ISSN (Print) 3 ISSN (Online) 7386 ORIGINAL ARTICLE Korean J Parasitol Vol. 53, No. 3: 8998, June 5 http://dx.doi.org/.337/kjp.5.53.3.89 Trematode Metacercariae in Freshwater Fish from Water Systems of Hantangang and Imjingang in Republic of Korea WoonMok Sohn, *, ByoungKuk Na, ShinHyeong Cho, SoonWon Lee 3, SeungBong Choi 3, WonSeok Seok 3 Department of Parasitology and Tropical Medicine, and Institute of Health Sciences, Gyeongsang National University School of Medicine, Jinju 6675, Korea; Division of Malaria and Parasitic Diseases, National Institute of Health, Centers for Disease Control and Prevention, Osong 36395, Korea; 3 Infection Disease Intelligence Division, Gangwon Institute of Health and Environment, Chuncheon 8, Korea Abstract: The infection status of freshwater fish with digenetic trematode metacercariae was examined in water systems of Hantangang and Imjingang (River), the Republic of Korea. A total of 877 (59 from Hantangang and 83 from Imjingang) fishes were examined by the artificial digestion methods. Clonorchis sinensis metacercariae were detected in 7 (.%) fishes (in 3 spp.) from Hantangang in Cheorwongun, Gangwondo, and (.%) fishes (in 7 spp.) from Munsancheon in Pajusi, Gyeonggido. The average densities were.9 and 35.6 per fish infected, respectively. Metagonimus spp. metacercariae were detected in 3 (5.5%) and 3 (39.9%) fishes from Hantangang and Imjingang, and their average densities were 7.5 and 9.6 per fish infected, respectively. Centrocestus armatus metacercariae were found in 6 (7.%) and 7 (.7%) fishes from Hantangang and Imjingang, and their average number per fish infected was 69 and 8, respectively. Echinostoma spp. metacercariae were detected in 5 (8.%) and 9 (33.%) fishes from Hantangang and Imjingang, and their average densities were 9.6 and 3. per fish infected, respectively. The infection status of fishes with metacercariae of Stephanoprora spp., Diplostomum spp., Clinostomum complanatum, Metorchis orientalis, and Metorchis taiwanensis were analyzed by surveyed regions. Conclusively, it was confirmed that C. sinensis metacercariae were quite commonly detected in fishes from Munsancheon but rarely from other localities, whereas the metacercariae of other digenetic trematodes were relatively prevalent in fishes from water systems of Hantangang and Imjingang in Korea. Key words: Clonorchis sinensis, Metagonimus spp., Centrocestus armatus, Echinostoma spp. and Stephanoprora spp., Diplostomum spp., freshwater fish, digenetic trematode, metacercaria, Hantangang, Imjingang INTRODUCTION Digenetic trematodes (subclass Digenea) are a relatively large group comprising of more than,5 nominal genera, and generally has 3 hosts, intermediate and definitive, in the life cycle. A variety of vertebrates, i.e., fish, amphibian, reptilian, and arthropod, act as the second intermediate hosts containing the infective larvae, metacercariae. Most of digenetic trematode metacercariae (DTM) are detected in the fish hosts, and are morphologically distinguished because they retain unique morphologies species by species [,]. In the Republic of Korea (Korea), since Chun [3] reported various DTM Received March 5, revised May 5, accepted 3 May 5. * Corresponding author (wmsohn@gnu.ac.kr) 5, Korean Society for Parasitology and Tropical Medicine This is an Open Access article distributed under the terms of the Creative Commons Attribution NonCommercial License (http://creativecommons.org/licenses/bync/3.) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. in 6 fish species collected from streams and ponds in adjacent areas of Nakdonggang ( gang means river), several workers investigated the infection status of fishes with DTM in various local areas, especially in southern Provinces, Gyeongsangdo and Jeollado []. Among the digenetic trematodes, fishborne zoonotic trematodes (FZT) provoke a public health problem in some Asian countries. FZT infections including clonorchiasis showed the higher endemicity, and they are important parasitic diseases in some riverside areas of Korea [3]. Seo et al. [] reported high prevalences of clonorchiasis and metagonimiasis among the peoples residing in the riverside areas of Korea. Cho et al. [] reported the egg positive rates in residents living in large river basins, Nakdonggang, Seomjingang, Yeongsangang, and Geumgang, located in southern parts of Korea. Recently, Kim et al. [3] surveyed the prevalence of clonorchiasis in riparian people along the 5 major rivers of Korea. On the other hand, the infection status of FZT metacercariae 89
9 Korean J Parasitol Vol. 53, No. 3: 8998, June 5 Table. Infection status of freshwater fish with trematode metacercariae by localities and fish species in Hantangang, Korea Locality andfish species examined No. of fish examined Metagonimus spp. Centrocestus armatus Echinotoma spp. Diplostomum spp % fish infected Av (range) a % fish infected Av (range) a % fish infected Av (range) a % fish infected Av (range) a Namdaecheon (Cheorwongun, Gangwondo) Acheilognathus rhombeus Coreoperca herzi Acanthorhodeus macropterus Zacco temminckii Acheilognathus koreensis Odontobutis platycephala Carassius auratus Hantangang (Cheorwongun, Gangwondo) Zacco temminckii Microphysogobio longidorsalis Acheilognathus signifer Hemibarbus mylodon Acheilognathus rhombeus Coreoperca herzi Acheilognathus lanceolatus Carassius auratus Siniperca scherzeri Sarcocheilichthys nigripinnis Hantangang (Yeoncheongun, Gyeonggido) Microphysogobio longidorsalis Hemibarbus labeo Sarcocheilichthys variegatus 8 7 5 5 5 3 3 3 35 35 6 9 5 3 69 5 7 3 35 93.3 86.7 6. 8 8 77.7. 9.3 55 6.7 7.7 6 66.7 56. 33.3 75 75 3.3 7. (3).5 (5).5 ().8 (7). (35).5 (3) 3.8 (8) 5. ().7 (3) 8.3 (5) 3 (7) 3 (37) (65) 7(6).5 (9) (7,65) 3 (68). () 7 (97) 3 83 (,65) 3. (5).7 ().3 () 5.5 (5) 93.3 66.7 9. 33.3 3..9. (3) 5.3 () 3 (788) 9 (88), (33,89),5 (595,7).6 (9),9 (5,7) (33) 88.9. 6.7 53.9. 3.7 (8) 3.9 (8) 6.3 () 3.7 (8) 6. 8. 5 7.7 5 9..3 (5) 3.8 (8) 7.3 8.6 5..8.7 (3).7 ().5 ().5 (3) 3..3.3 9. 6.3.6.9 (). (6) 8.3 (8).6 (9) 3. ().8 ().6 () (33).9.3 7..5 (). () (To be continued)
Sohn et al.: Trematode metacercariae in fish from Hantangang and Imjingang 9 Table. (Continued) Metagonimus spp. Centrocestus armatus Echinotoma spp. Diplostomum spp Locality andfish species examined % fish infected Av (range) a % fish infected Av (range) a % fish infected Av (range) a % fish infected Av (range) a No. of fish examined.9 (3) 5 59 (5,5) (9) (35).3 () 6 (9) (5) 9 (85) 76 3 6.7 85.7 39.6 5 7.5 ().7 (3).3 5 5..7 ().7 ().9.8 3.9 59 (5,5) (85) 6 Chatancheon (Yeoncheongun, Gyeonggido) Rhodeus ocellatus Coreoleuciscus splendidus Acheilognathus yamatsutae Hemibarbus labeo 39 () 9 (6) 3.3 66.7. 596 5. 6.7 9.3 9 (376) 38.9.5 (3) () 5.8 (6) 3 5 Yeongpyeongcheon (Pocheonsi, Gyeonggido) Hemibarbus labeo Cyprinus capio Zacco temminckii Pseudorasbora parva Total b 59 5.5 7.5 (,65) 7. 69 (5,7) 8. 9.6 (8) 6.7. (8) a No. of metacercariae detected (Av: average). b Total 59 freshwater fishes in species were examined. in the second intermediate hosts is used as an important epidemiological index together with those of the infection status with adult worms in the definitive and/or reservoir hosts. Thus, many Korean workers have investigated the infection status of fish from various endemic areas with FZT metacercariae to estimate the endemicities of FZT infections [3,]. Most of these studies were performed on specific trematode species, such as Clonorchis sinensis, Metagonimus spp. (including M. yokogawai), Centrocestus armatus, and Echinostoma hortense, and on the fish hosts from specific regions, such as the riverside areas of major rivers in Korea []. However, with regard to the infection status of DTM, most studies were performed before, and have not been widely conducted in freshwater fish from the water systems of Hantangang and Imjingang. Therefore, we performed the present study to investigate the infection status of freshwater fish with DTM in the water systems of Hantangang and Imjingang in Korea. MATERIALS AND METHODS Freshwater fishes examined by collection sites We collected a total of 59 freshwater fishes (in species) in 5 local sites of Hantangang, i.e., Namdaecheon ( cheon means stream) (latitude: 38.368; longitude: 7.375) in Cheorwongun, Hantangang (38.37; 7.79) in Cheorwongun, Gangwondo, Hantangang (37.9375; 7.7) in Yeoncheongun, Chatancheon (38.855; 7.76) in Yeoncheongun, and Yeongpyeongcheon (38.8; 7.88) in Pocheonsi, Gyeonggido, from August to October 3 and in June and August, (in Namdaecheon and Hantangang in Cheorwongun). The numbers and species of fish examined are presented in Table. In addition, a total of 83 freshwater fishes (in 5 species) were collected in 3 sites of Imjingang, i.e., Imjingang (38.95; 7.) in Yeoncheongun, Seokjangcheon (37.985; 6.9386) in Yeoncheongun, and Munsancheon (37.8837; 6.8563) in Pajusi, Gyeonggido, from August to October, 3. The numbers and species of fish examined are shown in Table. Examination methods All collected fishes were transferred with ice to the Department of Parasitology and Tropical Medicine, Gyeongsang National University School of Medicine, Jinju, Korea. After species identification, the fish were ground individually with a mortar with pestle or a grinder. The meat of each ground fish
9 Korean J Parasitol Vol. 53, No. 3: 8998, June 5 Table. Infection status of freshwater fish with trematode metacercariae by locality and fish species in Imjingang, Korea Locality and fish species examined No. of fish examined Metagonimus spp. Centrocestus armatus Echinotoma spp. Diplostomum spp % fish infected Av (range) a % fish infected Av (range) a % fish infected Av (range) a % fish infected Av (range) a Imjingang (Yeoncheongun, Gyeonggido) Sarcocheilichthys variegatus 7 59.3. () 3 () 3 (,5).8 (3) Acheilognathus yamatsutae 5. (6).3 () 3. (3) Abbotina springeri 5 Coreoleuciscus splendidus 9 63.7 () 6. 93 (,5) 7.7.9 (3) 5.5.8 (3) Seokjangcheon (Yeoncheongun, Gyeonggido) 8 (3) 9. 8 (83).. (8) Hemibarbus labeo 8. (6).5 ().5 () 5.5 () 3 8. 8.5 (3) 53. 8 (83) 8.8.8 () 8.8 3. (8) Munsancheon (Pajusi, Gyeonggido) 3 36.7.5 (3) 96.7 () 6.7.7 () 3 3.3.6 (5) 6 (9) 66.7 8 (8) Pseudorasbora parva 3 33.3.8 () 36.7.9 () 6.7 Odontobutis platycephala 3 96.7 () Carassius auratus Abbotina rivularis 33.3 5 () 5.7 (5) 6 6. (8) 33.3. (3) Squalidus gracilis majimae Hemiculter eigenmanni 9 6 7.5.9 (5) 8. () 5.6 6.6 (9) 7.5 (8) Total b 83 39.9 9.6 ().7 8 (,5) 33. 3 (9) 9..5 (8) a No. of metacercariae detected (Av: average). b Total 83 freshwater fishes in 5 species were examined.
Sohn et al.: Trematode metacercariae in fish from Hantangang and Imjingang 93 was mixed with artificial gastric juice, and the mixture was incubated at 36 C for hr. The digested material was filtered with mm of mesh, and washed with.85% saline until the supernatant became clear. The sediment was carefully examined using a stereomicroscope. Each species of digenetic trematode metacercariae were separately collected by the general morphologic features [,], and they were counted to get the infection rates and densities by fish species. RESULTS Metagonimus spp. metacercariae The metacercariae of Metagonimus spp. were detected in 3 (6.%) out of 5 fishes (in 9 spp.) from the water systems of Hantangang, and their average number was 7.5 per fish infected. Their infection status by the fish species and fish collection sites are revealed in Table. Metagonimus spp. metacercariae were found in total 3 (59.%) out of 9 fishes (in 8 spp.) from the water systems of Imjingang, and their average number was 9.6 per fish infected. Their infection status by the fish species and surveyed areas are shown in Table. Centrocestus armatus metacercariae The metacercariae of C. armatus were detected in 6 (75.%) out of 79 fishes (in spp.) from the water systems of Hantangang, and their average number was 69 per fish infected. Among the positive fish species, especially species of chubs, and Zacco temminckii from Hantangang in Cheorwongun and Z. platypus from Chatancheon in Yeoncheongun were heavily infected with C. armatus metacercariae. Their infection status by the fish species and fish collection sites are shown in Table. C. armatus metacercariae were found in 7 (79.6%) out of 88 fishes (in spp.) from the water systems of Imjingang, and their average number was 8 per fish infected. The infection status of each fish species with C. armatus metacercariae and surveyed areas are presented in Table. 6 fish species were infected with the metacercariae, and their average number was 6.6 per fish infected. The infection status by fish species and surveyed areas are depicted in Tables and. To obtain the adult fluke, the echinostome metacercariae collected in 3 fish species (Odontobutis platycephala, Pseudogobio esocinus, and ) from Munsancheon were orally infected to albino rats. Adult flukes of Echinostoma hortense were recovered only in the small intestines of rats infected with the metacercariae from O. platycephala. The echinostome metacercariae from P. esocinus and H. longirostris were morphologically identical with those of E. hortense from O. platycephala, but seemed less viable. The metacercariae of E. hortense were elliptical and 575 (56) 95 (8) μm in size, had suckers, a head crown with 7 collar spines including corner spines in each end, rows of excretory granules (Fig. ). Diplostomum spp. mesocercariae Diplostomum spp. mesocercariae ( = diplostomula) were detected in fishes from all surveyed areas in water systems of Hantangang and Imjingang. Their infection status by the fish species and surveyed areas are shown in Tables and. Echinostoma spp. metacercariae Echinostoma spp. metacercariae were detected in 5 (.%) out of 97 fishes (in spp.) from the water systems of Hantangang, and their average number was 9.6 per fish infected. They were also found in 9 (6.8%) out of 5 fishes (in 9 spp.) from 3 surveyed sites of Imjingang, and their average density was 3. per fish infected. Especially in Munsancheon, Fig.. A metacercaria of Echinostoma hortense found in Odontobutis platycephala in Munsancheon, Pajusi, Gyeonggido, which is elliptical and 56 8 μm in average size, has suckers, a head crown with 7 collar spines including corner ones (encircled) in each end, and rows of excretory granules (EG).
9 Korean J Parasitol Vol. 53, No. 3: 8998, June 5 Table 3. Infection status of Clonorchis sinensis metacercariae in fishes from Hantangang and Munsancheon in Korea Locality and fish species examined No. of fish examined No. (%)of fish infected No. of metacercariae detected Total Range Average Hantangang (Cheorwongun, Gangwondo) Microphysogobio longidorsalis Hemibarbus mylodon Munsancheon (Pajusi, Gyeonggido) Pseudorasbora parva Carassius auratus Abbotina revulais Hemiculter eigenmanni Squalidus gracilis majimae 35 9 95 3 3 6 5 (.) (.9) (5.3) 7 (7.) (85.3) (6.7) (5.) (83.3) (6.7) () () (.) 3,69 7 8 6,3 3 3, 6, Total 95 7 (.),36, 3.6.9 5.9 8.5 8. 6 35.6 Fig.. A metacercaria of Clonorchis sinensis collected from Pseudorasbora parva in Munsancheon, Pajusi, Gyeonggido, which is elliptical and 58 38 μm in average size, has nearlyequal sized suckers (OS: oral & VS: ventral sucker), brownish pigment granules and an Oshaped excretory bladder (EB). Fig. 3. A metacercaria of Stephanoprora sp. detected in Z. platypus from Seokjangcheon in Yeoncheongun, Gyeonggido, which is elliptical, 8 98 μm in average size, has color spines interrupted in the dorsomedian of oral sucker, minute excretory granules and yellowish pigment. Scale bar is 5 μm. Clonorchis sinensis metacercariae The metacercariae of C. sinensis were detected in 7 (7.%) out of 95 fishes in 3 species (, Microphysogobio longidorsalis, and Hemibarbus mylodon), from Hantangang in Cheorwongun, Gangwondo, and their average density was.9 per fish infected. They were also found in (.%) fishes in 7 species from Munsancheon, and their average density was 35.6 per fish infected. The infection status by the fish species and the locality are designated in Table 3. The metacercariae of C. sinensis collected from Pseudorasbora parva in Munsancheon were elliptical and 37 (58) 355 (38) μm in size, had nearly equalsized suckers, brownish pigment granules, and an Oshaped excretory bladder (Fig. ).
Sohn et al.: Trematode metacercariae in fish from Hantangang and Imjingang 95 Table. Infection status of Stephanoprora spp. metacercariae in fishes from the water systems of Hantangang and Imjingang in Korea Locality and fish species examined No. of fish examined No. (%) of fish infected No. of metacercariae detected Total Range Average Chatancheon (Yeoncheongun, Gyeonggido) (.) Imjingang (Yeoncheongun, Gyeonggido) Acheilognathus yamatsutae 3 (5.) (5.) (.) Seokjangcheon (Yeoncheongun, Gyeonggido) 8 6 (33.3) 33 5.5 Total 83 (3.3) 3.8 7 8 3 3.3 Stephanoprora spp. metacercariae Stephanoprora spp. metacercariae were detected in fish species, i.e., Z. platypus and Acheilognathus yamatsutae, from 3 surveyed areas. Their infection status by the fish species and surveyed areas are shown in Table. They were elliptical in shape, 338 (8) 9 (98) μm in size, had color spines interrupted in dorsomedially, minute excretory granules, and yellowish pigment (Fig. 3). Other trematode metacercariae Clinostomum complanatum metacercariae were found in fish species, P. herzi (in only of fish examined) and H. longirostris (in of 7 fish: 8.6%), from Chatancheon, and their number was. per fish infected respectively. Metorchis orientalis metacercariae were detected in 3 fish species, P. parva (in of 3 fish examined: 3.3%), P. esocinus (in of 3 fish) and Abbotina rivularis (in 8 of fish: 66.7%), from Munsancheon, and their numbers per fish infected were 3.5,., and.5 respectively. Metorchis taiwanensis metacercariae were found in fish species, P. parva (in 3 of 3 fish examined) and O. platycephala (in of 3 fish: 6.7%), from Munsancheon, and their average numbers were. and.5 per fish infected, respectively. DISCUSSION Kim et al. [] reported that all fishes from upper regions of Cheongjusi, Chungcheongbukdo were negative for C. sinensis metacercariae. However, Cho et al. [5] detected C. sinensis metacercariae in fish species, and Squalidus japonicus coreanus, only from Hantangang in Cheorwongun, among 9 localities surveyed in Gangwondo. Cho et al. [] also found them in fish species, i.e., P. herzi, S. japonicus coreanus, Acheilognathus rhombeus, and Ladislabia taczanowskii, from Hantangang in Cheorwongun. In the present study, we also detected C. sinensis metacercariae in 3 fish species, i.e., P. herzi, Microphysogobio longidorsalis, and Hemibarbus mylodon, from Hantangang in Cheorwongun, Gangwondo, although their densities were very low. Therefore, it is confirmed again that the life cycle of C. sinensis is still maintained in some limited areas of Hantangang in Cheorwongun, Gangwondo. In addition, we also found C. sinensis metacercariae in 7 fish species from Munsancheon in Pajusi, Gyeonggido. This finding is the first on the presence of C. sinensis metacercariae in fish from the water systems of Imjingang. Therefore, it is interesting and important in epidemiological aspects of clonorchiasis. Further intensive studies on the snail and other fish intermediate hosts, humans, and reservoir definitive hosts should be investigated in the near future in the water systems of Imjingang. A successful fish collection is a prerequisite in epidemiological surveys of FZT metacercarial infections like the present study. However, we failed to do it in some surveyed areas such as Hantangang in Yeoncheongun, Yeongpyeongcheon, and Seokjangcheon. In these 3 areas, the water current was so rapid and turbulent, the fish collection was possible only by the casting net at the daytime. Whereas in case of Hantangang in Cheorwongun, and Munsancheon, fish catching methods, i.e., netting and casting net, were used together to collect various species of fish. Especially, the netting was a recommendable method for the collection of nocturnal fish species. In the Republic of Korea, Chun [3] described more than species of DTM, i.e., C. sinensis, Metorchis orientalis, Exorchis oviformis, Pseudexorchis major, Echinochasmus japonicus, E. perfoliatus, Cyathocotyle orientalis, C. armatus, Metacercaria hasegawai, Rhypidocotyle lingualis, Diplostomum sp., and unidentified spe
96 Korean J Parasitol Vol. 53, No. 3: 8998, June 5 cies, in 6 fish species from streams and ponds in adjacent areas of Nakdonggang. Lee [] reported more than species of DTM found in fish species from Geumhogang, a branch of Nakdonggang, in Daegu Metropolitan City. Rhee et al. [6,7] detected more than 3 species of DTM, i.e., C. sinensis, M. orientalis, M. taiwanensis, Metagonimus spp., E. oviformis, P. major, E. japonicus, E. hortense, C. orientalis, Holostephanus nipponicus, C. armatus, Metacercaria hasegawai, and Diplostomum orientale, in 3 and 33 fish species from Mangyeonggang and Dongjingang in Jeollabukdo. Besides, several studies were performed on the infection status of DTM in freshwater fishes along the riverside areas of Gyeongsangdo [5,8]. In the present study, we investigated the infection status of 9 DTM, i.e., C. sinensis, Metagonimus spp., C. armatus, Echinostoma spp., Diplostomum sp., Stephanoprora sp., M. orientalis, M. taiwanensis, and C. complanatum, and did not detect 5 species, i.e., Metacercaria hasegawai, E. oviformis, P. major, C. orientalis, and H. nipponicum, among the list of DTM described previously. The present study is meaningful as the first trial on the investigation of DTM infections in fishes from the northern regions of the Korean peninsula, although some studies on FZT metacercariae infections were conducted in fishes from Hantangang in Cheorwongun, Gangwondo [5,]. Stephanoprora sp. is newly added among the list of DTM in Korea. This genus, Stephanoprora, is a group of the Family Echinostomatidae, and mainly found from birds and rarely from mammals. Chai et al. [3] already described Stephanoprora sp. adult recovered in the small intestine of a stray cat from a local market of Busan Metropolitan City. They tentatively called it Stephanoprora sp., but they mentioned that it should be considered identical with S. denticulata although there are minor differences in some morphological features. We were unable to obtain the adult worms from an experimental infection of animals with Stephanoprora sp. metacercariae. However, in faunistic points of view, we should continuously pay attention to this interesting collarspined echinostome in Korea. Among 9 species of DTM subjected in this study, Metagonimus spp. were the most highly prevalent, detected in (8.5%) out of 877 fishes examined, and their prevalence was 6.5% among the positive fish species group, total 7 fish. However, their metacercarial burdens were relatively low. The burden of Metagonimus spp. was the highest in fishes from Hantangang in Cheorwongun, more than 8 (average), and it was less than in fishes from remaining 7 localities. Unlike Cho et al. [], the susceptible fish species, i.e., Plecoglossus altivelis and Tribolodon hakonensis, were not examined in this study. On the other hand, at least 6 fish species (in genera) were reported as the second intermediate host of Metagonimus spp. in Korea [,]. In the present study, Metagonimus spp. metacercariae were found in fish species from the water systems of Hantangang and Imjingang. All fish species except for Acheilognathus koreensis were already listed among the fish intermediate hosts of Metagonimus spp. previously in Korea [,]. A total of fish species in genera were previously listed as the second intermediate hosts of C. armatus in Korea [,,]. In this study, the metacercariae of C. armatus were detected in 5 fish species, Z. platypus, Z. temminckii, A. rhombeus, A. yamatsutae, and A. macropterus from the water systems of Hantangang and Imjingang. Especially, species of chubs, Z. platypus and Z. temminckii from Hantangang in Cheorwongun were highly and heavily infected. These findings agreed well with Cho et al. []. The high prevalence and heavy metacercarial burden in species of chubs were found in almost all regions of Ganwondo surveyed. In addition, species of bitterlings, i.e., A. yamatsutae and A. macropterus, were first confirmed as the fish hosts of C. armatus in this study. Accordingly, total 6 fish species in genera are included among the second intermediate hosts of C. armatus in Korea. In the present study, Echinostoma spp. metacercariae were detected in 5 fish species, but their species names could not be determined. Although 3 species, i.e., Echinostoma cinetorchis, E. hortense, and Echinostoma revolutum, have been known to exist in Korea, there are possibilities for distribution of other Echinostoma spp. infecting birds and mammals via fish intermediate hosts. Among the 3 echinostome species, E. hortense is the dominant zoonotic species, and 8 fish species, i.e., Misgurnus anguillicaudatus, Misgurnus mizolepis, R. oxycephalus, Odontobutis interrupta, S. japonicus coreanus, Rhinogobius brunneus, A. macropterus, and Acanthogobius flavimanus, have been reported as the second intermediate hosts in Korea [,9,]. On the other hand, some fish species, i.e., O. platycephala, P. esocinus, and H. longirostris, from Munsancheon were highly infected with Echinostoma spp. metacercariae. In the adult worm recovery experiment, E. hortense adult flukes were harvested in the small intestines of experimentally infected rats. Diplostomula are the metacercariae (mesocercariae) of Diplostoma spp. (Digenea: Diplostomidae) and lodge in fish and amphibians. Adult worms infect mainly birds and rarely in mammals. In the present study, diplostomula were detected in
Sohn et al.: Trematode metacercariae in fish from Hantangang and Imjingang 97 fishes from all surveyed areas. Total 3 fish species, i.e., A. rivulairs, A. koreensis, C. capio, H. longirostris, H. labeo, H. mylodon, M. longidorsalis, P. esocinus, P. parva, P. herzi, R. ocellatus, Z. platypus, and Z. temminckii, are listed among the second intermediate hosts of unknown Diplostoma spp. in Korea. Among these fish hosts, P. esocinus from Namdaecheon and Munsancheon were most highly and heavily infected. Rhee et al. [7] detected diplostomula in a loach, Misgurnus anguillicaudatus, from Dongjingang in Jeollabukdo, and named them as Diplostoma orientale. However, they did not try to recover the adult flukes, and identified them with mesocercariae only. If it is so, what species of Diplostoma are distributed in Korea? The species determination of Diplostoma mesocercariae infected in fish hosts is one of the taxonomic problems to be solved with recovery of the adult flukes in Korea. Conclusively, it is confirmed for the first time in Korea that a variety of trematode species are inhabited in fishes from the water systems of Hantangang and Imjingang, in northern parts of South Korea. In epidemiological aspects of FZT infections, these regions are endemic areas of intestinal flukes, i.e., Metagonimus spp., C. armatus, and Echinostoma spp., rather than C. sinensis. ACKNOWLEDGMENTS This study was supported by a grant from Korea Association of Health Promotion (3). We thank JungA Kim and Hee Joo Kim, Department of Parasitology and Tropical Medicine, Gyeongsang National University School of Medicine, Jinju, Korea, for their help in examination of fish. CONFLICT OF INTEREST The authors have no conflicts of interest concerning the work reported in this paper. REFERENCES. Sohn WM. Fishborne zoonotic trematode metacercariae in the Republic of Korea. Korean J Parasitol 9; 7 (suppl): S3 S3.. Sohn WM. Invertebrate Founa of Korea Vol. 6, No.. Trematodes. Incheon, Korea. The National Institute of Biological Resources. 3. pp. 3. Chun SK. Studies on some trematodes whose intermediate hosts are fishes in the Naktong river. Bull Fish Coll 96; : 38 (in Korean).. Lee JT. Studies on the metacercariae from freshwater fishes in the KumHo River. Korean J Parasitol 968; 6: 7799. 5. Hwang JT, Choi DW. Changing pattern of infestation with larval trematodes from freshwater fish in river Kumho, Kyungpook Province, Korea. Kyungpook Univ Med J 98; : 675. 6. Rhee JK, Lee HI, Baek BK, Kim PG. Survey on encysted cercariae of trematodes from freshwater fishes in Mangyeong riverside area. Korean J Parasitol 983; : 879. 7. Rhee JK, Rim MH, Baek BK, Lee HI. Survey on encysted cercariae of trematodes from freshwater fishes in Tongjin riverside areas in Korea. Korean J Parasitol 98; : 9. 8. Joo CY. Changing pattern of infection with digenetic larval trematodes from freshwater fish in river Taewha, Kyongnam Province. Korean J Parasitol 988; 6: 637. 9. Kong HH, Choi BR, Moon HC, Choi DW. Larval digenetic trematodes from freshwater fish in river Miryang, Korea. Jpn J Parasitol 995; : 8.. Sohn WM, Choi YS. Infection status with trematode metacercariae in the freshwater fish from Chunamchosuchi (pond), Uichanggun, Kyongsangnamdo, Korea. Korean J Parasitol 997; 35: 657.. Seo BS, Lee SH, Cho SY, Chai JY, Hong ST, Han IS, Sohn JS, Cho BH, Ahn SR, Lee SK, Chung SC, Kang KS, Shim HS, Hwang IS. An epidemiologic study on clonorchiasis and metagonimiasis in riverside areas in Korea. Korean J Parasitol 98; 9: 375.. Cho SH, Lee KY, Lee BC, Cho PY, Cheun HI, Hong ST, Sohn WM, Kim TS. Prevalence of clonorchiasis in southern endemic areas of Korea in 6. Korean J Parasitol 8; 6: 3337. 3. Kim HK, Cheun HI, Chung BS, Lee KY, Kim TS, Lee SE, Lee WJ, Cho SH. Prevalence of Clonorchis sinensis infections along the five major rivers in Republic of Korea, 7. Public Health Res Perspect ; : 39.. Kim EM, Kim JL, Choi SY, Kim JW, Kim S, Choi MH, Bae YM, Lee SH, Hong ST. Infection status of freshwater fish with metacercariae of Clonorchis sinensis in Korea. Korean J Paraitol 8; 6: 7. 5. Cho SH, Sohn WM, Na BK, Kim TS, Kong Y, Eom KS, Seok WS, Lee T. Prevalence of Clonorchis sinensis metacercariae in freshwater fish from three latitudinal regions of the Korean peninsula. Korean J Parasitol ; 9: 385398. 6. Seo BS, Hong ST, Chai JY, Lee SH. Study on Metagonimus yokogawai (Katsurada, 9) in Korea. VI. The geographical distribution of metacercarial infection in sweetfish along the east and south coast. Korean J Parasitol 98; : 83 (in Korean). 7. Song CY, Lee SH, Jeon SR. Studies on the intestinal fluke, Metagonimus yokogawai Katsurada, 9 in Korea. IV. Geographical distribution of sweetfish and infection status with Metagonimus metacercariae in southeastern area of Korea. Korean J Parasitol 985; 3: 338 (in Korean). 8. Cho SH, Kim TS, Na BK, Sohn WM. Prevalence of Metagonimus metacercariae in sweetfish, Plecoglossus altivelis, from eastern and southern coastal areas in Korea. Korean J Parasitol ; 9: 6
98 Korean J Parasitol Vol. 53, No. 3: 8998, June 5 65. 9. Ryang YS, Ahn YK, Lee KW, Kim TS, Hhan MH. Two cases of natural human infection by Echinostoma hortense and its second intermediate host in Wonju area. Korean J Parasitol 985; 3: 33 (in Korean).. Kim DG, Kim TS, Cho SH, Song HJ, Sohn WM. Heterophyid metacercarial infections in brackish water fishes from Jinjuman (Bay), Kyongsangnamdo, Korea. Korean J Parasitol 6; : 73.. Hong SJ, Woo HC, Kim IT. Study on Centrocestus armatus in Korea. I. Infection status of and Z. temminckii with the metacercariae of C. armatus. Korean J Parasitol 989; 7: 6 (in Korean).. Cho SH, Lee WJ, Kim TS, Seok WS, Lee TJ, Jeong KJ, Na BK, Sohn WM. Prevalence of zoonotic trematode metacercariae in freshwater fish from Gangwondo, Korea. Korean J Parasitol ; 5: 399. 3. Chai JY, Bahk YY, Sohn WM. Trematodes recovered in the small intestine of stray cats in the Republic of Korea. Korean J Parasitol 3; 5: 996.