Discovery of intermediate hosts for two species of blood flukes Cardicola orientalis and Cardicola forsteri (Trematoda: Aporocotylidae) infecting Pacific bluefin tuna in Japan

Abstract

Fish blood flukes (Aporocotylidae) are important pathogens of farmed finfish around the world. Among them, Cardicola spp. infecting farmed tuna are considered to be serious threats to tuna farming and have received tremendous attention. We conducted periodical samplings at a tuna farming site in Japan between January and May, 2015 to determine the life cycle of Cardicola spp. We collected over 4700 terebellid polychaetes from ropes, floats and frames of tuna culture cages and found nearly 400 infected worms. Sporocysts and cercariae found in Nicolea gracilibranchis were genetically identified as Cardicola orientalis by 28S and ITS2 ribosomal DNA sequences. This was the first discovery of the intermediate host for this parasite species. Infection prevalence and the abundance of N. gracilibranchis significantly varied between sampling points and the highest number of infected terebellids were collected from ropes. We also demonstrated morphologically and molecularly that asexual stages found in a single Amphitrite sp. (Terebellidae) and adult worms isolated from farmed juvenile tuna were Cardicola forsteri. This is the first report of C. forsteri in Pacific bluefin tuna (PBT) Thunnus orientalis in Japan. Our results demonstrated that all three species of Cardicola orientalis, C. forsteri and Cardicola opisthorchis exist in Japanese farmed PBTs and that they all use terebellid polychaetes as the intermediate hosts.

First elucidation of a blood fluke (Electrovermis zappum n. gen., n. sp.) life cycle including a chondrichthyan or bivalve

“…The sporocyst of the new species and that of other aporocotylids infecting bivalves is spheroid (Figs. 5 and 6), whereas the sporocyst of aporocotylids infecting polychaetes is elongate with tapered (spindle-shaped) or rounded ends (Cribb et al, 2011; Sugihara et al, 2014; Shirakashi et al, 2016; Siegel et al, 2018). We could not discern a morphological difference between the sporocyst of E. zappum and Holliman's (1961) description of the sporocyst of Cercaria asymmetrica Holliman, 1961.…”

“…Regarding the dorsal fin fold, all bivalve-infecting aporocotylids, which likely all mature in chondrichthyans, have a dorsal fin fold except C. solemyae ; further separating C. solemyae from all other cercariae that infect bivalves, polychaetes, or gastropods. The known blood fluke cercariae from all marine ray-finned fishes (Actinopterygii) lack a dorsal fin fold (Køie, 1982; Cribb et al, 2011; Sugihara et al, 2014; Shirakashi et al, 2016; Siegel et al, 2018; Table 3; KEY). Regarding the penetration glands, C. asymmetrica has seven penetration glands, and Cercaria cristulata Holliman, 1961 has eight (Holliman, 1961); whereas Cercaria mercenaria Wardle, 1979 and C. soleymae have 10 (Martin, 1944; Wardle, 1979).…”

“…Eleven include freshwater hosts: Sanguinicola armata Plehn, 1905 (Sendersky and Dobrovolsky, 2004); S. alseae Meade and Pratt, 1965 (Meade and Pratt, 1965); S. davisi Davis, 1953 (Wales, 1958); S. fontinalis (Hoffman et al, 1985); S. idahoensis (Schell, 1974); S. inermis Plehn, 1905 (Kirk and Lewis, 1993); S. klamathensis Wales, 1958 (Wales, 1958); S. lophophora (Erickson and Wallace, 1959); S. megalobramae (Li, 1980); S. occidentalis (Bacha, 1966); S. rutili (Simón-Martin et al, 1987). Six include marine or estuarine hosts: Aporocotyle simplex Odhner, 1900 (Køie, 1982); Cardicola forsteri Cribb, Daintith, and Munday, 2000 (Cribb et al, 2011); C. laruei Short, 1953 (Siegel et al, 2018); C. opisthorchis Ogawa, Ishimaru, Shirakashi, Takami, and Grabner, 2011 (Sugihara et al, 2014); C. orientalis Ogawa, Tanaka, Sugihara, and Takami, 2010 (Shirakashi et al, 2016); C. parvus Bullard, Baker, and de Buron, 2012 (Siegel et al, 2018). One includes an anadromous definitive host and a freshwater gastropod: Paracardicoloides yamagutii Martin, 1974 (Nolan and Cribb, 2004).…”

“…Müller, 1771 Cardicola fosteri Cribb, Daintith, and Munday, 2000Kushimoto, Wakayama Prefecture, JapanShirakashi et al, 2016 Artacama proboscidea Malmgren, 1866 Aporocotyle simplex Odhner, 1900Øresund, north of the island Veen, DenmarkKøie, 1982 Enoplobranchus sanguineus (Verrill, 1873) Cardicola parvus Bullard and de Buron, 2012Oyster landing, North Inlet; Charleston, South Carolina, USASiegel et al, 2018 Lanassa nordenskioldi Malmgren, 1866 Aporocotyle sp. “morphologically indistinguishable” from Aporocotyle simplex Odhner, 1900Seyðisfjörður, Eastern IcelandKøie and Peterson, 1988 Lanicides vayssierei (Gravier, 1911) Cercaria hartmanae Martin, 1952Cape Boyds, Ross Island, AntarcticaMartin, 1952 Longicarpus modestus (Quatrefages, 1866) Cardicola fosteri Cribb, Daintith, and Munday, 2000off Port Lincoln, South AustraliaCribb et al, 2011 Nicolea gracilibranchis (Grube, 1878) Cardicola orientalis Ogawa, Tanaka, Sugihara, and Takami, 2010Kushimoto, Wakayama Prefecture, JapanShirakashi et al, 2016 Terebella lapidaria Linnaeus, 1767 Cardicola laruei Short, 1953Oyster landing in North Inlet, South Carolina, USASiegel et al, 2018 Terebella sp. Linnaeus, 1767 Cardicola opisthorchis Ogawa, Ishimaru, Shirakashi, Takami, and Grabner, 2011off Tsushima, Nagasaki Prefecture, JapanSugihara et al, 2014…”

Editorial: The biodiversity of trematodes of fishes

“…The potential of molecular approaches for the elucidation of life-cycles has meant that they are fast dominating the field (e.g. Heneberg et al, 2015;Kudlai et al, 2015;Muñoz et al, 2015;Shirakashi et al, 2016). In view of this importance, one paper here outlines 'best practice' for the molecular characterisation of trematodes in detail.…”