Presence and significance of chytrid fungus Batrachochytrium dendrobatidis and other amphibian pathogens at warm-water fish hatcheries in southeastern North America
Amphibian populations and species are declining or disappearing from many regions throughout the world (Stuart et al. 2004). No single cause has been demonstrated, although a number of emerging infectious diseases have been suggested as primary etiologic agents (Berger et al. 1998; Daszak et al. 2003; Lips et al. 2006). Several factors, including climate change, parasite infestation or compromised immune systems may interact locally or regionally to threaten species and populations (Carey and Bryant 1995; Parris and Beaudoin 2004; Pounds et al. 2006). Still, the disease model of amphibian decline may not be universally applicable (Daszak et al. 2005; McCallum 2005). The impacts of disease can devastate anuran populations, and declines due to disease, particularly amphibian chytrid fungus (Batrachochytrium dendrobatidis, “BD”) and ranaviruses (Berger et al. 1998; Chinchar 2002), are well documented (Daszak et al. 2003; Kiesecker et al. 2004). In addition to the better-known fungi and viruses, an undescribed Perkinsus-like organism also has had serious localized effects on populations of ranid frogs in southeastern North America (e.g. Rana sevosa in Mississippi, various Florida species; unpublished data). In North America, warm water fish hatcheries supply stock for sport fishing, ecological restoration, and endangered species management. Several million fish may be transported across multiple regions and river drainages in a single restocking event. For example, in 2004 three million bluegill (Lepomis macrochirus), originating from Orangeburg National Fish Hatchery (NFH), South Carolina were stocked at Harris Neck National Wildlife Refuge (NWR), Georgia as food for a nesting colony of endangered wood storks. This stocking in 2004 transported fish from the upper coastal plain across the Savannah River to the lower coastal plain, and may be responsible for mixing different larval phenotypes of Rana catesbeiana at Harris Neck (Dodd and Barichivich 2007). Our objective was to determine whether diseases known to have detrimental effects on amphibians (ranavirus, BD, mesomycetozoa, protozoa and helminths) are present in amphibian larvae living in warm-water fish hatcheries in the southeastern United States. We further examined hatchery records to assess the extent to which amphibian larvae have been transported throughout various regions and potentially contribute to spreading emerging infectious diseases.