Flavobacterium psychrophilum in Baltic salmon Salmo salar brood fish and their offspring

Baltic salmon brood fish were investigated for the presence of Flavobacteri um psychrophilum in the kidney, spleen, brain and sexual products (ovarian fluid, unfertilised eggs and milt). Samples for bacteriology were taken at capture, when the fish were ascending their native river to spawn, and afte r a period of captivity in indoor pools, at stripping. During captivity, ab normal wiggling behaviour was recorded in some of the fish. Bacterial sampl es were taken to determine if F. psychrophilum had any role in the aetiolog y of the condition. Furthermore, the presence of F. psychrophilum on egg su rfaces during incubation was investigated. F. psychrophilum was isolated fr om internal organs and/or sexual products in 7 out of 50 (14.0%) fish sampl ed at capture and 63 out of 272 (23.2%) fish sampled at stripping. The bact eria was isolated from either spleen or gonads in 2 out of 19 (10.5%) fish with abnormal wiggling behaviour but no bacteria was isolated from the brai n. No F. psychrophilum was isolated from eggs at the eyed stage. Just befor e hatching, the bacterium was isolated from 5 out of 15 (33.3%) family grou ps. The present study shows that Baltic salmon brood fish are carriers of F . psychrophilum during their spawning migration. The presence of the bacter ia in sexual products from both females and males indicates that transmissi on from the brood fish to the offspring should be considered an important r oute of infection.