The Discovery of Asian Fish Tapeworm (Schyzocotyle Acheilognathi) and Schyzocotyle Sp. In Western Australia May Pose a Threat to the Health of Endemic Native Fishes

Abstract

PurposeThe Asian fish tapeworm (Schyzocotyle acheilognathi) is an important fish parasite with a wide host range that infects over 300 species of fish worldwide. Schyzocotyle acheilognathi has been reported from eastern coastal areas of Australia, but has not been previously reported in Western Australia (WA). MethodsDuring a control program for invasive freshwater fishes in south-western WA, a region with a unique and highly endangered freshwater fish fauna, tapeworms identified as S. acheilognathi from 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 mosquitofish (Gambusia holbrooki). For molecular confirmation, the 18S rRNA gene was targeted at hypervariable region V4 using conventional PCR and Sanger sequencing.ResultsKoi carp isolates were 100.0% identical to S. acheilognathi isolated from varying hosts including the red shiner (Cyprinella lutrensis) and a human sample. Sequences from two eastern mosquitofish were identified as S. acheilognathi, but formed a discrete subclass and may represent a novel genotype. Isolates from two other eastern mosquitofish and two goldfish formed a distinct clade with only 91.9% similarity to previously sequenced isolates of S. acheilognathi, indicating a potentially novel Schyzocotyle species. ConclusionThis emphasises the importance of molecular identification methods in addition to morphological identification. The presence and potential for spread 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.