Morphological and genetic characterisation of the introduced copepod Lernaea cyprinacea Linnaeus (Cyclopoida: Lernaeidae) occurring in the Murrumbidgee catchment, Australia

Lernaea is a genus of freshwater parasitic copepod, consisting of around 80 species. The anchor worm (L. cyprinacea) is the most well-known species because of its wide distribution beyond its native range and significant effect on freshwater host species. In Australia, nearly all reported Lernaea infections are referred to as L. cyprinacea without molecular evidence. Identification solely based on morphological features is not reliable due to the highly variable morphology of Lernaea species, especially of the most important characteristic, the anchor. In Australia, the species has now been found on many native fish, including in the Murrumbidgee catchment area, which is home to several endangered species. To provide clear identification of Lernaea species, we sampled Lernaea from six fish species from various localities in the Murrumbidgee catchment, south-eastern Australia. The Lernaea specimens were described using combined traditional morphological observation and three gene regions. Although significant morphological variations were found, limited genetic differences in all three gene regions suggested they all belong to one species. Phylogenetic analyses of all tested species and those reported from other parts of the world suggested our specimens are L. cyprinacea. This study provides strong evidence for the occurrence of an introduced invasive species in Australia.