The Asian fish tapeworm Schyzocotyle acheilognathi is widespread in baitfish retail stores in Michigan, USA

Background: The Asian fish tapeworm Schyzocotyle acheilognathi (Yamaguti, 1934) is an important fish pathogen because of its wide range of intermediate and definitive hosts and its pathological consequences. This study was designed to determine if baitfish are a likely vector contributing to the expansion of the invasive Asian fish tapeworm. Results: We collected live baitfish for examination from 78 retail stores in Michigan between September 2015 and June 2016. A total of 5400 baitfish (90 lots, 60 fish/ lot) were examined, including 42 emerald shiners [Notropis atherinoides (Rafinesque, 1818)] lots, 30 fathead minnow [Pimephales promelas (Rafinesque, 1820)] lots, 11 golden shiners [Notemigonus crysoleucas (Mitchill, 1814)] lots, 3 sand shiners [Notropis stramineus (Cope, 1865)] lots, 1 lot each of spottail shiners [Notropis hudsonius (Clinton, 1824)], Northern redbelly dace [Phoxinus eos (Cope, 1861)], and blacknose dace [Rhinichthys atratulus (Hermann, 1804)] and 1 lot of mixed two species: weed shiners [Notropis texanus (Girard, 1856)] and sand shiners. Conclusions: Based on its scolex and strobilar morphology combined with gene sequence analysis, S. acheilognathi was only found in emerald shiners, golden shiners and sand shiners. The mean within lot prevalence and abundance of infection was highest in emerald shiners (20.3 +/- 14.0 and 1.15 +/- 1.34), followed by golden shiners (8.3 +/- 10.7 and 0.89 +/- 1.27) and sand shiners (1.3 +/- 2.6 and 0.02 +/- 0.05). However, the mean intensity of S. acheilognathi in emerald shiners was lower (4.3 +/- 2.6) than that of golden shiners (6.6 +/- 6.7). S. acheilognathi-infected fish exhibited enlargement of the abdomen, distension of the intestinal wall, and intestinal occlusion and hemorrhage. This finding suggests that live baitfish are a likely vector by which the invasive Asian tapeworm's range is expanding.