Something in the water: biosecurity monitoring of ornamental fish imports using environmental DNA

The international trade in ornamental aquatic organisms represents an important vector in the spread of invasive species worldwide, but the accurate identification of imported organisms as part of a biosecurity surveillance program offers an opportunity to mitigate potential problems. Species level identification is historically conducted visually, and more recently, with the use of DNA barcoding. However, new diagnostic methods targeting extracellular environmental DNA (eDNA) can offer advantages over these approaches, being non-destructive and potentially more sensitive at low population densities of target organisms (e.g. in mixed consignments). Despite their recent introduction, techniques utilising eDNA are quickly becoming recognised as an important tool for invasion biologists and ecosystem managers. Here, we present a model for the development of a biosecurity protocol for ornamental fish identification using degraded eDNA molecules in water. We demonstrate how a DNA barcode reference library can be mined for informative short-length markers, and report repeatable and accurate detection at low densities of the target species. This study represents a framework for biosecurity agencies to develop eDNA procedures as an innovative management technique for routine surveillance of high risk imports. Future up-scaling of the method will open up prospects for long term monitoring of entire quarantine facilities for a variety of harmful species.