Improved recapture rate of vaccinated sea-ranched Atlantic salmon, Salmo salar L.

Vaccination of sea-ranched Atlantic salmon was conducted in order to invest igate if immunoprophylactic measures could improve their survival. Fish wer e either vaccinated by bath or injection. A total of 66 000 fish were reare d in fresh water at a hatchery on the island of Bornholm and at the presmol t stage were separated in three groups each comprising of 22 000 fish. One group was vaccinated intraperitoneally with a polyvalent vaccine (containin g killed Vibrio anguillarum serotype O1 and O2, Yersinia ruckeri and Aeromo nas salmonicida). A second group was bath vaccinated with the corresponding vaccine-components and the third group was used as a non-vaccinated contro l. One month after vaccination these groups were allocated to three separat e net-pens located 500 m from the coastline of the island. After 4 months i n the net-pens, 1000 fish from each cage were tagged with Carlin-tags below the dorsal fin. The fish were then released for a migration period in the Baltic Sea. Following a sea period of 40 months (45 months post-vaccination ), the recapture rates of the groups were calculated from the returned tags from fishermen. Recapture of the injection vaccinated group was significan tly higher (25%) compared with the bath vaccinated fish (14.7%) and the con trol group (16.8%).