Infection characteristics of Diplostomum spp. metacercariae (DsMc) were analyzed in fishes from 9 major water systems of Korea. A total of 15,879 fishes in 79 species were examined by the artificial digestion method for 8 years (2013–2020). DsMc were detected in 48 (60.8%) out of 79 fish species examined. The prevalence was higher in Pseudogobio esocinus (61.5%), Squalidus chankaensis (56.9%) and Zacco platypus (44.8%). The infection intensities were 22.1, 9.4, 7.5 and 6.7 per fish infected in Hemibarbus longirostris, P. esocinus, Z. platypus, and S. chankaensis respectively. The higher prevalence was shown in fishes from Yeongsan-gang (59.3%) and the middle reaches of Seomjin-gang (48.0%), and the higher infection intensities were revealed in fishes from above 2 regions and streams in east coast (83.1, 7.5, and 11.3 per fish infected). In index fish, Z. platypus, overall prevalence was 44.8% and the higher prevalence were revealed in the middle reaches of Seomjin-gang (79.6%), Geum-gang (79.2%) and Tamjin-gang (64.7%). The susceptibility index in index fish was highest in fish from the streams in east coast (13.64), and followed by fish from the middle reaches of Seomjin-gang (7.56) and Mangyeong-gang (4.75). This study provides several novel characteristics of DsMc infection in fishes with a report of 30 new second intermediate host of Diplostomum spp. in Korea.

This article analyzed the infection characteristics of metacercariae of Metagonimus spp. (MsMc) in fish from 9 major water systems in Korea. A total of 19,568 fish in 87 species were examined over a period of 10 years (2011–2020). MsMc were detected in fish from all 44 survey areas in 9 water systems. Most of the surveyed sites showed very low and low infection levels (66.7%), while 33.3% of the areas, such as Tamjin-gang and Seomjin-gang, revealed moderate and high infection levels. High endemicity depends on the abundance of susceptible fish species, especially sweet smelt (Plecoglosus altivelis). The susceptibility index (SI) with MsMc in index fish, Zacco spp., was very low and low levels in 62.0%, moderate in 28.0%, and high in 10.0% regions. The SI was highest in the following order: Yeongam-cheon (283.8), Hoeng-cheon (192.3), Togyo-jeosuji (131.2), Deokcheon-gang (119.1), and Joyang-gang (106.3). The recent infection status of MsMc in P. altivelis was analyzed by the survey localities. In addition, except for P. altivelis, 9 fish species were highly infected with MsMc in some survey areas, including Zacco platypus, Z. koreanus, Z. temminckii, Opsariichthys uncirostris, Rhynchocypris oxycephalus, Carassius auratus, Acheilognathus rhombeus, Onchorhynchus masou, and Tribolodon hakonensis. In Korea, 74 fish species (15 families) are collectively listed as second intermediate hosts of Metagonimus spp. This review provides several novel characteristics of MsMc infection and clarifies the fish species of second intermediate host of Metagonimus spp. in this country.