Effect of Nanophyetus salmincola and Bacterial Co‐Infection on Mortality of Juvenile Chinook Salmon

Abstract

The freshwater trematode Nanophyetus salmincola has been demonstrated to impair salmonid immune function and resistance to the marine pathogen Vibrio anguillarum, potentially resulting in ocean mortality. We examined whether infection by the parasite N. salmincola similarly increases mortality of juvenile Chinook Salmon Oncorhynchus tshawytscha when they are exposed to the freshwater pathogens Flavobacterium columnare or Aeromonas salmonicida, two bacteria that juvenile salmonids might encounter during their migration to the marine environment. We used a two-part experimental design where juvenile Chinook Salmon were first infected with N. salmincola through cohabitation with infected freshwater snails, Juga spp., and then challenged with either F. columnare or A. salmonicida. Cumulative percent mortality from F. columnare infection was higher in N. salmincola-parasitized fish than in nonparasitized fish. In contrast, cumulative percent mortality from A. salmonicida infection did not differ between N. salmincola-parasitized and nonparasitized groups. No mortalities were observed in the N. salmincola-parasitized-only and control groups from either challenge. Our study demonstrates that a relatively high mean intensity (>200 metacercariae per posterior kidney) of encysted N. salmincola metacercariae can alter the outcomes of bacterial infection in juvenile Chinook Salmon, which might have implications for disease in wild fish populations.

Infection by Nanophyetus salmincola and Toxic Contaminant Exposure in Out‐migrating Steelhead from Puget Sound, Washington: Implications for Early Marine Survival

“…; Roon et al. ) and to PBDE levels comparable with those we observed in fish from the Nisqually River (Arkoosh et al. , ), potentially lowering their EMS.…”

“…salmincola infection intensity that is greater than 200 MPK is sufficient to lower the resistance of Chinook Salmon to the common bacterial pathogen, Flavobacterium columnare (Roon et al. ).…”

“…() and Roon et al. (). The posterior half of each kidney was placed in a labeled, plastic Whirlpak sample bag (60 mL) and frozen at −20°C until later enumeration of metacercariae.…”

“…Nanophyetus salmincola can reduce the resistance of Chinook Salmon O. tshawytscha to Flavobacterium columnare (Roon et al. ) and Vibrio anguillarum (Jacobsen et al. ), two pathogenic bacteria that would be encountered by steelhead in freshwater and salt water.…”

The nature and consequences of co‐infections in tilapia: A review

“…Despite the robustness of tilapia, outbreaks of diseases, particularly of bacterial origin, remain one of the main limiting factors that threaten tilapia production, specifically when cultured under intensive conditions (El‐Sayed, 2019). Fish diseases often occur following an initial stressor, and in the case of infectious disease, it is common that more than one pathogen can be identified (Kotob, Menanteau‐Ledouble, Kumar, Abdelzaher, & El‐Matbouli, 2017; Mustafa, Speare, Daley, Conboy, & Burka, 2000; Roon, Alexander, Jacobson, & Bartholomew, 2015; Zhang, Li, Chi, Ling, & Wang, 2015).…”