Do freshwater aquaculture facilities provide an invasion risk for zooplankton hitchhikers?

Abstract

While numerous examples exist of freshwater species from aquaculture facilities establishing non-indigenous populations following intentional release, and unintentional escape, clear links between invasions of non-target ‘hitchhiker’ species and this vector are to date are far less convincing. We examined zooplankton from nine New Zealand fish farms, including those with traditional outdoor pond systems, modern Recirculating Aquaculture Systems (RAS), and of zooplankton cultured as food for fish, to determine the prevalence of non-indigenous species among these facilities. Several non-indigenous species were found during our surveys, from all three sources, indicating that freshwater aquaculture provides invasion risks for non-native zooplankton in a variety of ways. Significantly, the North American calanoid copepod Skistodiaptomus pallidus was recorded at five farms with pond operations, greatly strengthening the link between the establishment of this species in New Zealand lakes with the release of grass carp for aquatic weed control. Traditional pond systems were commonly found to contain large populations of non-indigenous species, with risk seemingly greatest where fish are released from these operations. RAS operations contained relatively low numbers of individuals overall, suggesting a movement to this form of aquaculture from pond systems will greatly reduce the invasion risk from the freshwater aquaculture industry. We recommend a tightening of regulations regarding fish release from aquaculture ponds, following the determination of best practice methods to reduce the potential movement of hitchhiking taxa.