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Original Article

Infection characteristics of Diplostomum species (Digenea: Diplostomidae) metacercariae in fishes from Korea

Woon-Mok Sohn1,*orcid, Byoung-Kuk Na1,2orcid, Jung-A Kim1,2, Hee-Ju Kim1
Parasites, Hosts and Diseases 2026;64(3):195-202.
Published online: July 2, 2026

1Department of Parasitology and Tropical Medicine, Institute of Medical Science, Gyeongsang National University College of Medicine, Jinju, Korea

2Department of Convergence Medical Science, Gyeongsang National University, Jinju, Korea

*Correspondence: wmsohn@gnu.ac.kr

Citation Sohn WM, Na BK, Kim JA, Kim HJ. Infection characteristics of Diplostomum species (Digenea: Diplostomidae) metacercariae in fishes from Korea. Parasites Hosts Dis 2026;64(3):195-202.

• Received: January 15, 2026   • Accepted: May 9, 2026

© 2026, Korean Society for Parasitology and Tropical Medicine

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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  • 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 SHemibarbus longirostrisS, 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.
  • Key words: Diplostomum spp., metacercaria, susceptibility index, endemicity, second intermediate fish host
Digenetic trematodes (subclass Digenea) are a larger taxonomic group, and they have 2 intermediate and 1 definitive hosts in their life cycle. Various species of vertebrates, i.e., fish, amphibian, reptilian and arthropod, act as the second intermediate hosts, which retained the infective larvae, metacercariae. Digenetic trematode metacercariae (DTM) are mainly inhabited in fish intermediate hosts, and they are microscopically distinguished by the morphological characteristics [1-3]. In Korea, since Chun [4] reported various DTM in 16 fish species collected from streams and ponds in adjacent areas of Nakdong-gang (gang means river), many Korean workers have been investigated the infection status with DTM in fishes from various local areas [5-14]. Especially, they have frequently surveyed the infection status of fishborne zoonotic trematodes, i.e., Clonorchis sinensis, Metagonimus spp. including M. yokogawai, Centrocestus armatus, Isthmiophora hortensis and Clinostomum complanatum, metacercariae in Korea [15-32]. Meanwhile, the metacercarial surveys on the infection status of non-human infecting species including Diplostomum spp. have not been widely conducted in fish hosts of Korea [4-14].
In the genus Diplostomum von Nordmann 1832, more than 40 nominal species have been described in the world [1,33]. However, the debate on the species validity existed long time because of taxonomic problems. Recently, several species including D. spathaceum (Rudolphi, 1819), D. pseudospathaceum Niewiadomska, 1984, D. ardeae Dubois, 1969 and D. baeri Dubois, 1937 were identified with the morphological and molecular studies [33,34]. In Korea, D. spathaceum adults recovered in the intestines of a herring gull, Larus argentatus, were only reported by Lee et al. [35]. The metacercariae of Diplostomum spp. (DsMc) were first described from catfish, Parasilurus asotus (= Silurus asotus) by Chun [4]. After that, several Korean workers reported the infection status of DsMc together with other DTM in fishes from specific limited regions of Korea [6,8,9-14]. On the other hand, our team had conducted the surveys on the metacercarial infections of C. sinensis in fishes from 9 wide water systems, i.e., Hantan-gang and Imjin-gang, Han-gang, Geum-gang, Mangyeong-gang, Yeongsan-gang, Tamjin-gang, Seomjin-gang, Nakdong-gang and streams in east coast, of Korea for a long time [11,14-24]. Among the data of these surveys, only the infection data of DsMc were gathered and arranged to report them here after excluding the our previous studies with DsMc data [11,13,14].
Ethics statement
Not applicable.
Fish collection and examination for DsMc
A total of 15,879 fishes in 79 species were collected and examined from 9 major water systems, i.e., Hantan-gang and Imjin-gang, Han-gang, Geum-gang, Mangyeong-gang, Yeongsan-gang, Tamjin-gang, Seomjin-gang, Nakdong-gang and streams in east coast, of Korea. The information on the fishes examined by the survey localities was detailedly shown in Supplementary Tables S1-S13, respectively. The survey localities on the map were nearly included in the map of Sohn [29].
All collected fishes with ice were transported to the laboratory of the Department of Parasitology and Tropical Medicine, Gyeongsang National University College of Medicine, Jinju, Korea. The fish species was identified, after which individual fish was finely ground in a mortar with pestle. The ground fish meat was mixed with artificial gastric juice, and incubated at 36C for about 2 h. The digested material was filtered through a mesh (pore size 1×1 mm) and washed with 0.85% saline until the supernatant became clear. The sediment was carefully examined under a stereomicroscope. DsMc were separately collected according to a previously described method [3]. The morphologies of 45 DsMc from Pseudogobio esocinus, Squalidus chankensis and Zacco platypus were observed under a light microscope (Olympus BH-22, Olympus) with a micrometer after the previously described procedures for specimen [2,3]. The measurement unit for the morphologies of DsMc was designated with μm. DsMc detected from each fish were counted to determine the infection rate (No. of fish with DsMc/No. of fish examined × 100) and intensity (No. of DsMc detected/No. of fish infected) by fish species and survey localities. The susceptibility index (SI) of DsMc in index fish, Zacco platypus was calculated by the formula, prevalence/100 × mean metacercarial intensity per fish infected (PFI).
Morphology of Diplostomum spp. metacercariae (n=45)
Body elongate-oval, dorso-ventrally flat, 327–480 (376) × 225–297 (263) with a primordial hindbody. Oral sucker oval, 38–50 (45) × 35–50 (43). Two contractile lappets (pseudosuckers) present on each side of oral sucker. Prepharynx very short; pharynx elongate-oval, 15–50 (36) × 13–32 (18); oesophagus short; ceca long, wide, reach posterior to tribocytic (holdfast) organ. Ventral sucker transversely oval, 28–50 (41) × 45–63 (54). Tribocytic organ large, transversely oval, 53–85 (62) × 43–106 (80). Reserve excretory system with numerous, relatively large excretory granules, distributed in a median and 2 lateral fields (Fig. 1).
Overall infection status with DsMc by positive fish species
DsMc were detected in 3,831 (24.1%) out of 15,879 fishes in 79 fish species examined. The overall infection status of DsMc by the fish species was detailedly revealed in Table 1. No DsMc were detected from 386 fishes in 31 spp., i.e. Gnathopogon strigatus (n=45), Mugil cephalus (39), Microphysogobio yaluensis (34), Ladislabia taczanowskii (34), Cobitis sinensis (22), Misgurnus anguillicaudatus (21), Iksookimia koreensis (20), Liobagrus mediadiposalis (20), Erythroculter erythropterus (20), Liobagrus andersoni (18), Chaenogobius castaneus (17), Pseudobagrus fulvidraco (16), Cottus hangiongensis (13), Rhodeus pseudosericeus (10), Iksookimia longicorpa (9), Liobagrus somjinensis (9), Culter brevicauda (5), S. asotus (5), Cobitis lutheri (5), Acanthogobius flavimanus (4), Koreocobitis naktongensis (4), Hypomesus nipponensis (3), Cobitis tetralineata (2), Squalidus multimaculatus (2), Koreocobitis rotundicaudata (2), Hemiculter leucisculus (2), Microphysogobio jeoni (1), Acheilognathus signifer (1), Orthrias nudus (1), Misgurnus mizolepis (1), and Phoxinus phoxinus (1). The infection status by the fish species and survey localities was detailedly shown in Supplementary Tables S1-S13, respectively.
Infection status with DsMc by survey localities
DsMc were detected in 3,831 (24.1%) out of 15,879 fishes examined and their infection intensity was 7.2 PFI in average. The prevalence was highest in fishes from Yeongsan-gang (59.3%) and followed by the middle reaches of Seomjin-gang in Gokseong-gun (gun means county) and Gurye-gun, Jeollanam-do (do means province) (48.0%) and Geum-gang (32.3%). That of remain 10 localities was 1.1%–31.3% respectively. The intensity of infection was also highest, 83.1 PFI, in fish from Yeongsan-gang. That of streams in east coast was 11.3 PFI and those of remain 11 localities were 2.1–7.5 PFI respectively. The infection status with DsMc by the survey localities was revealed in Table 2 in detail.
Infection status with DsMc in index fish, Z. platypus, by survey localities
DsMc were detected in 1,038 (44.8%) out of 2,319 Z. platypus examined and their infection intensity was 7.5 PFI in average. The higher prevalence was revealed in the middle reaches of Seomjin-gang (79.6%), Geum-gang (79.2%), and Tamjin-gang (64.7%). SI in index fish was highest (13.64) in 69 (48.9%) out of 141 Z. platypus from streams in east coast, followed by the middle reaches of Seomjin-gang in Gokseong-gun and Gurye-gun, Jeollanam-do (7.56) and Mangyeong-gang (4.75). That of remain 10 localities was 0–3.88 respectively. The infection status with DsMc in index fish, Z. platypus, was detailedly shown in Table 3.
We described the morphologies of DsMc collected from 3 fish species, i.e., P. esocinus, S. chankensis and Z. platypus, which were susceptible hosts to obtain DsMc specimens easily, in this study. Among 14 genus in Diplostominae, 2 ones, genus Diplostomum and Tylodelphys, have the possibility to be present in Korean peninsula by the closely related biological factors, the geographical distribution and second intermediate hosts (fish) [1]. The metacercariae of Diplostomum spp. have been well known, already reported by many Korean workers and they have been detected only in fishes [4,6,8,11-14]. However, those of Tylodelphys spp. have not been reported yet in Korea and they have been found in fishes and amphibians. The metacercarial morphologies of Tylodelphys spp. are obviously differentiated from Diplostomum spp. metacercariae by the more slender body, no lappets on each side of oral sucker and a long elliptical tribocytic organ [1]. Interspecies differentiation of Diplostomum spp. metacercariae is not easy only with morphological characters. Several species of Diplostomum metacercariae, i.e., D. spathaceum, D. pseudospathaceum, D. ardeae, D. baeri, and D. phoxini, were identified with the morphological and molecular studies [33,34]. Therefore, the morphological and molecular studies on the species-validity of DsMc detected by the fish species and survey localities should be performed in the future in Korea.
The DsMc were detected from 48 (60.8%) out of 79 fish species examined in this study. Among 48 positive fish species (PFS), 18 ones, Abbotina revularis, Acanthorhodeus gracilis, A. macropterus, Acheilognathus koreensis, Carassius auratus, Cyprinus capio, Hemibarbus labeo, H. longirostris, Hemiculter eigenmanni, Lepomis macrochirus, Microphysogobio longidorsalis, P. esocinus, Pseudorasbora parva, Pungtungia herzi, Rhodeus ocellatus, Tribolodon hakonensis, Z. platypus, and Z. temminckii (= Nipponocypris temminckii), were already reported as the 2nd intermediate hosts of Diplostomum spp. in Korea [4-14]. The remaining 30 fish species are regarded as new second intermediate hosts of Diplostomum spp. in Korea. In previous studies, a total of 4 fish species (DsMc negative in this study: S. asotus, M. anguillicaudatus, and E. erythropterus, and not examined in this study: Hemibarbus mylodon) were revealed as additional second intermediate hosts of Diplostomum spp. [4,6,8-11,14]. Accordingly, a total of 52 fish species is listed as the second intermediate hosts of Diplostomum spp. by the present and previous studies in Korea.
In this study, the number of fish examined was 2–2,310 (322.8 in average) in 48 fish species of DsMc positive group, but that was 1–45 (12.5 in average) in 31 fish species of DsMc negative group. The number of fish examined was quite different between 2 groups. Fish species in DsMc negative group were not collected a lot in this study. The reason why they might be less prevalent in the water systems surveyed. The fish catching methods, mainly by netting and casting net, and the fish ecology, especially the high prevalence of predatory fish species, i.e., snake head (Channa argus), Mandarin fish (Siniperca scherzeri), Korean aucha perch (Coreaperca herzi), large mouth bass (M. salmoides) and blue gill (L. macrochirus), might be partly affected the small number of fish examined and of even DsMc negative group in some localities. If the fish species in negative group were examined enough, some of them could be convert to the DsMc positive species.
The overall prevalence of DsMc was 24.1% and the infection intensity was 7.2 PFI in average in 48 PFS in this study. Among 48 PFS, the prevalence was highest in P. esocinus (61.5%) and followed by that in S. chankaensis (56.9%), Z. platypus (44.8%), Nipponocypris koreanus (42.8%), N. temminckii (38.5%), H. labeo (38.0%), Acheilognathus lanceolatus (35.8%), and Squalidus japonicus coreanus (32.7%). The mean infection intensity was highest in R. ocellatus (312.0), followed by in H. longirostris (22.1), A. rivularis (15.5), P. esocinus (9.4) and A. gracilis (8.9). In case of R. ocellatus, DsMc were detected in 4 (7.0%) out of 57 fish examined and 1,245 DsMc were extraordinally detected from only 1 fish, which will be the cause of the highest infection intensity. The most susceptible fish with DsMc was P. esocinus (61.5% prevalence and 9.4 infection intensity) in this study. It was previously confirmed by Sohn et al. [11]. They reported 53.8% and 66.7% DsMc prevalence and 8.1 and 28.0 infection intensity in P. esocinus from Hantan-gang and Imjin-gang respectively. On the other hand, Sohn and Choi [8] reported 85.0% and 73.0% DsMc prevalence and 9.5 and 12.0 infection intensity in 2 species of cultrinid fish, E. erythropterus and H. eigenmanni, from Junam-jeosuji (jeosuji means reservoir) in Uichang-gun, Gyeongsangnam-do, Korea. Interestingly, DsMc were found in pond smelt, Hypomesus olidus (= H. nipponensis) [9,10] and sea rundace, T. hakonensis, from 3 coastal lakes in Gangwon-do [13]. From the present and previous studies, we can know that the prevalence and infection intensity of DsMc are somewhat affected by the fish species, the susceptible fish species aforementioned.
The prevalence with DsMc was more or less higher in fishes from Yeongsan-gang (59.3%) and middle reaches of Seomjin-gang (48.0% in Gokseong-gun and Gurye-gun in Jeollanam-do). The intensity of infection with DsMc was much higher in fishes from Yeongsan-gang (83.1 FPI) than in fishes from middle reaches of Seomjin-gang (7.5 FPI). Meanwhile in fishes from streams in east coast, the prevalence (21.3%) was similar with the overall prevalence, but the infection intensity (11.3 PFI) was relatively high. On the other hand, Sohn et al. [11] reported 17.6% DsMc prevalence and 6.9 infection intensity in fishes from Hantan-gang and Imjin-gang. In this study, the prevalence was 20.8%, and the mean infection intensity was 5.2 PFI in fishes from Hantan-gang and Imjin-gang. Sohn and Choi [8] reported 42.3% DsMc prevalence and 10.5 mean infection intensity in 130 fish of 5 species, i.e., E. erythropterus, H. eigenmanni, C. auratus, P. parva and A. macropterus, from Junam-jeosuji. In the same survey locality, Junam-jeosuji, Sohn and Na [14] detected a total of 46 DsMc (2.7 in average) in 17 (7.7%) out of 220 fish in 7 species examined. They also reported 33.9% DsMc prevalence and 2.4 mean infection intensity in 127 fish of 7 species, i.e., E. erythropterus, H. eigenmanni, P. parva, C. auratus, C. carpio, L. macrochirus, and Micropterus salmoides, from Woopo-neup (neup means swamp) in Changnyeong-gun, Gyeongsangnam-do [14]. Choe et al. [12] reported 5.7% DsMc prevalence and 7.3 mean infection intensity in 314 fish of 7 species, Z. platypus, C. auratus, H. longirostris, P. esocinus, P. herzi, L. macrochirus and M. salmoides, from Daecheong-ho (ho means lake) in Chungcheongnam-do. The prevalence and infection intensity of DsMc were much different by the survey localities in this study. However, those of all survey localities (Table 2) except for Nakdong-gang (middle reaches: Wi-cheon) were higher than those of previous studies.
The pale chub, Z. platypus, is widely distributed in the water systems of Korea. They were most dominantly collected in this study. The objective endemicity of DsMc infection was calculated from the index fish, Z. platypus, which was also recommended as the index fish for the infections of Metagonimus spp. metacercariae in Sohn [29]. A total of 2,319 pale chubs were examined, and they were 14.5% of total 15,985 in 48 PFS. The overall DsMc prevalence was 44.8%, the infection intensity was 7.5 PFI and the SI was 3.36 in average. The DsMc prevalence was relatively high in Z. platypus from Seomjin-gang (middle reaches in Jeollanam-do: 79.6%), Geum-gang (79.2%) and Tamjin-gang (64.7%). The infection intensity was somewhat higher in index fish from streams in east coast (27.9), Mangyeong-gang (10.8) and Seomjin-gang (middle reaches: 9.5). The SI was also higher in pale chubs from streams in east coast (13.64), Seomjin-gang (middle reaches: 7.56), and Mangyeong-gang (4.75). The endemicity of DsMc in the index fish (Table 3) was not coincided with that in all fish species examined (Table 2) except for that of Seomjin-gang (middle reaches). In case of all fish species examined, the number of DsMc negative fish is too much included and is affected the prevalence. On the other hand, Sohn et al. [11] reported 27.3% prevalence, 2.2 infection intensity and 0.60 SI in Z. platypus from Hantan-gang and Imjin-gang. In this study, the slightly higher endemicity (1.58 SI) was revealed in index fish from the same locality, Hantan-gang and Imjin-gang. Choe et al. [12] reported 26.0% prevalence, 10.0 infection intensity and 2.60 SI in Z. platypus from Daecheong-ho, Chungcheongnam-do, Korea. From the findings of present and previous studies, we can suppose that the endemicity with DsMc is much higher in index fish, Z. platypus, from streams of east coast and Seomjin-gang (middle reaches) in Jeollanam-do, Korea.
Conclusively, it was confirmed that DsMc are prevalent in various species of fishes in Korea although their prevalence and infection intensity are somewhat different by fish species and survey localities. And then the second intermediate hosts of Diplostomum spp. are obviously listed and consolidated by this study in Korea. The endemicity (SI) of DsMc in index fish, Z. platypus, is regarded as a useful comparative datum in the conjecture of epidemiological situation. Further studies are needed with regard to the species-diversity of Diplostomum spp. flukes in Korea. The species-validity for DsMc detected by the fish species and survey localities should be clarified by molecular genomic studies. Morphological characteristics on the adults recovered from the avian hosts, which are naturally and/or experimentally infected with DsMc, should be precisely described for the fauna of this fluke group in Korea.

Author contributions

Conceptualization: Sohn WM. Data curation: Sohn WM, Na BK, Kim JA. Formal analysis: Sohn WM, Na BK. Investigation: Sohn WM, Na BK, Kim JA, Kim HJ. Methodology: Sohn WM, Na BK, Kim JA. Project administration: Sohn WM, Kim JA. Supervision: Sohn WM. Validation: Sohn WM, Na BK. Visualization: Sohn WM. Writing - original draft: Sohn WM. Writing - review & editing: Sohn WM, Na BK.

Conflict of interest

Woon-Mok Sohn and Byoung-Kuk Na serve as editors of Parasites, Hosts and Diseases but had no involvement in the decision to publish this article. No other potential conflicts of interest relevant to this study were reported.

Supplementary material is available with this article at https://doi.org/10.3347/PHD.26007.
PHD-26007-Supplementary-Table-S1.pdf
PHD-26007-Supplementary-Table-S2.pdf
PHD-26007-Supplementary-Table-S3.pdf
PHD-26007-Supplementary-Table-S4.pdf
PHD-26007-Supplementary-Table-S5.pdf
PHD-26007-Supplementary-Table-S6.pdf
PHD-26007-Supplementary-Table-S7.pdf
PHD-26007-Supplementary-Table-S8.pdf
PHD-26007-Supplementary-Table-S9.pdf
PHD-26007-Supplementary-Table-S10.pdf
PHD-26007-Supplementary-Table-S11.pdf
PHD-26007-Supplementary-Table-S12.pdf
PHD-26007-Supplementary-Table-S13.pdf
Fig. 1.
Diplostomum sp. metacercariae detected in a pale chub, Zacco platypus, from Deokcheon-gang, a branch stream of Nakdong-gang, in Sancheong-gun, Gyeongsangnam-do, Korea. (A) Fresh unstained and (B) acetocarmin stained. L, lappet; OS, oral sucker; P, pharynx; VS, ventral sucker; TO, tribocytic organ. Scale bar=100 μm.
PHD-26007f1.jpg
Table 1.
Overalla infection status of DsMc by the fish species
Table 1.
Positive fish species No. of fish examined No. (%) of fish infected No. of DsMc detected
Range Average
Zacco platypus 2,319 1,038 (44.8) 1–282 7.5
Pungtungia herzi 2,144 124 (5.8) 1–49 3.8
Nipponocypris temminckii 1,033 398 (38.5) 1–60 4.1
Pseudogobio esocinus 1,032 635 (61.5) 1–56 9.4
Carassius auratus 870 63 (7.2) 1–11 2.1
Nipponocypris koreanusb 848 363 (42.8) 1–31 5.8
Hemibarbus longirostris 620 137 (22.1) 1–452 22.1
Acheilognathus koreensis 551 164 (29.8) 1–94 5.1
Coreoperca herzib 532 21 (3.9) 1–7 1.8
Squalidus japonicus coreanusb 447 146 (32.7) 1–33 6.6
Sarcocheilichthys variegatusb 402 3 (0.7) - 1.0
Odontobutis platycephalab 386 32 (8.3) 1–20 3.5
Plecoglossus altivelisb 348 20 (5.7) 1–4 1.7
Acheilognathus yamatsutaeb 345 77 (22.3) 1–29 4.8
Acheilognathus lanceolatusb 330 118 (35.8) 1–28 3.5
Acheilognathus rhombeusb 316 21 (6.6) 1–16 3.4
Coreoleuciscus splendidusb 256 32 (12.5) 1–7 2.4
Acheilognathus majusculusb 213 38 (17.8) 1–13 2.7
Squalidus gracilis majimaeb 207 57 (27.5) 1–32 3.2
Hemibarbus labeo 205 78 (38.0) 1–14 3.5
Squalidus chankaensisb 188 107 (56.9) 1–47 6.7
Sarcocheilichthys nigripinnisb 169 3 (1.8) - 1.0
Pseudorasbora parva 159 5 (3.1) 1–2 1.4
Micropterus salmoidesb 153 2 (1.3) - 1.0
Coreoperca kawamebarib 130 2 (1.5) - 1.0
Odontobutis obscurusb 125 6 (4.8) 1–4 1.8
Opsariichthys uncirostrisb 122 18 (14.8) 1–4 1.9
Rhynchocypris oxycephalusb 111 12 (10.8) 1–5 3.4
Lepomis macrochirus 105 1 (1.0) - 2.0
Siniperca scherzerib 90 2 (2.2) - 1.0
Acanthorhodeus gracilis 89 7 (7.9) 1–22 8.9
Microphysogobio longidorsalis 82 14 (17.1) 1–12 3.0
Acanthorhodeus macropterus 81 19 (23.5) 1–5 1.7
Microphysogobio koeensisb 75 24 (32.0) 1–11 3.4
Rhodeus ocellatus 57 4 (7.0) 1–1,245 312.0
Hemiculter eigenmanni 52 4 (7.7) 1–3 1.5
Abbottina springerib 47 4 (8.5) 1–2 1.5
Pseudobagrus koreanusb 46 1 (2.2) - 1.0
Tribolodon hakonensis 41 2 (4.9) 1–2 1.5
Abbottina rivularis 38 11 (28.9) 1–70 15.5
Cyprinus capio 38 3 (7.9) 1–4 2.0
Chaenogobius urotaeniab 20 2 (10.0) - 1.0
Tridentiger brevispinisb 19 3 (15.8) 1–5 3.3
Acheilognathus somjinensisb 18 2 (11.1) - 1.0
Onchorhynchus masou masoub 14 3 (21.4) 1–2 1.3
Acanthogobius lactipesb 10 3 (30.0) 1–6 4.3
Channa argusb 8 1 (12.5) - 4.0
Lateolabrax japonicusb 2 1 (50.0) - 5.0
Total 15,879c 3,831 (24.1) 1–1,245 7.2

DsMc, Diplostomum spp. metacercariae.

aA total of 48 fish species was positive with DsMc;

bThirty fish intermediate hosts of Diplostomum spp. newly listed in this study;

cA total of 386 DsMc negative fishes (31 species) was included.

Table 2.
Infection status of DsMc by the survey locality in Korea
Table 2.
Survey locality No.a of fish examined No. (%) of fish infected No. of DsMc detected
Range Average
Hantan-gang and Imjin-gang 1,323 275 (20.8) 1–48 5.2
Han-gang 707 124 (17.5) 1–54 4.2
Geum-gang 830 268 (32.3) 1–28 4.3
Mangyeong-gang 927 223 (24.1) 1–59 6.4
Yeongsan-gang 86 51 (59.3) 1–1,245 83.1
Tamjin-gang 2,201 563 (26.6) 1–52 5.5
Seomjin-gang (upper reaches)b 1,259 347 (27.6) 1–47 6.7
Seomjin-gang (middle reaches)c 1,276 613 (48.0) 1–106 7.5
Seomjin-gang (lower reaches)d 1,161 363 (31.3) 1–40 4.3
Nakdong-gang (upper reaches)e 1,179 269 (22.8) 1–94 6.8
Nakdong-gang (middle reaches)f 1,647 18 (1.1) 1–6 2.1
Nakdong-gang (lower reaches)g 2,057 456 (22.2) 1–65 4.3
Streams in east coast 1,226 261 (21.3) 1–282 11.3
Total 15,879 3,831 (24.1) 1–1,245 7.2

DsMc, Diplostomum spp. metacercariae.

aNo. of fish (No. of fish species) in DsMc negative: 573 (23), 289 (19), 176 (16), 96 (19), 8 (3), 322 (12), 186 (18), 188 (8), 214 (19), 177 (19), 990 (31), 142 (11), and 147 (15) by the survey localities from upper to bottom;

bSeomjin-gang in Jeollabuk-do;

cSeomjin-gang in Jeollanam-do;

dSeomjin-gang in Gyeongsangnam-do;

eNakdong-gang in Gyeongsangbuk-do;

fNakdong-gang (Wi-cheon) in Gyeongsangbuk-do;

gNakdong-gang in Gyeongsangnam-do.

Table 3.
Infection status of DsMc in the index fish, Zacco platypus, by the survey locality in Korea
Table 3.
Survey locality No. of fish examined No. (%) of fish infected No. of DsMc detected
Range Average SIa
Hantan-gang and Imjin-gang 289 134 (46.4) 1–18 3.4 1.58
Han-gang 85 28 (32.9) 1–5 2.1 0.69
Geum-gang 101 80 (79.2) 1–22 4.9 3.88
Mangyeong-gang 100 44 (44.0) 1–59 10.8 4.75
Yeongsan-gang 30 3 (10.0) 1–2 1.3 0.01
Tamjin-gang 266 172 (64.7) 1–49 5.2 3.36
Seomjin-gang (upper reaches)b 182 76 (41.8) 1–34 6.8 2.84
Seomjin-gang (middle reaches)c 206 164 (79.6) 1–106 9.5 7.56
Seomjin-gang (lower reaches)d 185 87 (47.0) 1–21 2.9 1.36
Nakdong-gang (upper reaches)e 211 97 (46.0) 1–64 8.1 3.73
Nakdong-gang (middle reaches)f 326 6 (1.8) 1–3 1.5 0.00
Nakdong-gang (lower reaches)g 197 78 (39.6) 1–65 5.3 2.10
Streams in east coast 141 69 (48.9) 1–282 27.9 13.64
Total 2,319 1,038 (44.8) 1–282 7.5 3.36

DsMc, Diplostomum spp. metacercariae; SI, susceptibility index.

aPrevalence/100 × mean metacercarial intensity per fish infected.

bSeomjin-gang in Jeollabuk-do;

cSeomjin-gang in Jeollanam-do;

dSeomjin-gang in Gyeongsangnam-do;

eNakdong-gang in Gyeongsangbuk-do;

fNakdong-gang (Wi-cheon) in Gyeongsangbuk-do;

gNakdong-gang in Gyeongsangnam-do;

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Infection characteristics of Diplostomum species (Digenea: Diplostomidae) metacercariae in fishes from Korea
Parasites Hosts Dis. 2026;64(3):195-202.   Published online July 2, 2026
DOI: https://doi.org/10.3347/PHD.26007
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Infection characteristics of Diplostomum species (Digenea: Diplostomidae) metacercariae in fishes from Korea
Parasites Hosts Dis. 2026;64(3):195-202.   Published online July 2, 2026
DOI: https://doi.org/10.3347/PHD.26007
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Infection characteristics of Diplostomum species (Digenea: Diplostomidae) metacercariae in fishes from Korea
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Fig. 1. Diplostomum sp. metacercariae detected in a pale chub, Zacco platypus, from Deokcheon-gang, a branch stream of Nakdong-gang, in Sancheong-gun, Gyeongsangnam-do, Korea. (A) Fresh unstained and (B) acetocarmin stained. L, lappet; OS, oral sucker; P, pharynx; VS, ventral sucker; TO, tribocytic organ. Scale bar=100 μm.

Fig. 1.

Infection characteristics of Diplostomum species (Digenea: Diplostomidae) metacercariae in fishes from Korea
Positive fish species No. of fish examined No. (%) of fish infected No. of DsMc detected
Range Average
Zacco platypus 2,319 1,038 (44.8) 1–282 7.5
Pungtungia herzi 2,144 124 (5.8) 1–49 3.8
Nipponocypris temminckii 1,033 398 (38.5) 1–60 4.1
Pseudogobio esocinus 1,032 635 (61.5) 1–56 9.4
Carassius auratus 870 63 (7.2) 1–11 2.1
Nipponocypris koreanusb 848 363 (42.8) 1–31 5.8
Hemibarbus longirostris 620 137 (22.1) 1–452 22.1
Acheilognathus koreensis 551 164 (29.8) 1–94 5.1
Coreoperca herzib 532 21 (3.9) 1–7 1.8
Squalidus japonicus coreanusb 447 146 (32.7) 1–33 6.6
Sarcocheilichthys variegatusb 402 3 (0.7) - 1.0
Odontobutis platycephalab 386 32 (8.3) 1–20 3.5
Plecoglossus altivelisb 348 20 (5.7) 1–4 1.7
Acheilognathus yamatsutaeb 345 77 (22.3) 1–29 4.8
Acheilognathus lanceolatusb 330 118 (35.8) 1–28 3.5
Acheilognathus rhombeusb 316 21 (6.6) 1–16 3.4
Coreoleuciscus splendidusb 256 32 (12.5) 1–7 2.4
Acheilognathus majusculusb 213 38 (17.8) 1–13 2.7
Squalidus gracilis majimaeb 207 57 (27.5) 1–32 3.2
Hemibarbus labeo 205 78 (38.0) 1–14 3.5
Squalidus chankaensisb 188 107 (56.9) 1–47 6.7
Sarcocheilichthys nigripinnisb 169 3 (1.8) - 1.0
Pseudorasbora parva 159 5 (3.1) 1–2 1.4
Micropterus salmoidesb 153 2 (1.3) - 1.0
Coreoperca kawamebarib 130 2 (1.5) - 1.0
Odontobutis obscurusb 125 6 (4.8) 1–4 1.8
Opsariichthys uncirostrisb 122 18 (14.8) 1–4 1.9
Rhynchocypris oxycephalusb 111 12 (10.8) 1–5 3.4
Lepomis macrochirus 105 1 (1.0) - 2.0
Siniperca scherzerib 90 2 (2.2) - 1.0
Acanthorhodeus gracilis 89 7 (7.9) 1–22 8.9
Microphysogobio longidorsalis 82 14 (17.1) 1–12 3.0
Acanthorhodeus macropterus 81 19 (23.5) 1–5 1.7
Microphysogobio koeensisb 75 24 (32.0) 1–11 3.4
Rhodeus ocellatus 57 4 (7.0) 1–1,245 312.0
Hemiculter eigenmanni 52 4 (7.7) 1–3 1.5
Abbottina springerib 47 4 (8.5) 1–2 1.5
Pseudobagrus koreanusb 46 1 (2.2) - 1.0
Tribolodon hakonensis 41 2 (4.9) 1–2 1.5
Abbottina rivularis 38 11 (28.9) 1–70 15.5
Cyprinus capio 38 3 (7.9) 1–4 2.0
Chaenogobius urotaeniab 20 2 (10.0) - 1.0
Tridentiger brevispinisb 19 3 (15.8) 1–5 3.3
Acheilognathus somjinensisb 18 2 (11.1) - 1.0
Onchorhynchus masou masoub 14 3 (21.4) 1–2 1.3
Acanthogobius lactipesb 10 3 (30.0) 1–6 4.3
Channa argusb 8 1 (12.5) - 4.0
Lateolabrax japonicusb 2 1 (50.0) - 5.0
Total 15,879c 3,831 (24.1) 1–1,245 7.2
Survey locality No.a of fish examined No. (%) of fish infected No. of DsMc detected
Range Average
Hantan-gang and Imjin-gang 1,323 275 (20.8) 1–48 5.2
Han-gang 707 124 (17.5) 1–54 4.2
Geum-gang 830 268 (32.3) 1–28 4.3
Mangyeong-gang 927 223 (24.1) 1–59 6.4
Yeongsan-gang 86 51 (59.3) 1–1,245 83.1
Tamjin-gang 2,201 563 (26.6) 1–52 5.5
Seomjin-gang (upper reaches)b 1,259 347 (27.6) 1–47 6.7
Seomjin-gang (middle reaches)c 1,276 613 (48.0) 1–106 7.5
Seomjin-gang (lower reaches)d 1,161 363 (31.3) 1–40 4.3
Nakdong-gang (upper reaches)e 1,179 269 (22.8) 1–94 6.8
Nakdong-gang (middle reaches)f 1,647 18 (1.1) 1–6 2.1
Nakdong-gang (lower reaches)g 2,057 456 (22.2) 1–65 4.3
Streams in east coast 1,226 261 (21.3) 1–282 11.3
Total 15,879 3,831 (24.1) 1–1,245 7.2
Survey locality No. of fish examined No. (%) of fish infected No. of DsMc detected
Range Average SIa
Hantan-gang and Imjin-gang 289 134 (46.4) 1–18 3.4 1.58
Han-gang 85 28 (32.9) 1–5 2.1 0.69
Geum-gang 101 80 (79.2) 1–22 4.9 3.88
Mangyeong-gang 100 44 (44.0) 1–59 10.8 4.75
Yeongsan-gang 30 3 (10.0) 1–2 1.3 0.01
Tamjin-gang 266 172 (64.7) 1–49 5.2 3.36
Seomjin-gang (upper reaches)b 182 76 (41.8) 1–34 6.8 2.84
Seomjin-gang (middle reaches)c 206 164 (79.6) 1–106 9.5 7.56
Seomjin-gang (lower reaches)d 185 87 (47.0) 1–21 2.9 1.36
Nakdong-gang (upper reaches)e 211 97 (46.0) 1–64 8.1 3.73
Nakdong-gang (middle reaches)f 326 6 (1.8) 1–3 1.5 0.00
Nakdong-gang (lower reaches)g 197 78 (39.6) 1–65 5.3 2.10
Streams in east coast 141 69 (48.9) 1–282 27.9 13.64
Total 2,319 1,038 (44.8) 1–282 7.5 3.36
Table 1. Overalla infection status of DsMc by the fish species

DsMc, Diplostomum spp. metacercariae.

A total of 48 fish species was positive with DsMc;

Thirty fish intermediate hosts of Diplostomum spp. newly listed in this study;

A total of 386 DsMc negative fishes (31 species) was included.

Table 2. Infection status of DsMc by the survey locality in Korea

DsMc, Diplostomum spp. metacercariae.

No. of fish (No. of fish species) in DsMc negative: 573 (23), 289 (19), 176 (16), 96 (19), 8 (3), 322 (12), 186 (18), 188 (8), 214 (19), 177 (19), 990 (31), 142 (11), and 147 (15) by the survey localities from upper to bottom;

Seomjin-gang in Jeollabuk-do;

Seomjin-gang in Jeollanam-do;

Seomjin-gang in Gyeongsangnam-do;

Nakdong-gang in Gyeongsangbuk-do;

Nakdong-gang (Wi-cheon) in Gyeongsangbuk-do;

Nakdong-gang in Gyeongsangnam-do.

Table 3. Infection status of DsMc in the index fish, Zacco platypus, by the survey locality in Korea

DsMc, Diplostomum spp. metacercariae; SI, susceptibility index.

Prevalence/100 × mean metacercarial intensity per fish infected.

Seomjin-gang in Jeollabuk-do;

Seomjin-gang in Jeollanam-do;

Seomjin-gang in Gyeongsangnam-do;

Nakdong-gang in Gyeongsangbuk-do;

Nakdong-gang (Wi-cheon) in Gyeongsangbuk-do;

Nakdong-gang in Gyeongsangnam-do;

Table 1.

Table 2.

Table 3.

PHD : Parasites, Hosts and Diseases

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