Harrison

Field And Laboratory-Based Experiments Provide Evidence That Carnobacterium Infection May Be A Factor In Poor Lake Whitefish (Coregonus clupeaformis) Recruitment In The Great Lakes

1,2Courtney E. Harrison, 2Travis O. Brenden, 3Mark P. Ebener, 1,2Christopher K. Knupp, 5Isaac F. Standish,1,2Amber E. Johnston, 1,2,4Thomas P. Loch

1Michigan State University - Aquatic Animal Health Laboratory, Aquatic Animal Disease Ecology Program, East Lansing, MI; 2Department of Fisheries and Wildlife, College of Agriculture and Natural Resources, Michigan State University, East Lansing, MI; 3TFLWFC, Sault Ste. Marie, MI; 4Department of Pathobiology & Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI; 5United States Fish and Wildlife Service, La Crosse Fish Health Center, Onalaska, WI

ABSTRACT

Great Lakes lake whitefish (Coregonus clupeaformis; GL-LWF) continue to suffer from poor recruitment, yet the role infectious diseases may be playing in these declines has not been thoroughly investigated. During a multi-year study to this end, we recently detected systemic Carnobacterium (Family Carnobacteriaceae) infections in adult GL-LWF collected from Lakes Michigan and Huron and at a prevalence often higher in fish collected from sites tied to poor recruitment (e.g., Baileys Harbor, 1.6%; Alpena, 1.6 – 6.6%) compared to sites within the same lakes that are associated with good recruitment (Menominee, 0%; Saginaw Bay, 1.6 – 3.2%). Notably, Carnobacterium infections were also detected in the gonads of some spawning fish, highlighting the potential for the bacterium to be transmitted from infected parents to offspring and as occurs in other salmonid species. To elucidate the effects Carnobacterium infections may have on GL-LWF health and survival, captive-reared juveniles originating from wild artificially-spawned GL-LWF were transferred and reared under quarantine conditions in preparation for pathogen-challenge experiments. However, before Carnobacterium challenge experiments could begin, juvenile GL-LWF began to develop severe gross disease signs (e.g., severe exophthalmia and ocular hemorrhage) that was soon followed by mortality, eventually reaching ~25 – 32%. Bacterial culture and quantitative PCR analyses revealed Carnobacterium infections in the brains, eyes, kidneys, gonads, and swim-bladders of diseased fish at varying intensities. Molecular and phylogenetic analyses confirmed that bacteria isolated from diseased fish were Carnobacterium maltaromaticum. Although unplanned, this event marks the first report of Carnobacterium being linked to disease and mortality in juvenile GL-LWF, thereby highlighting the bacterium’s pathogenic potential in this fish species. Collectively, results from this study provide evidence that Carnobacterium infections can negatively affect the health of juvenile GL-LWF and thus may be a contributing factor to continued declines in recruitment.

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