Detection of pathogens and non-target species in the baitfish supply chain

The movement of live fish for use as bait in recreational angling has been identified as a high-risk pathway for the spread of aquatic invasive species and disease in the Great Lakes region. To better understand the hazards present in Minnesota’s live baitfish pathway, we employed both conventional and advanced diagnostic approaches to detect non-target species and pathogens in golden shiners (Notemigonus crysoleucas), a common baitfish sold in retail bait shops. Golden shiners were purchased from bait shops (n = 34 total; n = 15 sampled once, n = 19 sampled twice) in 2014 and 2015 across Minnesota. Of the 53 lots examined, non-target species were observed in 24/53 lots and included nine different fish species and one frog species, however, none of the non-target species found are listed as invasive in Minnesota. Nine parasite taxa were observed by wet mounts of the gills, epidermal mucus, and fin clips in 27/53 lots. The microsporidian parasite, Ovipleistophora ovariae, was detected in 24/53 lots by qPCR. While many bacterial species were identified by culture dependent and independent methods, two notable species including, Aeromonas salmonicida and Yersinia ruckeri, were confirmed in ten and five lots, respectively. Detection of replicating virus in culture was low, with only 2/53 lots positive for the golden shiner reovirus. No other viruses were detected with the standard culture-based assays; however, a total of eight novel viruses were detected by next-generation sequencing. These findings underscore the need for a proactive surveillance approach that includes advanced diagnostic tools for the detection of emerging aquatic pathogens, to better understand and manage the risks associated with the use of live baitfish.