Crustacean Research 2018 Vol.47: 73–88 ©Carcinological Society of Japan. doi: 10.18353/crustacea.47.0_73 Tachaea chinensis (Isopoda: Corallanidae), an ectoparasite of freshwater shrimps and prawns, from western Japan, with a list of its known collection localities and hosts Kazuya Nagasawa, Tadashi Imai, Hidetoshi Saito Abstract.̶ The corallanid isopod Tachaea chinensis Thielemann, 1910 is a parasite attached on the carapace of freshwater shrimps and prawns. The isopod is reported from Palaemon paucidens De Haan, 1884 (Palaemonidae) at two localities in Kagawa Prefecture (Shikoku) and two localities in Shimane Prefecture (western Honshu), and from Neocaridina sp. (Atyidae) at one locality in Shimane Prefecture, Japan. This represents the first record of T. chinensis from Shikoku. The species is briefly described and illustrated based on non-ovigerous females. Prevalence of T. chinensis in populations of P. paucidens and Neocaridina sp. ranged from 10.7–57.1%, and the intensity of infestation was almost constantly one, which indicates its intra-specific competition on the host carapace. Palaemon paucidens is considered as a preferred host of T. chinensis in Honshu and Shikoku, Japan. Based on the literature published between 1910 and 2018 including this paper, T. chinensis has been reported from 14 nominal and some unidentified species of shrimps and prawns belonging to three atyid genera (Caridina, Neocaridina, and Paratya), two palaemonid genera (Macrobrachium and Palaemon), and one penaeid genus (Penaeus), ranging from temperate (Honshu, Shikoku, and Kyushu in Japan, and central-eastern China) through subtropical (Okinawa in Japan, and Hong Kong in southeastern China) to tropical (Hainan in southeastern China, Vietnam, Thailand, and Malaysia) regions in East Asia. Key words: shrimp parasite, prevalence, geographical distribution, host utilization ■ Introduction and western Japan from 2009 to 2017 (e.g., Imai, 2012; Imai & Oonuki, 2013, 2014, 2017; Tachaea chinensis Thielemann, 1910 is a Imai et al., 2015, 2016, 2017, 2018), we col- parasite found attached on the carapace of lected T. chinensis parasitic on Palaemon pau- freshwater shrimps and prawns in East Asia cidens De Haan, 1884 (Palaemonidae) and (e.g., Thielemann, 1910; Tattersall, 1921; Ko- Neocaridina sp. (Atyidae) at four localities in mai, 1927; Nierstrasz, 1931; Shen, 1936; Iwa- Shikoku and western Honshu. This paper brief- sa, 1947; Karim & Fernando, 1963; Shiino, ly describes T. chinensis and reports on these 1965; Matsumoto, 1973; Delaney, 1989; Yu & collections with a new record of the species Li, 1998; Takeda et al., 2000; Saito, 2011, see from Shikoku and its occurrence on freshwater Table 2). There is as yet scant information on shrimps at the four localities. A list of the the biology of T. chinensis because the previ- known collection localities and hosts of T. chi- ous papers of the species mostly dealt with its nensis is also given based on the literature pub- taxonomy and distributional records. During a lished between 1910 and 2018 and this paper. faunal study of freshwater shrimps in central Received: 2 May 2018. Accepted: 14 Aug 2018. Published online: 28 Sept 2018. 73 KAZUYA NAGASAWA, TADASHI IMAI, HIDETOSHI SAITO ■ Materials and Methods species were recognized in this study. Howev- er, these two species are tentatively reported Shrimp sampling herein as sp. 1 and sp. 2 because the recent tax- Freshwater shrimps were collected using a onomy of shrimps of the genus from Japan is D-shaped hand net (mesh size, 2.5 mm; frame highly confused due to the invasion of alien width, 33 cm; handle length, 60 cm) in Kagawa congeneric species to the country (e.g., Nishi- Prefecture (Shikoku) on 26 October 2014 and no, 2017). Since the propodus of their third pe- Shimane Prefecture (western Honshu) on 22 reiopod is similar in both sexes (cf. Mitsugi et October 2017. The collection localities in al., 2017), both species are not a recently intro- Kagawa Prefecture were a pond in Tsuda Park duced species, Neocaridina davidi (Bouvier, (34°17′37″N, 134°13′58″E, locality 29 in Fig. 1904) and will be reported in a separate article. 2), Tsuda, Sanuki, and the Sakamoto River Isopod-infested shrimps were later transported (34°12′36″N, 134°25′31″E, locality 30 in Fig. to the laboratory at Hiroshima University, Hi- 2), Sakamoto, Higashi-Kagawa, and the collec- gashi-Hiroshima, where isopods were carefully tion localities in Shimane Prefecture were removed using forceps and preserved in 70% Myôji Reservoir (35°27′50″N, 132°48′51″E, ethanol. Isopods were measured for body locality 23 in Fig. 2), Takudani, Izumo, and Ko length (from the anterior margin of the cepha- Reservoir (35°26′21″N, 132°48′43″E, locality lon to the posterior margin of the pleotelson), 24 in Fig. 2), Hirata, Izumo. At each locality, sexed (based on the presence or absence of an submerged vegetation and root masses were appendix masculina arising from the proximal scooped five times to quantitatively collect margin of the endpod of pleopod 2, cf. Del- shrimps. At the two localities in Kagawa Pre- aney, 1989, fig. 34F), and identified. Isopods fecture, shrimps were identified and counted on from Myôji Reservoir were examined for mor- site, and only isopod-infested individuals were phological characters using an Olympus taken and fixed in 10% formalin, while at the SZX10 stereo microscope and an Olympus two localities in Shimane Prefecture, shrimps BX51 light microscope, and drawings were were identified, separated into two groups by made with the aid of a drawing tube fitted on the presence or absence of isopod, and fixed in each of these microscopes. Voucher specimens 10% formalin individually in small plastic of T. chinensis have been deposited in the bags. During the field samplings, we carefully Crustacea (Cr) collection of the National Mu- scooped the shrimps and took firstly the infest- seum of Nature and Science, Tsukuba, Ibaraki ed ones: we found no detached isopod in the Prefecture, Japan (NSMT-Cr 25830 [n＝10] nets. from P. paucidens at a pond in Tsuda Park; NSMT-Cr 25831 [n＝10] from P. paucidens at Laboratory examination Myôji Reservoir). The remaining specimens of Shrimps from the four localities were T. chinensis are retained by the senior author brought to the laboratory at the National Re- (K. N.) for a future morphological study of the search Institute of Fisheries and Environment species from various localities in Japan and of Inland Sea, Takamatsu, where their on-site will be deposited in the same collection. Preva- identification was confirmed and they were lence and intensity of infestation are those de- measured for body length (from the orbital fined by Bush et al. (1997). The scientific edge of the carapace to the posterior margin of names of Japanese shrimps and prawns men- the telson) in mm. In particular, shrimps of the tioned in this paper follow Toyota & Seki atyid genus Neocaridina were carefully ob- (2014). served for morphological features, and two 74 Crustacean Research 47 Crustacean Research 47 TACHAEA CHINENSIS FROM JAPANESE SHRIMPS ■ Results Body slightly elongated, with many chro- matophores scattered on dorsal surface. Cepha- Description of T. chinensis lon small, nearly triangular, anteriorly with The following description of T. chinensis rounded rostrum. Eyes laterally separated. An- (Fig. 1A, Fig. 2) is based on 15 non-ovigerous tennula short, with 8–9 articles (2 peduncle ar- females (4.0–7.5 mm long) from Myôji Reser- ticles and 6–7 flagellum articles); peduncle voir. basal article slightly enlarged, article 2 cylin- drical; flagellum article 1 about as long as pe- duncle article 2. Antenna long, reaching to pe- reonite 4, with 18–19 articles (5 peduncle articles and 13–14 flagellum articles); peduncle articles 4 and 5 subequal. Pereonites 1–4 slightly larger than pereonites 5–7; posterolateral corners of pereonites 4–7 increasing in size posteriorly; pleonite 4 with lateral portions produced posteriorly and ex- Fig. 2. Tachaea chinensis, non-ovigerous female, 6.4 mm Fig. 1. Tachaea chinensis, non-ovigerous female, 7.1 mm long, NSMT-Cr 25831, from Palaemon paucidens in Myôji long, NSMT-Cr 25831, from Palaemon paucidens in Myôji Reservoir, Izumo, Shimane Prefecture, western Japan. Reservoir, Izumo, Shimane Prefecture, western Japan, ethanol- A, cephalon and anterior pereonites (right antenna is not preserved specimen. A, body, dorsal view; B, individual illustrated), dorsal view; B, pleotelson and left uropod (right attached on the lateral side of the carapace of P. paucidens. uropod is not illustrated), dorsal view. Scale bars: 0.5 mm in A Scale bars: 2 mm in A; 3 mm in B. and B. Crustacean Research 47 Crustacean Research 47 75 KAZUYA NAGASAWA, TADASHI IMAI, HIDETOSHI SAITO Table 1. Occurrence of Tachaea chinenis on freshwater shrimps at four localities in western Japan Body length Percent Intensity Locality Prefecture Collection date Shrimp species (mm) prevalence (mean) Pond in Tsuda Park Kagawa 26 October 2014 Palaemon paucidens 16.7–24.4 48.5 (16/33*) 1 (1.0) Paratya improvisa 10.6–17.8 0 (0/4) 0 Neocaridina sp. 1** n.m*** 0 (0/37) 0 Sakamoto River Kagawa 26 October 2014 Palaemon paucidens 17.7–31.7 10.7 (6/56) 1 (1.0) Myôji Reservoir Shimane 22 October 2017 Palaemon paucidens 19.9–28.1 37.9 (11/29) 1–3 (1.4) Neocaridina sp. 1 and sp. 2** 10.0–15.6 0 (0/6) 0 Ko Reservoir Shimane 22 October 2017 Palaemon paucidens 18.7–22.4 57.1 (4/7) 1 (1.0) Neocaridina sp. 1 8.3–22.3 12.5 (1/8) 1 (1.0) * No. infested/examined. ** See the Materials and Methods section for the identication of these species. *** Not measured. tending to pleotelson. Pleotelson semi-triangu- spectively. lar, with 8–9 (mostly 8) robust setae and longer There was no particular relationship between plumose setae on posterior margin.