Pathogens and Biological Control of Invasive Silver Carp (Hypophthalmichthys molitrix) and Bighead Carp (H. nobilis)

Aquatic invasive species threaten ecosystems and biodiversity through competition, predation, habitat alteration and pathogen introductions. Bigheaded carps (BHC), including silver, Hypophthalmichthys molitrix Valenciennes, and bighead, H. nobilis Richardson, carps, are prolific, invasive pests in central US rivers and pose a substantial threat to Great Lakes fisheries. Little is known about the effect of pathogens on invading BHC or how BHC affect the disease risk profile for native fishes in receiving ecosystems. We therefore conducted a systematic survey of pathogens for BHC and native fishes in the Wabash and Tippecanoe rivers, Indiana, USA. We found Pseudomonas fluorescens, P. putida, and Salmonella enterica DNA in BHC. All of these bacteria are pathogenic to fishes, but not exclusively pathogenic to carps. No gastrointestinal helminths were detected in BHC, although they were common in most native fishes examined. We also conducted in vitro studies on BHC tissues (skin, gill, fin, and fry) and found high sensitivity to largemouth bass virus, viral hemorrhagic septicemia virus, and infectious pancreatic necrosis virus. We conclude that BHC in the study area are not heavily burdened by exposure to pathogens in these invaded ecosystems, although they do harbor native bacteria and show potential for high sensitivity to endemic viruses.