The discovery of Clinostomum complanatum metacercariae in farmed Chinese sucker, Myxocyprinus asiaticus

Yellow grub disease is a common fish parasitosis caused by Clinostomum species. Clinostomum complanatum is a cosmopolitan trematode with a complex life-cycle and low host specificity. Due to their infectivity to humans, the metacercariae of C. complanatum are considered zoonotic trematodes. In the current study, morphological and molecular (COI and ITS) analysis of metacercariae revealed that the genital complex might be a more reliable diagnostic feature than other morphological characteristics in identifying species of Clinostomum. Phylogenetic analysis using the two gene regions confirmed the identity of the species as C. complanatum. In this study, the cultured Chinese sucker (Myxocyprinus asiaticus) was found to be a new fish host for C. complanatum. Ninety-six specimens (i.e. 64.9% of the 148 specimens examined) were infected by the parasite with the number of metacercariae ranging from 1 to 7 (mean: 2.33 ± 1.38) per host. The body weight and condition factor of infected fish was lower when compared to those of uninfected conspecifics (p < 0.001). The presence of two snails, Radix swinhoei and Galba pervia, which serve as intermediate hosts, were found breeding within the canals and waterways feeding the farm and were the source of infection.