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Field Research

Sentinel mallard trials

Mallard and grass carp field studies were conducted at Davis Pond, a privately-owned pond, with no connecting tributaries, near Thurmond. Hydrilla first colonized Davis Pond in 2003 and at the beginning of this trial approximately 80% of the surface area was covered with hydrilla. Hydrilla leaves, collected from Davis Pond, were viewed microscopically and the suspect cyanobacterium covered 40 – 90% of the leaf surface. Morphological identification was confirmed using an RT-PCR) probe (Williams et al. 2007). A sentinel mallard trial Davis pond confirmed that the hydrilla-cyanobacterium complex produced AVM in these mallards (Wilde et al., 2005).

Mallard trial at Davis pond

Grass carp trials

One mitigation strategy to protect birds from the toxin associated with AVM is to eliminate aquatic plants that provide substrate for the suspect cyanobacterium. Triploid Chinese grass carp (Ctenopharyngodon idella) have been used in successful, cost-effective, and long-term vegetation control in large, man-made reservoirs, similar to those affected by AVM (Haynie 2008) In order to answer the questions regarding the potential use of grass carp to control invasive aquatic plants in systems affected by AVM we conducted a series of field and laboratory experiments. The objectives of this study were: to determine if grass carp are affected when feeding on aquatic vegetation with the suspect cyanobacterium and if these fish will function as vectors of the AVM toxin if consumed by predatory birds. No mortalities were observed and the hydrilla coverage was reduced quickly inside the enclosures due to grass carp herbivory. The initial trial indicated that grass carp could develop lesions similiar to AVM positive birds. Feeding trials with the fish, however, did not produce AVM lesions in laboratory chicken trials (Haynie 2008).

Susan and Becca studying carp

Field collected animals

In addition to the laboratory trials, researchers evaluated mammalian susceptibility using field collected animals. Neurologically impaired beavers were noted during a disease outbreak on Thurmond reservoir, but the brain results were inconclusive (Fischer et al. 2006).