. 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 also challenged with Va following absorption of their yolk sac, but were not protected against Va. Contents of eggs from all broodstock (including saline-injected controls) were injected into naive coho fry, which were then challenged with live Va. Egg material from broodstock injected 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 maintained for long after the yolk sac is absorbed. The findings described demonstrate a potentially useful new approach for passively immunizing large numbers of yolk sac larval salmonids against certain pathogens.