Host Species for Glochidia of the Freshwater Unionid Mussel Lanceolaria Grayana in Tanks
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©The Malacological Society of Japan DOI: http://doi.org/10.18941/venus.78.1-2_57 Short Notes December 25, 201957 Short Notes Host Species for Glochidia of the Freshwater Unionid Mussel Lanceolaria grayana in Tanks Toshishige Itoh1*, Akira Someya2 and Wataru Kakino2 1Enoshima aquarium, 2-19-1 Katase-Kaigan, Fujisawa, Kanagawa 251-0035, Japan; *[email protected] 2Kitasato University School of Veterinary Medicine, 35-1 Higashi-Nijyu-Sanbancho, Towada, Aomori 034-8628, Japan The freshwater unionid mussel Lanceolaria glochidia and juveniles of L. grayana collected in grayana inhabits ponds and rivers in East Asia Okayama Prefecture, Japan. (Japan, Korea, China and Russia: Kondo, 2008; Miura & Fujioka, 2015). Larvae of unionid mussels Materials and Methods (glochidia) are known to parasitize live fish (Itoh et al., 2008; Kondo, 2008; Itoh et al., 2014, 2016). At On June 16, 2018, twelve adult mussels (average the end of their parasitic stage, they metamorphose shell length 89.7 ± 18.6 mm; Fig. 1A) were brought into juveniles and detach from their host to settle from the Asahigawa River basin in Okayama on the riverbed (Fukuhara et al., 1990; Kondo, Prefecture to the research lab at Enoshima Aquarium 2008; Negishi et al., 2008). The typical shape (Kanagawa prefecture) then kept in tanks (filled (subtriangular with a pair of hooks), the size with 0.5–2.0 L water at 22–28°C). Some of them (about 0.24 mm in shell length; about 0.22 mm released glochidia on June 24, 2018. All fish used in shell depth) and some of the host species of for this experiment had been kept in quarantine for the glochidia of L. grayana have previously been more than 10 days before the start of the experiment. examined (Higashi & Hayashi, 1964; Kondo, 1997, Each fish was placed in a tank containing 12 L 2008). Glochidia of L. grayana have been found of water and glochidia (50–100 individuals/L) to parasitize three fish species, the Pale Chub for 30–120 min, to allow the glochidia to attach. (Opsariichthys platypus), Dark Chub (Candidia We previously defined this method as an artificial temminckii) and Amur Goby (Rhinogobius sp.) by parasitization process (Itoh et al., 2016). We tested confirming that they stay on the host fish for seven whether glochidia attach to the following thirteen days (Kondo, 1989). Glochidia of L. grayana and L. fish species: Common Carp (Cyprinus carpio), Rosy oxyrhyncha (a synonym or subspecies of L. grayana Bitterling (Rhodeus ocellatus ocellatus), Dark Chub from Lake Biwa) parasitize several other fish, such as (Ca. temminckii), Field Gudgeon (Gnathopogon the Ayu Sweetfish (Plecoglossus altivelis), Gin-buna elongatus elongatus), Topmouth Gudgeon (Pseudop. (Carassius sp.), another Dark Chub (Ca. sieboldii), parva), Barbel Steed (Hemibarbus barbus), Pike the Topmouth Gudgeon (Pseudorasbora parva) and Gudgeon (Pseudogobio esocinus), Flathead Mullet the Japanese Loach (Misgurnus anguillicaudatus). (Mugil cephalus), Japanese Rice Fish (Oryzias Some of these fish are known to be unionid hosts latipes), Whitelimbed Goby (Acanthogobius (Kondo, 1997, 2008; Kondo et al., 2011) but lactipes), Floating Goby (Gymnogobius urotaenia), glochidia have sometimes been recorded from Short-spined Trident Goby (Tridentiger brevispinis) others that are still not confirmed as hosts. In any and Amur Goby (Rhinogobius sp.). We expected case where the glochidia were able to complete the that glochidia would parasitize all of these species. development stages through to metamorphosis into Because the fish used in our experiment were juveniles, the fish were recognized as suitable host brought from aquaculture sources (though of species (Itoh et al., 2008; Itoh et al., 2014, 2016). unknown origin), we expected there to be little or In this study, we report on suitable host species for no prior glochidia parasitism. 58 VENUS 78 (1–2), 2019 All fishes subjected to the parasitization process glochidia artificially attached are shown in Table 1. described above were then moved to 13 discrete For Ca. temminckii, nine individuals died on tanks, one for each species. Every tank was filled day 7 (July 2, 2018), while one survived until with approximately 6 L of aerated water at 27.7 ± the completion of the experiment (July 7, 2018); 0.3°C, and the water was changed every 1–3 days. 12 glochidia (47.9% individuals infected) were The light/dark regime was not controlled. The fishes observed on days 2–5, and 13 juveniles (52.1% were not fed during these tests. The water from these individuals infected) were observed on days 6–7 tanks was filtered through a plankton net (mesh: in the tank. For A. lactipes, two individuals died 0.1 mm), and glochidia and juveniles of L. grayana on day 2 (June 26), two individuals died on day 4 in the net were counted under a stereoscopic (June 28), two individuals died on day 5 (June 30), microscope at magnifications of 5–40x every 1–3 one individual died on day 9 (July 4), while three days (average 47.6 h) for over 12 days. Numbers of survived until the completion of the experiment glochidia and juveniles that detached from the fishes (July 7); 8 glochidia (24.8% individuals infected) were recorded throughout the experimental period were observed on days 2–5, and 13 juveniles (75.2% for each tank and calculated as an average number individuals infected) were observed on days 6–9 per fish for each tank. in the tank. For Gy. urotaenia, one individual died on day 2 (June 26), while eight survived until the Results and Discussion completion of the experiment (July 7); 8 glochidia (51.1% individuals infected) were observed on days The proportions of glochidia and juveniles are 2–5, and 7 juveniles (48.9% individuals infected) shown in Fig. 1. Details of the fish species that had were observed on days 6–7 in the tank. For T. A B C D Fig. 1. Photomicrographs of adults, glochidium and juveniles of Lanceolaria grayana. A. Living adults. B. Dead glochidium that have detached from the fish body. C. Living juvenile after 6–7 days that have detached from the host body. D. Living juvenile after 13–14 days that have detached from the host body. White arrows indicate the foot. Black arrows and spotted lines indicate brim of glochidial shell. Black scale bar = 1 mm. White scale bar = 0.1 mm. Short Notes 59 Table 1. Details of the fish species had glochidia of Lanceolaria grayana artificially attached. Fish Lanceolaria grayana Standard length Proportion Species Provided (mm) Survived Glochidia Juveniles of juveniles No. Standard No. No. No. from a fish Mean Deviation (%) Cyprinus carpio 8 25.4 3.9 5 9 0 0 Rhodeus ocellatus ocellatus 9 37.0 3.3 8 1 0 0 Candidia temminckii 10 48.6 6.7 1 12 13 52.1 Gnathopogon elongatus elongatus 11 44.5 7.9 2 4 0 0 Pseudorasbora parva 12 44.3 7.3 7 4 0 0 Hemibarbus barbus 4 90.8 10.3 4 82 0 0 Pseudogobio esocinus 5 58.6 11.6 5 6 0 0 Mugil cephalus 9 55.2 22.9 4 17 0 0 Oryzias latipes 16 25.5 2.3 9 1 0 0 Acanthogobius lactipes 10 41.5 6.5 3 8 13 75.2 Gymnogobius urotaenia 9 27.5 1.4 8 8 7 48.9 Tridentiger brevispinis 2 64.8 28.6 1 0 12 100 Rhinogobius sp. 10 32.5 4.5 10 12 0 0 Provided No.: Number. of fish provided to the test. Survivied No.: Number of fish survived until the end of the test. Experimental period: over 12 days (from June 25 to July 7, 2018). brevispinis, one individual died on day 2 (June In our experiment we confirmed that glochidia 26), while one survived until the completion of the completed their parasitic stages and metamorphosed experiment (July 7); 12 juveniles (100% individuals to detached juveniles on Ca. temminckii, A. lactipes, infected) were observed on days 6–7 in the tank. For Gy. urotaenia and T. brevispinis. These fish were the remaining nine species, glochidia were observed thereby identified as suitable hosts for the glochidia on days 2–5, but no juveniles were observed in the of L. grayana in tanks. However, our study has some tank. limitations: only a limited number of fishes were Throughout our experiment, all recovered used for the experiment, and not all the glochidia glochidia that detached from bodies of fishes before could be counted because some of the host fish metamorphosis to juvenile were dead; the shells of died during the tests. Nonetheless, our findings glochidia (the length: average 0.21 ± 0.01 mm, the are promising, and this topic should be extensively depth: average 0.19 ± 0.01 mm, the width: average studied in the future. Our finding of new host species 0.14 ± 0.01 mm for four individuals) were light will help clarify some aspects of the ecology of brown and closed (Fig. 1B). Most of the juveniles unionid mussels. that successfully metamorphosed and detached from the hosts were alive; they were opening and closing Acknowledgements: The authors wish to thank their shells and moving by stretching and contracting T. Oyama (Enoshima Aquarium) for improvement their foot (Figs 1C, D). Their bodies were dark of this English manuscript, Y. Hori (Enoshima brown and equal in size to that of the glochidia, and Aquarium), T. Takeshima (Enoshima Aquarium) they retained their glochidial shells (Figs 1C, D). and K. Hori (Enoshima Aquarium) for their support Juveniles that had detached from the hosts survived during this study. for about two weeks. The prodissoconch shell was grown into the glochidial shell. References Currently, only three fish (Op. platypus, Ca.