The Asian fish tapeworm (Schyzocotyle acheilognathi) discovered in Western Australia may pose a threat to the health of endemic native fishes

Abstract The Asian fish tapeworm (Schyzocotyle acheilognathi) is an important fish parasite with a wide host range that infects over 300 species of fish worldwide.Schyzocotyle acheilognathihas been reported from eastern coastal areas of Australia, but has not been previously reported in Western Australia (WA). During a control program for invasive freshwater fishes in south-western WA, a region with a unique and highly endangered freshwater fish fauna, tapeworms identified asS.acheilognathifrom their distinctive scolex morphology were found at a prevalence of 3.3% in goldfish (Carassius auratus), 37.0% in koi carp (Cyprinus carpio haematopterus) and 65.0% in eastern gambusia (Gambusia holbrooki) in a small suburban lake to the north of Perth. For molecular confirmation, the 18S ribosomal RNA gene was targeted at hypervariable V4 region. Koi carp isolates were 100% identical toS.acheilognathiisolated from varying hosts, including the red shiner (Cyprinella lutrensis) and a human sample. Sequences obtained from two eastern gambusia were identified asS.acheilognathi, but formed a discrete cluster and may represent a novel genotype. Isolates from two other eastern gambusia and two goldfish formed a distinct clade with only 91.9% similarity to previously sequenced isolates ofS.acheilognathi. This emphasizes the importance of molecular identification methods in addition to morphological identification. The presence and potential for transmission of these parasites in south-western WA may threaten the health of native fishes, which are immunologically naïve to this introduced parasite. Immediate control or containment measures should be implemented to halt the spread of these parasites.