Biogeography 20. 103–110. Sep. 20, 2018 Discrimination of two freshwater shrimps, Palaemon paucidens De Haan, 1844 and P. sinensis (Sollaud, 1911) using plumose setae of telson and appendix masculina Tadashi Imai 1*, Kazuki Hayashi 2, Masayuki Nakaso 3, Seinen Chow 4, Kenji Nohara 5 and Takakiyo Oonuki 5 1 National Research Institute of Fisheries and Environment of Inland Sea, Japan Fisheries Research and Education Agency, 234 Yashima-higashi, Takamatsu, Kagawa, 761-0111 Japan 2 Kagawa Prefectural Fisheries Experiment Station, 75-5 Yashima-higashi, Takamatsu, Kagawa, 761- 0111 Japan 3 Chlorella Industry Co., Ltd., 1343 Hisadomi, Chikugo, Fukuoka 833-0056, Japan 4 National Research Institute of Fisheries Science, Japan Fisheries Research and Education Agency, 2-12-4 Fukuura, Kanazawa, Yokohama, Kanagawa 236-8648, Japan 5 School of Marine Science and Technology, Tokai University, 3-20-1 Orido, Shimizu, Shizuoka, 424- 8610, Japan Abstract: Live specimens of two freshwater shrimps, Palaemon paucidens De Haan, 1844 and P. sinensis (Sollaud, 1911) can be distinguished from the specific carapace color patterns. However, color pattern of spec- imen preserved in ethanol or diluted formalin slowly fades and is eventually lost. We re-examined previous information and chose the number of plumose setae on distal end of telson and appendix masculina as new identification characters. Number of plumose setae (average, range) was more in P. sinensis (9.0, 4-14) than in P. paucidens (A type, 2.1, 2-3; B type, 2.0, 1-3). Form and lateral setae arrangement of appendix masculina were found to be different between these two species. These characters cannot be applied to females and young males as well as individuals with a malformed telson. Combining these characteristics with those previ- ously described (the presence or absence of a subterminal tooth on the upper edge of rostrum and different eye size etc.) will enable identification ofP. paucidens and P. sinensis even in color faded state more reliable. Key words: appendix masculina; plumose setae of telson; invasive species; Palaemon miyadii; Palaemon paucidens; Palaemon sinensis. Introduction southeastern Siberia and Sakhalin (Holthuis, 1950; Liu et al., 1990; Li et al., 2007; Cai & Dai, 1999; Freshwater shrimp, Palaemon paucidens De Cai & Ng, 2002; Labay, 2011) (Fig. 1b), and before Haan, 1844 is only the native species of the genus 1990 P. sinensis had not been reported from Japan Palaemon inhabiting freshwater areas in Japan (Liu et al., 1990). However, in 2005, P. sinensis was (Hayashi, 2000) (Fig. 1a). Chinese grass shrimp, P. discovered in an inland waterbody located in Shizuo- sinensis (Sollaud, 1911) (formerly known as Palae- ka Prefecture, central Japan (Oonuki et al., 2010). monetes sinensis) is distributed in China, Myanmar, Now P. sinensis is reported from 15 of 47 prefectures ——————————————————————— in Japan (Chow et al., 2018; Environment Division *Corresponding author:[email protected] of the Suginami Ward, 2016; Hasegawa et al., 2016; − 103 − Discrimination of Palaemon paucidens and P. sinensis Tadashi Imai, Kazuki Hayashi, Masayuki Nakaso, Seinen Chow, Kenji Nohara and Takakiyo Oonuki a 130ﾟ E 40ﾟ N c-3 b c-1 c-7 c-2 c-8 a c-4 b c-5 c-6 30ﾟ N 140ﾟ E Fig. 1. Lateral and diagonal views of Palaemon paucidens A type (a), collected at Shin River, Kagawa Prefecture and P. sinensis (b) collected at Hasuike Park, Kochi Prefecture. Fig. 2. Sampling locations of Palaemon paucidens and P. sinensis Scale bars = 10 mm. in Japan. (a) Shin River, Miki Town, Kagawa Prefecture; (b) Kumomo River, Tosashimizu City, Kochi Prefecture; (c-1) central brook in the Mizumoto Park, Katsushika Hiraoka et al., 2018; Imai & Oonuki, 2014, 2017; Ward, Tokyo; (c-2) an unnamed pond, Hamamatsu City, Shizuoka Prefecture; (c-3) Takahashi River, Soja City, Oonuki et al., 2017; Saito, 2017; Saito et al., 2016, Okayama Prefecture; (c-4) Pond in the Takamiyama 2017; Shichiri et al., 2017; Yoshigo & Yoshigo, Park, Tonosho Town, Kagawa Prefecture; (c-5) Pond in the Hasuike Park, Tosa City, Koch Prefecture; (c-6) 2016) (Fig. 2). Howara River, Iwamatsu River System, Uwajima City, P. paucidens is also distributed in China and Ko- Ehime Prefecture; (c-7) Shiota River, Ureshino City, Saga Prefecture; (c-8) Lake Shimoezu (brook in the Suizenji- rea (Li et al., 2007; Kim, 2012), which has been ex- ezuko Park), Kumamoto City, Kumamoto Prefecture. ported to Japan for use as bait (Niwa, 2010; Saito et P. paucidens A and B types, and P. sinensis used in this study were collected at a, b and c-1 - c-8, respectively. al., 2011). Since P. paucidens and P. sinensis which Prefectures where P. sinensis was collected in the previous very closely resemble each other have been imported studies (Chow et al., 2018; Environment Division of the Suginami Ward, 2016; Hasegawa et al., 2016; Hiraoka to Japan without being distinguished, the occurrence et al., 2018; Imai & Oonuki, 2014, 2017; Oonuki et al., of P. sinensis in Japan is thought to have been caused 2010, 2017; Saito, 2017; Saito et al., 2016, 2017; Shichiri et al., 2017; Yoshigo & Yoshigo, 2016) are shown in red. by the imported P. sinensis (Niwa, 2010; Oonuki et al. 2010; Saito et al., 2011). Presence or absence of a mandibular palp used to discriminate P. paucidens upper edge of rostrum (Oonuki et al., 2010), molar and P. sinensis is a key characteristic to divide the process structure of the mandible (Labay, 2011), eye formerly genera Palaemon and Palaemonetes (Chace size (Imai & Oonuki, 2014), the projection shape of & Bruce, 1993; Jayachandran, 2001; Li et al., 2007). distal portion of telson (Hasegawa et al., 2016) and Recently, the genus Palaemonetes was demonstrated color pattern of tail fan (Shichiri et al., 2017) were to be junior synonyms of Palaemon (De Grave & reported to be diagnostic characteristics between the Ashelby 2013). As a reliable, non-lethal identifica- two species. However, the color patterns disappear tion method, Imai & Oonuki (2014) reported that in fixatives, and damaged or malformed individuals live samples of both species could be distinguished may not be identifiable by using a single morpholog- from the specific carapace color pattern. In addition, ical key. presence or absence of subterminal tooth on the We reviewed the morphological characters of − 104 − Discrimination of Palaemon paucidens and P. sinensis Tadashi Imai, Kazuki Hayashi, Masayuki Nakaso, Seinen Chow, Kenji Nohara and Takakiyo Oonuki these two species described previously, and the Nikon) (see Imai & Oonuki, 2014). Upper and lower number of plumose setae on distal end of telson and rostrum teeth were counted. Of upper rostrum teeth, shape and lateral setae arrangement of appendix those on the carapace posterior to the eye orbit was masculina are proposed as novel identification char- counted. Presence and absence of subterminal tooth acters. on the upper edge of rostrum was observed. Accord- ing to Imai & Oonuki (2014), eye length (EL) and Materials and Methods diameter of cornea (DC) were measured from the dorsal side. We investigated the presence or absence Specimens were collected at ten locations in Ja- of a palp on the mandibles in some individuals. pan between 2006 and 2018 (Fig. 2). P. paucidens A We reviewed previous descriptions of P. pauci- type sample was collected in Shin River, Miki Town, dens and/or P. sinensis by Kubo (1938), Holthuis Kagawa Prefecture (a). P. paucidens B type sample (1950; Figs. 14, 20, 21), Kim (1977; Figs. 72, 73), was collected in Kumomo River, Tosashimizu City, Suzuki & Sato (1994; p. 7), Bruce (1994) and Li et Kochi Prefecture (b), and P. sinensis samples were al. (2007; Figs. 65, 70), and found specific differ- collected at central brook in the Mizumoto Park, Kat- ences in the number of plumose setae on distal end sushika Ward, Tokyo (c-1), an unnamed pond, Ham- of telson, and shape and lateral setae arrangement of amatsu City, Shizuoka Prefecture (c-2), Takahashi appendix masculina. The number of plumose setae River, Soja City, Okayama Prefecture (c-3), Pond in between inner spines on the distal end of telson was the Takamiyama Park, Tonosho Town, Kagawa Pre- counted from the dorsal side under stereo micro- fecture (c-4), Pond in the Hasuike Park, Tosa City, scope. In second pleopod of male, length of appen- Kochi Prefecture (c-5), Howara River, Iwamatsu dix masculina and appendix interna, and range of River System, Uwajima City, Ehime Prefecture (c- 6), Shiota River, Ureshino City, Saga Prefecture (c- 7), and Lake Shimoezu (brook in the Suizenji-ezuko Park), Kumamoto City, Kumamoto Prefecture (c- 8). Shrimps were caught using D-shaped hand net (mesh size 2.5 mm; frame width 33 cm; handle length 60 cm). P. paucidens and P. sinensis were di- vided on site according to the difference of carapace color pattern (see Imai & Oonuki, 2014). Collected shrimps were then preserved in 10% formalin or 90% ethanol. Two types (A and B) of P. paucidens were genetically identified (see Chow et al. 2018). These fixed samples were used for morphological examination. Body length (BL, from orbital edge to the distal end of telson) and carapace length (CL, from orbital Fig. 3. Appendix masculina and appendix interna of male second edge to posterior margin of carapace) of samples pleopod. (a) Palaemon paucidens A type, collected at Shin River, Kagawa Prefecture (male, 24.2 mm BL, 6.7 were measured using calipers. Individuals with mm CL); (b) P. sinensis collected at Hasuike Park, Kochi appendix masculina on second pleopod were de- Prefecture (male, 22.3 mm BL, 6.1 mm CL). Measurement position: length of appendix masculina (1-4), length of termined to be male. The numbers of rostrum teeth appendix interna (1-2) and range of setae on appendix were counted under stereo microscope (SMZ1270, masculina (3-4).