Crustacean Research 2020 Vol.49: 221–223 ©Carcinological Society of . doi: 10.18353/crustacea.49.0_221 New host and third western Pacific Ocean records for Nerocila trichi- ura (Isopoda: Cymothoidae), a skin parasite of flyingfishes

Kazuya Nagasawa

Abstract.̶ An ovigerous female of the cymothoid isopod Nerocila trichiura (Miers, 1877) was collected from the isthmus of doederleinii (Steindachner, 1887) (: Exocoetidae), in Kowaura Bay, Mie Prefecture, central Japan. This represents the third record of N. trichiura from the western Pacific Ocean, and C. doederleinii is a new host of the isopod. A skin wound caused by the isopod was found at attachment site.

Key words: marine parasite, isopod, cymothoid, Cheilopogon doederleinii

The cymothoid isopod Nerocila trichiura Prefecture, it was thawed, fixed and preserved (Miers, 1877) is a skin parasite of flyingfishes in 70% ethanol, and examined using an Olym- (Beloniformes: Exocoetidae) and widely oc- pus SZX10 stereo microscope. The specimen curs in the tropical and middle-latitude waters of N. trichiura has been deposited in the Crus- of the world oceans (Nagasawa & Isozaki, tacea (Cr) collection of the National Museum 2019; Ravichandran et al., 2019). While N. of Nature and Science, Tsukuba, Ibaraki Pre- trichiura has not been reported from the east- fecture (NSMT-Cr 28349). The scientific ern Pacific Ocean, two records of the species names of fishes mentioned in this paper follow exist from the western Pacific Ocean, where it Froese & Pauly (2019). was first reported in 1884 from the Philippines The ovigerous female of N. trichiura was (Schioedte & Meinert, 1884) and much later found attached to the isthmus of C. doederlei- recorded from Japan (Nagasawa & Isozaki, nii (302 mm TL) (Fig. 1A, B). The female 2019). Recently, an ovigerous female of isopod lacked the left uropod, measuring 31.9 mm was collected by Susumu Isozaki, a fisherman body length (from the anterior extremity of the and amateur scientist, from Cheilopogon doed- cephalon to the posterior end of the pleotelson) erleinii (Steindachner, 1887), in coastal Pacific and 12.7 mm maximum body width (across the waters of central Japan and sent to me for iden- widest pereonite). In Japan, N. trichiura was tification. The specimen is identified as N. recently described using an ovigerous female trichiura and reported herein as its third record from the same locality (Nagasawa & Isozaki, from the western Pacific Ocean. 2019). The specimen of N. trichiura collected The infected fish was caught on 26 June (Fig. 1D–F) is characterized by the body 2.5 2020 with a set net installed in Kowaura Bay times as long as greatest width, widest at pere- (the western North Pacific) off Maruwa onite 6; cephalon anterior margin almost hori- (34°13′33″N, 136°29′00″E), Minami-Ise, Mie zontal but slightly concave; eyes slightly visi- Prefecture. After the fish was identified using ble; pereonite 1 anterior margin concave; Nakabo (2013), photographed, and measured pereonites 1–6 increasing in width; coxae 6 for total length (TL, mm), the isopod was care- and 7 longer than 1–4; all pleonites visible; fully taken and frozen with sea water. Later, at pleonite 1 widest; pleonites 2–5 decreasing in the Aquaparasitology Laboratory, Shizuoka width; ventrolateral margins of pleonites 1 and

Received: 29 Sept 2020. Accepted: 12 Oct 2020. Published online: 6 Nov 2020. 221 KAZUYA NAGASAWA

Fig. 1. Nerocila trichiura, ovigerous female, NSMT-Cr 28349, and its host, Cheilopogon doederleinii, from Kowaura Bay, Mie Prefecture, central Japan. A, host infected by isopod (arrow); B, isopod attached to isthmus of host; C, wound caused by isopod at attachment site (scars indicated by arrowheads); D, whole body, dorsal view; E, cephalon and pereonite 1, dorsal view; F, pleotelson and right uropod, dorsal view. Scale bars: A, 10 cm; B, 20 mm; C, D, 10 mm; E, 2 mm; F, 3 mm. Three photographs (A–C) were taken by Susumu Isozaki.

2 posteriorly directed and acute; pleotelson lat- cephalon and anterior marginal part of pereon- eral margins curving to medial triangular point; ite 1 were inserted into the host tissues (Fig. uropod rami extending far beyond medial point 1B). A circular wound (ca. 11 mm in diameter), of pleotelson; exopod more slender and much where the muscles were exposed to water and longer than endopod. four pairs of distinct scars were present, was The known hosts of N. trichiura are all fly- formed under pereonites 1–5 (Fig. 1B, C). A ingfishes (Exocoetidae), including Exocoetus similar wound was reported from Cypselurus volitans Linnaeus, 1758, an unidentified spe- hirai infected by N. trichiura caught in the cies of Exocoetus, Cheilopogon nigricans same locality (Nagasawa & Isozaki, 2019). As (Bennet, 1840), Cypselurus hiraii Abe, 1953, stated by Nagasawa & Isozaki (2019), the iso- and Parexocoetus mento (Valenciennes, 1847) pod’s feeding on and deep insertion of the pe- (Ravichandran et al., 2019; see Nagasawa & reopod’s dactyli to the host skin are considered Isozaki, 2019 for the literature). Cheilopogon to have induced such wounds at the attachment doederleinii is herein regraded as a new host of site. N. trichiura and represents, following Cypselu- I thank Susumu Isozaki for providing me rus hiraii, the second host of the isopod in Ja- with the specimen of N. trichiura and photo- pan. As N. trichiura is not a strictly host-spe- graphs used in this paper. I am grateful to the cific parasite, the species may be discovered captain and crews of the fishing vessel Ryosyo- from other species of flyingfishes in Japanese maru for their help with fish sampling. I also waters, where 28 species of the Exocoetidae extend my thanks to an anonymous reviewer are known to occur (Motomura, 2020). for useful comments, in particular on host The ovigerous female of N. trichiura was identification, to improve the manuscript. oriented forward at its attachment site, and its

222 Crustacean Research 49 CYMOTHOID ISOPOD FROM THE WESTERN

■ Literature Cited fish parasitic isopod family Cymothoidae Leach, 1818 (Crustacea: Isopoda: Cymot- Froese, R., & Pauly, D. (eds.), 2019. FishBase. hooidea) of . Zootaxa, 4622: 1–99. World Wide Web electronic publication. Schioedte, J. C., & Meinert, F., 1884. Symbolæ www.fishbase.org, version (12/2019) [ac- ad monographiam cymothoarum crustaceo- cessed 23 September 2020] rum isopodum familiæ. IV. Cymothoidæ. Motomura, H., 2020. List of All Japan’s Fish Trib. II. Cymothoinæ. Trib. III. Livonecinæ. Species. Current Standard Japanese and Sci- Naturhistorisk Tidsskrift, Kjøbenhavn, 14: entific Names of All Fish Species Recorded 221–454, pls. VI (Cym. XXIV)–XVIII from Japanese Waters. 560 pp. Kagoshima (Cym. XXXVI). University Museum, Kagoshima. [In Japa- nese with English title] Addresses Nagasawa, K., & Isozaki, S., 2019. New record (KN) Graduate School of Integrated Sciences of a marine fish parasite Nerocila trichiura for Life, Hiroshima University, 1–4–4 (Crustacea: Isopoda: Cymothoidae) from Ja- Kagamiyama, Higashi-Hiroshima, Hiroshima pan, with its confirmed distribution in the 739–8528, Japan western North Pacific Ocean. Species Diver- sity, 24: 195–201. (Present address) Aquaparasitology Laboratory, Nakabo, T., (ed.), 2013. Fishes of Japan with Pic- 365–61 Kusanagi, Shizuoka 424–0886, Japan torial Keys to the Species. Third Edition. 2428 pp. Tokai University Press, Hadano. [In Japanese with English title] E-mail address Ravichandran, S., Vigneshwaran, P., & Ramesh- [email protected] kumar, G., 2019. A taxonomic review of the

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