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.