Transcriptional changes in innate immunity genes in head kidney associated with Aeromonus salmonicida infection in polycyclic aromatic hydrocarbon mixture-fed rainbow trout

Responses of salmonid populations to ecosystem degradation often, if not typically, involve multiple stressors. The interaction of disease and contaminant exposure is of potential relevance to persistence of salmonid populations. The duration of PAH exposure and the life stage of exposure in the trout reflect a likely exposure scenario for some stocks of anadromous salmonids (sub-yearling ocean-type Chinook salmon) during emigration to the ocean. This current study focuses on the genes expressed in rainbow trout after exposure to both the high molecular weight PAH mixture and to the A. salmonicida pathogen. Rainbow trout (Oncorhynchus mykiss) were fed a mixture of ten high molecular weight polycyclic aromatic hydrocarbons (PAH) at an environmentally relevant concentration (400ppm) for 50 days. After 50 days of PAH exposure, fish were challenged with Aeromonas salmonicida (A. Salmonicida), the causative agent of furunculosis, at a lethal concentration 30 (LC30) or growth media without the pathogen (mock challenge). There were a total of four treatment combinations: (1) mock-challenged, control-fed fish; (2) A. salmonicida-challenged, control-fed fish; (3) mock-challenged, PAH-fed fish; (4) A. salmonicida-challenged, PAH-fed fish. Head kidney was collected 2, 4, 10 and 20 days after challenge.