First isolation of Flavobacterium psychrophilum from wild adult Great Lakes lake whitefish (Coregonus clupeaformis)

Abstract

Lake whitefish (Coregonus clupeaformis; LWF) is an economically and ecologically valuable native species to the Great Lakes, but recent declines in their recruitment have generated significant concern about their future viability. Although studies have sought to identify factors contributing to declining recruitment, the potential role(s) of infectious diseases has not been thoroughly investigated. In 2018 and 2019, adult LWF were collected from Lakes Superior, Michigan, and Huron for clinical examination and bacteriological analyses. Herein, we describe the first isolation of Flavobacterium psychrophilum, aetiological agent of bacterial coldwater disease (BCWD) and rainbow trout fry syndrome (RTFS), from systemically infected adult LWF. Bacterial isolates were yellow‐orange, Gram‐negative, filamentous bacilli that were oxidase and catalase positive, and produced a flexirubin‐type pigment in 3% potassium hydroxide. Isolate identity was confirmed via F. psychrophilum‐specific PCR, and multilocus sequence typing revealed three new singleton sequence types (STs) that were distinct from all previously described F. psychrophilum STs. The prevalence of F. psychrophilum infections was 3.3, 1.7, and 0.0% in Lakes Superior, Michigan and Huron respectively. Findings illustrate the potential for F. psychrophilum to cause systemic infections in adult LWF and highlight the need for future studies to investigate the bacterium's potential role in declining LWF recruitment.

Persistence of heterologous Flavobacterium psychrophilum genetic variants in microcosms simulating fish farm and hatchery environments

“…Although F. psychrophilum has been recovered from wild/feral fish (Harrison et al, 2022; Knupp et al, 2019; Van Vliet et al, 2016), most BCWD epizootics occur in fish farms and hatcheries (Avendaño‐Herrera et al, 2014; Knupp et al, 2019; Kum et al, 2008; Li et al, 2021; Nilsen et al, 2011). Indeed, the artificial rearing environment is believed to be ideal for F. psychrophilum , as fish are reared at elevated densities, providing enhanced opportunity for horizontal transmission (Kennedy et al, 2015).…”