6 research outputs found
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Cumulative Effects of Natural and Anthropogenic Stress on Immune Function and Disease Resistance in Juvenile Chinook Salmon
Previous studies have shown that juvenile chinook salmon Oncorhynchus tshawytscha exposed in the field or the laboratory to polychlorinated biphenyls (PCBs), an anthropogenic stressor, are immunosuppressed. It is not known whether simultaneous exposure to natural stressors can increase this immunosuppression. To examine the effects of natural and anthropogenic stressors on immune function, we infected juvenile chinook salmon with metacercariae of the trematode Nanophyetus salmincola by exposing the fish to infected freshwater snails Juga plicifera. Infected (>300 metacercariae per fish) and noninfected salmon were then injected with either the commercial PCB mixture Aroclor 1254 or an acetone-emulphor carrier. B cell function was examined by in vitro hemolytic plaque-forming cell (PFC) assay. Nanophyetus salmincola infection resulted in significantly lower anterior kidney primary PFCs and lower splenic secondary PFCs. The combination of N. salmincola infection and Aroclor 1254 exposure caused a lower anterior kidney primary PFC response than did either stressor alone. The immune function of juvenile chinook salmon was also measured by challenging them with the marine bacterium Listonella anguillarum (formerly known as Vibrio anguillarum). Fish infected with N. salmincola had higher mortalities than noninfected fish when challenged with L. anguillarum. These experiments demonstrated that N. salmincola infection in juvenile chinook salmon can impair immune function and disease resistance. The findings also show that in combination these natural and anthropogenic stressors can have a greater negative effect on salmon health than either stressor alone.Keywords: stress, Oncorhynchus tshawytscha, polychlorinated biphenyls, immunosuppressio
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Increased Susceptibility of Juvenile Chinook Salmon to Vibriosis after Exposure to Chlorinated and Aromatic Compounds Found in Contaminated Urban Estuaries
Saltwater-adapted juvenile chinook salmon Oncorhynchus tshawytscha exposed to aromatic and chlorinated compounds, representative of contaminants found in urban estuaries in Puget Sound, have a higher susceptibility to vibriosis than do fish exposed only to the solvent vehicle. Susceptibility to vibriosis was assessed by examining the percent cumulative mortality of the salmon after exposure to the bacterial pathogen Vibrio anguillarum. The aromatic and chlorinated compounds examined consisted of a sediment extract from the Hylebos Waterway that was enriched in butadienelike compounds (chlorinated-enriched Hylebos Waterway sediment extract [CHWSE]), a model mixture of polycyclic aromatic hydrocarbons (PAHs), a polychlorinated biphenyl mixture (Aroclor 1254), hexachlorobutadiene (HCBD), and 7,12-dimethylbenz[a]anthracene (DMBA). Two trials were conducted. In trial l, the percent cumulative mortality of juvenile chinook salmon exposed to V. anguillarum after receiving either CHWSE, HCBD, or the model mixture of PAHs ranged from 28% to 31% compared with the 16% observed in the acetone:emulphor control group at 7 d post-bacterial challenge. In trial 2, the net cumulative mortality of juvenile chinook salmon exposed to V. anguillarum after receiving either DMBA or Aroclor 1254 ranged from 46% to 49% compared with the 25% observed in the acetone:emulphor control group at 9 d postchallenge. The differences in mortality between groups of fish in the treated and control groups in both trials were significant at P 0.05. These findings suggest that a higher predisposition to infection and subsequent disease can occur in salmon exposed to chemical contaminants found in urban estuaries of Puget Sound, WashingtonKeywords: polychlorinated-biphenyls, juveniles, Vibriosis, Oncorhynchus tshawytscha, estuarie
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Survey of Pathogens in Juvenile Salmon Oncorhynchus Spp. Migrating through Pacific Northwest Estuaries
Although the adverse impact of pathogens on salmon populations in the Pacific Northwest is often discussed and recognized, little is currently known regarding the incidence and corresponding significance of delayed disease-induced mortalities. In the study reported herein, we surveyed the presence and prevalence of selected micro- and macroparasites in out-migrant juvenile coho salmon Oncorhynchus kisutch and Chinook salmon O. tshawytscha from 12 coastal estuaries in the Pacific Northwest over a 6-year period (1996-2001). The major finding of this study was the widespread occurrence of pathogens in wild salmon from Pacific Northwest estuaries. The six most prevalent pathogens infecting both juvenile Chinook and coho salmon were Renibacterium salmoninarum, Nanophyetus salmincola, an erythrocytic cytoplasmic virus (erythrocytic inclusion body syndrome or erythrocytic necrosis virus), and three gram-negative bacteria (Listonella anguillarum, Yersinia ruckeri, and Aeromonas salmonicida). The most prevalent pathogen in both Chinook and coho salmon was N. salmincola, followed by the pathogens R. salmoninarum and the erythrocytic cytoplasmic virus. Statistically significant differences in the prevalence of R.. salmoninarum and N. salmincola were observed between Chinook and coho salmon. Based on the prevalence of pathogens observed in this study, disease appears to be a potentially significant factor governing the population numbers of salmon in the Pacific Northwest. Development of a detailed understanding of the principal components influencing the ecology of infectious disease will aid in the development of management and control strategies to mitigate disease in and hence further the recovery of salmon stocks listed under the Endangered Species Act