Commonwealth Responds to New Zealand Mudsnail Invasion

New Zealand MudsnailBy Michal Maňas - Maňas M. (2014). "Photo of the day (35): Potamopyrgus antipodarum". Blog about gastropods., CC BY 4.0,

PENNSYLVANIA — The Pennsylvania Fish and Boat Commission (PFBC) recently announced that the Benner Spring and Pleasant Gap State Fish Hatcheries (SFHs), both located in Centre County, are operating under a special response plan following the detection of invasive New Zealand Mudsnails on hatchery premises.

During a scheduled staff training at Benner Spring SFH on May 31, 2022, New Zealand Mudsnails were detected within water supply plumbing inside a hatchery building.  It is important to note that while this is the first detection of New Zealand Mudsnails in a PFBC hatchery, these snails are known to have been present since 2010 in Spring Creek, Centre County, which is adjacent to the Benner Spring facility.

The discovery at Benner Spring SFH prompted the PFBC to immediately activate the New Zealand Mudsnail Prevention, Monitoring, and Response Plan, which included suspending all transfers of fish into and out of Benner Spring until further notice.  Additionally, more thorough inspections were scheduled at Benner Spring and all other state fish hatcheries and cooperative nurseries across Pennsylvania that are connected to or near waters that are known to contain New Zealand Mudsnails.  During this process, New Zealand Mudsnails were detected at the Pleasant Gap SFH, which is adjacent to the Logan Branch of Spring Creek, a water also known to contain the invasive snails.  Inspections at all other SFHs were negative.  Four cooperative nurseries operated by volunteer conservation organizations in Northampton, Lehigh, and Franklin counties, were found to contain New Zealand Mudsnails.

While New Zealand Mudsnails were not detected in areas of the Benner Spring and Pleasant Gap SFHs which contained fish, under the response plan, immediate action was taken to enhance biosecurity measures at all SFHs and conduct a high-level risk assessment.  Actions included the installation, repair, or replacement of bird netting over fish raceways; installation of additional freezers at the hatcheries to be used for the disinfection of waders; and installation of additional electrical barriers around hatchery facilities to prevent snail movement into the hatcheries.  Large-scale disinfection operations were conducted at Benner Spring and Pleasant Gap SFHs that included the cleaning and drying of raceways using high-pressure and high-temperature steam, and the use of propane torches to burn any organic material within the raceways.  Quarantine zones were established within the hatchery raceways for the monitoring of groups of fish, and sampling of fish digestive material was conducted on hundreds of fish to detect any presence of New Zealand Mudsnails.

While continuing to follow these strict operational protocols for several months, there have been several additional detections of New Zealand Mudsnails at Benner Spring and Pleasant Gap SFHs, although no snails have ever been detected among the fish populations or within the digestive systems of any fish.  While disinfection, inspection, and quarantine operations will continue to be conducted at affected SFHs indefinitely as part of the ongoing risk assessment process, trout from the Benner Spring and Pleasant Gap SFHs were deemed to be unaffected by the presence of New Zealand Mudsnails at the hatcheries.  Throughout spring and summer 2022, staff from the PFBC Division of Fisheries Management conducted New Zealand Mudsnail surveys on select waters that had been stocked with trout from the Benner Spring and Pleasant Gap SFHs prior to the detection at the hatcheries in May 2022, and no snails were found.  In October 2022, several thousand fish were removed from quarantine at the affected hatcheries and were approved for use in the PFBC’s fall and winter trout stocking operations.

The PFBC continues to work with operators of the cooperative nurseries which were found to contain New Zealand Mudsnails.  Thorough inspections, disinfection, and risk assessment processes will continue indefinitely to determine the appropriate use of the fish for stocking operations.

Along with enhanced biosecurity measures now in place, PFBC staff have, for many years, taken measures to prevent the spread of New Zealand Mudsnails, including frequent disinfection of hatchery gear and stocking equipment, and the installation of electrical barriers where waters enter and exit the hatcheries to prevent the movement of snails into the facilities.  The PFBC has consulted with a hydrogeologist to investigate water sources at the affected SFHs and determine if alternative water sources can be utilized to further prevent the spread of New Zealand Mudsnails into the facilities.

The PFBC also encourages anglers and boaters to inspect and disinfect their gear in between each trip, especially when moving from one water to another.  Tips for disinfecting your gear can be found on the PFBC website (

New Zealand Mudsnails have been documented in approximately 30 waters across Pennsylvania, including several popular cold-water trout fisheries in central and eastern Pennsylvania.  Roughly the size of a match head or even smaller, these snails are spread to new waters by attaching to waders, fishing gear, and boats, and have the potential to reach densities of hundreds or even thousands of snails per square foot of a streambed.  New Zealand Mudsnails are not harmful to humans but can compete with and negatively impact native freshwater invertebrate species, such as other snails and aquatic insects.

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