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Diseases of Aquatic Organisms

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DAO 60:31-39 (2004)  -  doi:10.3354/dao060031

Impact of PCB on resistance to Flavobacterium psychrophilum after experimental infection of rainbow trout Oncorhynchus mykiss eggs by nanoinjection

Elisabet Ekman1,*, Gun Åkerman2, Lennart Balk2, Leif Norrgren1

1Swedish University of Agricultural Sciences (SLU), Department of Biomedical Sciences and Veterinary Public Health, Division of Pathology, Pharmacology and Toxicology, PO Box 7028, 750 07 Uppsala, Sweden
2Stockholm University, Institute of Applied Environmental Research (ITM), Laboratory for Aquatic Ecotoxicology, 106 91 Stockholm, Sweden

ABSTRACT: The effects of sublethal exposure of a commercial blend of polychlorinated biphenyls (PCB), i.e. Clophen A50, on disease resistance to the aetiological agent of rainbow trout fry syndrome, Flavobacterium psychrophilum, were investigated. Newly fertilised rainbow trout Oncorhynchus mykiss eggs were nanoinjected with 2 doses of Clophen A50 (0.4 or 2 µg egg-1) and/or 100 colony forming units of F. psychrophilum. The mean cumulative mortality in control groups, and groups exposed to the lower dose of Clophen A50 (0.4 µg egg-1) was below 5.0%. The mean cumulative mortality in groups exposed to the higher dose of Clophen A50 (2.0 µg egg-1) was 5.8%, which was not significantly different from the control groups. In all groups infected with F. psychrophilum, with or without exposure to Clophen A50, significantly higher cumulative mortalities compared with control groups were recorded. No differences in mortality were recorded between groups exposed to bacteria alone or bacteria in combination with the higher dose of Clophen A50 (21.6 and 20.4%, respectively). Decreased disease resistance was recorded in groups exposed to F. psychrophilum and the lower dose of Clophen A50, with a mean cumulative mortality of 56.0%. These results could be due to non dose-dependent effects on the immune system, or toxic effects of PCB or their metabolites on the bacteria in groups exposed to the higher dose of Clophen A50. The present study indicates that maternal transfer of PCB might affect disease resistance to vertically transmitted F. psychrophilum.

KEY WORDS: Flavobacterium psychrophilum · Rainbow trout fry syndrome · RTFS · Polychlorinated biphenyls · PCB · Disease resistance · Nanoinjection · Rainbow trout

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