Institute of Parasitology, Biology Centre CAS Folia Parasitologica 2020, 67: 028 doi: 10.14411/fp.2020.028 http://folia.paru.cas.cz Research Article Five monogenean species (Allodiscocotylidae, Heteromicrocotylidae, Microcotylidae) from the Pacific seabream Acanthopagrus pacificus (Perciformes: Sparidae) in the Gulf of Tonkin off Vietnam, with descriptions of three new species Ha Van Nguyen1, Hung Manh Nguyen1,6*, Ngo Duy Ha1, Chinh Nguyen Ngoc1, Thanh Bui Ngoc2, Sinh Xuan Le3, Yulia Tatonova4 and Stephen E. Greiman5 1 Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology, Cau Giay, Hanoi, Vietnam; 2 Research Institute for Aquaculture No. 1, Dinh Bang, Tu Son, Bac Ninh province, Vietnam; 3 Institute of Marine Environment and Resources, Ngo Quyen, Hai Phong, Vietnam; 4 Federal Scientific Center of the East Asia Terrestrial Biodiversity, Far Eastern Branch, Russian Academy of Sciences, Vladivostok, Russia; 5 Georgia Southern University, Statesboro, United States of America 6 Graduate University of Science and Technology, Vietnam Academy of Science and Technology, Cau Giay, Hanoi, Vietnam. Abstract: A total of 52 specimens of the Pacific seabream Acanthopagrus pacificus Iwatsuki, Kume et Yoshino from the Gulf of Tonkin off Vietnam were examined for monogeneans. Twenty fish were parasitised by 101 individuals of five monogenean species, including two known species Allodiscocotyla diacanthi Unnithan, 1962 and Heterapta chorinemi (Tripathi, 1956), as well as three new species, Polylabroides tienyenensis sp. n., Polylabroides tonkinensis sp. n. and Metacamopia lebedevi sp. n. Polylabroides tienyenensis and P. tonkinensis are morphologically more similar to Polylabroides guangdongensis Zhang et Yang, 2001 in comparison with other spe- cies within the genus, based on the absence of small spines on the cirrus. However, P. tonkinensis is distinguished from P. guangdon- gensis by fewer clamps on the haptor and by the different shapes of the large spines on the cirrus. Similarly, P. tienyenensis differs from P. guangdongensis by vaginal ducts with fewer branches, fewer clamps and smaller egg size. Metacamopia lebedevi is distinguished from Metacamopia chorinemi (Yamaguti, 1953) by the arrangement of testes (one row vs two rows), diverticula absent in the oesoph- agus, and the number of anchor pairs (one vs two); it differs from Metacamopia oligoplites Takemoto, Amato et Luque, 1996 by the smaller haptor, shape and absence of small sclerotised hooks, the number of ribs in their clamps, and the position of the testes; it can be separated from Metacamopia indica (Unnithan, 1962) by having fewer testes and lacking sclerotised structures in the vagina. The present study also provides the measurements for A. diacanthi, H. chorinemi, and proposes a new key to all species of Polylabroides. Keywords: Polyopisthocotylea taxonomy, Monogenea, marine parasites, sparids, western Pacific The Pacific seabream, Acanthopagrus pacificus Iwatsu- Nagasawa 2015); one species of Pseudaxine Parona et Pe- ki, Kume et Yoshino (Perciformes: Sparidae), is distributed rugia, 1890 (Chauhan 1945); one species of Aspinatrium throughout the western Pacific (Iwatsuki et al. 2010). Hith- Yamaguti, 1963 (Yamaguti 1963); one species of Microcot- erto, there are no records of monogeneans from A. pacifi- yle van Beneden et Hesse, 1863 (Ko and Chan 2002); one cus. However, 37 monogenean species have been recorded species of Udonella Johnston, 1835 (Byrnes 1986a); two from fishes of Acanthopagrus spp., including one species species of Euryhaliotrema Kritsky et Boeger, 2002 (Oga- of Haliotrema Johnston et Tiegs, 1922 (Johnston and Tiegs wa and Egusa 1978a, Kritsky and Boeger 2002, Kritsky 1922, Roubal 1981, Byrnes 1986a); one species of Mur- 2012); two species of Anoplodiscus Sonsino, 1890 (Yama- raytrema Price, 1937 (Zhang and Yang 2001); one species guti 1958, Ogawa and Egusa 1981, Roubal 1981, Byrnes of Encotyllabe Diesing, 1850 (Yamaguti 1934, Nitta and 1986a, Maran et al. 2014); two species of Benedenia Dies- Nagasawa 2015); one species of Lobotrema Tripathi, 1959 ing, 1858 (Byrnes 1986a, Hussey 1986); four species of (Yamaguti 1958, Roubal 1981, Byrnes 1986a, Nitta and Polylabris Euzet et Cauwet, 1967 (Mamaev and Parukhin Address for correspondence: H.M. Nguyen, Department of Parasitology, Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam. Phone: + 84 988688203; Fax: + 84243 8361196; E–mail: [email protected] Zoobank number for article: urn:lsid:zoobank.org:pub:29F9A993-A9EF-4074-8524-B5E3BEF45337 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. doi: 10.14411/fp.2020.028 Nguyen et al.: Five monogeneans from Acanthopagrus pacificus 1976, Ogawa and Egusa 1980, Hussey 1986, Al-Dara- presenting the range followed by the mean and the number of ji et al. 2010); eight species of Polylabroides Mamaev et individuals or structures measured in parentheses. Parukhin, 1976 (Murray 1931, Yamaguti 1963, Mamaev Type specimens and vouchers are deposited at the Department and Parukhin 1976, Roubal 1981, Byrnes 1985, Dillon et of Parasitology, Institute of Ecology and Biological Resources, al. 1985, Mamaev 1988, Zhang and Yang 2001) and one and in the Vietnam National Museum of Nature, Hanoi, Vietnam. species of Lamellodiscus Johnston et Tiegs, 1922 (John- ston and Tiegs 1922, Ogawa and Egusa 1978b, Roubal RESULTS 1981, Byrnes 1986b, Kritsky 2012, Nitta and Nagasawa Twenty individuals of Acanthopagrus pacificus were in- 2015, Zhang et al. 2018). Species of the polyopisthocoty- fected by a total of 101 monogenean specimens. The inten- lean genera Metacamopia Lebedev, 1972, Allodiscocotyla sity of infection varied from 1 to 16 worms per fish. Mor- Yamaguti, 1953, and Heterapta Unnithan, 1961, have nev- phological examination of all 101 monogenean specimens er been reported from fishes of the genus of Acanthopagrus revealed that they represented five species. Among them, Peters. one dominant species consisted of 95 specimens, while the Among the monogenean fauna of marine fishes in Viet- other four species consisted of only one or two specimens nam, Metacamopia and Allodiscocotyla have been found each/species. The details of each species are presented be- infecting different carangid hosts, e.g. Metacamopia indica low. (Unnithan, 1962) in Scomberoides lysan (Forsskål) (Leb- edev 1972, 1986); Metacamopia chorinemi (Yamaguti, Polylabroides tienyenensis sp. n. Figs. 1, 2 1953) in S. lysan and Selar crumenophthalmus (Bloch) (Lebedev 1970, 1986); Allodiscocotyla chorinemi Yama- ZooBank number for species: guti, 1953 in S. lysan, Caranx sp., and Decapterus sp. urn:lsid:zoobank.org:act:38F13E50-5B5E-413A-AD0A-3BA560F57545. (Lebedev 1970); Allodiscocotyla diacanthi Unnithan, 1962 in Decapterus sp. (Lebedev 1970). There are no previous Description (based on one specimen stained in Mayer’s records of species of Heterapta and Polylabroides Ma- carmine and one specimen stained in Gomori’s trichrome) maev et Parukhin, 1976 from the coast of Vietnam. Body elongate, subcylindrical, tapering anteriorly and This study is the first survey of monogeneans from posteriorly, 3.362–3.875 in length, maximum width at level the Pacific seabream, A. pacificus, in the Gulf of Tonkin, of ovary 205–287. Anterior extremity with three slight pro- off Vietnam. Herein, we present the description of one tuberances in which cephalic glands open. Haptor symmet- new species of Metacamopia and two new species of rical, distinctly delineated from body proper, armed with Polylabroides, as well as new host records and measure- 31–36 pairs of clamps (Fig. 1A). Clamps of typical Mi- ment for A. diacanthi and H. chorinemi (Tripathi, 1956). crocotyle-type without accessory sclerite (Figs. 1E, 2C,D), similar in shape, dissimilar in size; the largest clamps in MATERIAL AND METHODS anterior region of haptor, 66–68 × 30–43 (67 × 37) (n = 8); During a survey of the helminth fauna of marine fishes off the middle clamps 64–66 × 31–37 (65 × 34) (n = 8); posterior coast of Vietnam between March 2012 and May 2018, we exam- clamps 41 × 25–31 (41 × 28) (n = 8). ined 52 individuals of Acanthopagrus pacificus collected from Buccal suckers two, muscular, oval, without septa, 53– five locations in the Gulf of Tonkin, e.g. off Mong Cai (21.4463N, 57 × 47–49 (55 × 48) (n = 4). Mouth ventro-subterminal; 107.9438E), Tien Yen (mangrove forest) (21.3052N, 107.4736E), pharynx subglobular, 39–41 in width (Fig. 1B). Oesopha- Quat Lam (20.2016N, 106.3888E), Do Son (20.7211N, gus slender, 230 in length, bifurcating at posterior end of 106.7980E), and Cat Ba (20.7252N, 107.0463E). cirrus, about 272 from anterior extremity. Intestinal caeca Fish were purchased alive from fishermen, placed in an ice two, extending posteriorly but does not enter haptor; right box and carried fresh to the laboratory. All fishes were euthanised and left caeca equal in length. using benzocaine (100 mg/l) within 12 hours before examination. Testes 13, postovarian, globular or elongate-oval, large, Gills were cut out and gill lamellae were placed separately in dissimilar in size, 62–102 × 66–120 (88 × 92) (n = 24); ar- Petri dishes with seawater and checked for the presence of mono- ranged in longitudinal intracaeca row (Fig. 1A). Vas defer- geneans