Immunocompetence of juvenile Chinook salmon against Listonella anguillarum following dietary exposure to Aroclor 1254.

Controlled laboratory challenges with pathogenic Listonella (formerly Vibrio) anguillarum bacteria were used to examine potential effects of dietary exposure to polychlorinated biphenyls (PCBs) on the growth and immunocompetence of juvenile Puget Sound (WA, USA) Chinook salmon (Oncorhynchus tschawytscha). Salmon were fed four levels of the PCB congener mixture Aroclor 1254 for 28 d to bracket likely exposure to PCBs in the lower Duwamish waterway near Seattle, Washington, USA. Fish were transferred to five replicate tanks per dose, exposed to L. anguillarum, and monitored for 14 d. Half the PCB-dosed fish were vaccinated against L. anguillarum, and specific immunity was allowed to develop in this group for three weeks prior to challenge. All mortalities following challenge were individually sampled for bacteria to identify the cause of death. The data indicate that dietary PCB exposure, even at relatively high levels, did not have a significant effect on growth, innate disease resistance, or acquired immunity to L anguillarum. The controlled laboratory experiments in this study suggest that the immune system of Chinook salmon is not sensitive to orally delivered PCBs at environmentally relevant concentrations.

Immunocompetence of juvenile chinook salmon against Listonella anguillarum following dietary exposure to polycyclic aromatic hydrocarbons.

Juvenile chinook salmon (Oncorhynchus tschawytscha) were fed a mixture of 14 polycyclic aromatic hydrocarbon (PAH) compounds that reflected the PAH composition of salmon stomach contents in an urban estuary of Puget Sound, Washington (USA). Following a 28-d dietary exposure, a standardized Listonella anguillarum challenge model was used to determine whether PAH exposure (16, 64, and 252 mg/kg wet wt feed) causes reduced disease resistance under the conditions examined in this study. To assess innate immunity, five replicate groups of fish per dose were acclimated for one week, exposed to a lethal concentration 60 of bacteria, and monitored for 14 d. In a parallel experiment, the effects of PAH exposure on the acquired immune response were examined by immersion vaccinating fish against L. anguillarum and allowing specific immunity to develop for three weeks prior to challenge. All mortalities were aseptically sampled to confirm L. anguillarum infections. No significant differences in fish length, weight, or coefficient of condition were observed. These controlled laboratory experiments suggest that dietary exposures to an environmentally relevant mixture of PAH compounds do not alter the immunocompetence or growth of juvenile chinook salmon.