Survey of Pathogens in Hatchery Chinook Salmon with Different Out‐Migration Histories through the Snake and Columbia Rivers

Abstract

The operation of the Federal Columbia River Power System (FCRPS) has negatively affected threatened and endangered salmonid populations in the Pacific Northwest. Barging Snake River spring Chinook salmon Oncorhynchus tshawytscha through the FCRPS is one effort to mitigate the effect of the hydrosystem on juvenile salmon out-migration. However, little is known about the occurrence and transmission of infectious agents in barged juvenile salmon relative to juvenile salmon that remain in-river to navigate to the ocean. We conducted a survey of hatchery-reared spring Chinook salmon at various points along their out-migration path as they left their natal hatcheries and either migrated in-river or were barged through the FCRPS. Salmon kidneys were screened by polymerase chain reaction for nine pathogens and one family of water molds. Eight pathogens were detected; the most prevalent were Renibacterium salmoninarum and infectious hematopoietic necrosis virus. Species in the family Saprolegniaceae were also commonly detected. Pathogen prevalence was significantly greater in fish that were barged through the FCRPS than in fish left to out-migrate in-river. These results suggest that the transmission of infectious agents to susceptible juvenile salmon occurs during the barging process. Therefore, management activities that reduce pathogen exposure during barging may increase the survival of juvenile Chinook salmon after they are released.

Infections by Renibacterium salmoninarum and Nanophyetus salmincola Chapin are associated with reduced growth of juvenile Chinook salmon, Oncorhynchus tshawytscha (Walbaum), in the Northeast Pacific Ocean

“…) and the prevalence reported by Van Gaest et al . () among yearling Chinook salmon from Upper Columbia River tributaries after barging. In contrast, a series of studies on R. salmoninarum conducted in the Columbia River in the 1980s (Pascho, Elliot & Achord ; Maule et al .…”

Evaluating river management during seaward migration to recover Columbia River stream-type Chinook salmon considering the variation in marine conditions

“…Spring migrating smolts are now collected and transported, primarily by barge, from the uppermost three of four lower Snake River FCRPS dams (Williams et al 2005). Transported smolts avoid most of the direct mortality of in-river migrants but experience the injuries and stresses of collection systems at the transport dam, crowding and exposure to pathogens in holding raceways and barges, and altered estuary arrival timing (Budy et al 2002;Van Gaest et al 2011). There are numerous lines of evidence that barged fish may incur additional mortality after release as a result of these stresses of collection and transport and the altered estuary arrival timing (Budy et al 2002;Schaller et al 2007;Tuomikoski et al 2011).…”

Sensitivity and specificity of histology for diagnoses of four common pathogens and detection of nontarget pathogens in adult Chinook salmon (Oncorhynchus tshawytscha) in fresh water

“…Renibacterium salmoninarum often presents as a chronic disease, and subclinical infections are prevalent in Chinook salmon throughout the fish's lifecycle. 2,3,28,45,51,52 Therefore, it would be expected that many infected Chinook salmon are asymptomatic and that many of these fish would not exhibit lesions at a histological level. There are 2 studies comparing histology to other tests for R. salmoninarum infections.…”