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Fish Hosts and Conglutinates of the Pyramid Pigtoe (Pleurobema rubrum)
J. Jacob Culp, Adam C. Shepard, and Monte A. McGregor

Southeastern Naturalist, Volume 8, Number 1 (2009): 19–22

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2009 SOUTHEASTERN NATURALIST 8(1):19–22 Fish Hosts and Conglutinates of the Pyramid Pigtoe (Pleurobema rubrum) J. Jacob Culp1,*, Adam C. Shepard1, and Monte A. McGregor1 Abstract - Little information exists on the life history of Pleurobema rubrum (Pyramid Pigtoe). We determined fish hosts and made observations on the conglutinate release of Pyramid Pigtoe. From 2003 to 2005, fourteen Pyramid Pigtoe individuals were collected during mussel sampling on the Green River, KY and held in captivity. In June of 2006, one captive female was observed releasing conglutinates (water temperature was 22.5 oC). Nine fish species were exposed to Pyramid Pigtoe glochidia. After 12–15 days, transformation of glochidia to juveniles occurred on 4 species from the family Cyprinidae: Cyprinella spiloptera (Spotfin Shiner), Erimystax dissimilis (Streamline Chub), Lythrurus fasciolaris (Scarlet Shiner), and Notropis photogenis (Silver Shiner). All 4 are potentially natural hosts and Spotfin Shiner appears to be the most suitable host fish for propagation purposes. Introduction Pleurobema rubrum (Rafinesque) (Pyramid Pigtoe) is a freshwater mussel that occurs sporadically in large rivers in the Ohio and Mississippi River systems and has been extirpated from a large proportion of its historical range. It is listed as threatened by Williams et al. (1993) and is considered imperiled or critically imperiled in states where extant populations still occur. Kentucky is likely to have the healthiest populations of this species located throughout the mid- to lower Green River system (Nature Serve 2008). There are 33 species in the genus Pleurobema, including 12 federally endangered species. Several Pleurobema species have been documented to be short-term or tachytictic brooders; spawning in spring or early summer and releasing all glochidia by the end of the same summer (Baker 1928, Layzer et al. 2003, Ortmann 1919). Currently, fish hosts are unknown for most of the species in this genus. As part of the Kentucky Department of Fish and Wildlife Resources initiative to restore endangered and imperiled species, Pyramid Pigtoe were collected from the Green River and kept for propagation purposes at the Center for Mollusk Conservation in Frankfort, KY. Little life-history information exists for the Pyramid Pigtoe, and captivity in a semi-natural system allowed year-round observations to be made. The purpose of this study was to discover any fish hosts of Pyramid Pigtoe, and in particular, identify hosts most effective for use in propagation. 1Kentucky Department of Fish and Wildlife Resources, Center for Mollusk Conservation, 3761 Georgetown Road, Frankfort, KY 40601. *Corresponding author - jacob.culp@ky.gov. 20 Southeastern Naturalist Vol. 8, No. 1 Methods From 2003 to 2005, fourteen Pyramid Pigtoe individuals were collected during mussel sampling throughout the upper Green River, KY. All individuals collected were examined for gravidity, measured, and tagged. They were then placed into a gravity-fed, fl ow-through raceway system that maintains natural water temperatures and light cycles to facilitate reproduction. On June 15, 2006, a single female Pyramid Pigtoe was observed releasing conglutinates. Glochidia were collected from conglutinates and a subsample was checked for viability by adding a few grains of iodized salt. Nine fish species, previously collected and held in aquaria, were then selected to test as suitable hosts. The fish were selected based on the following criteria: distribution, habitat preferences, and status as known host fish of other Pleurobema species. Fish were anesthetized with MS-222, and approximately 100 to 150 glochidia were pipetted directly onto the gill filaments of each fish. Fish were held in a modified, multi-tank, recirculating system (AHAB Aquatic Habitats, Inc.®, Apopka, FL). Each tank received a continuous supply of water, and the overfl ow drained through a filter cup with a 150-um screen. After 10 days, screens were rinsed into a petri dish and checked for juveniles. Screens were then checked daily for another 7 days to collect all juveniles and determine host fish. Results Individuals of Pyramid Pigtoe collected from the Green River had total lengths ranging from 33 to 100 mm (mean = 66.5 mm), and none were gravid at the time of collection. The single female that released conglutinates in captivity was 79 mm. Approximately 50 white conglutinates (15–20 mm long and about 5 mm wide) were released on June 15, 2006 at about 1400 hours over a 10-minute interval. Conglutinates contained few glochidia Table 1: Results of Pleurobema rubrum (Pyramic Pigtoe) host fish trials. Numbers in parentheses represent number of fish surviving entire study. No. of No. of fish juveniles Days to Species infested recorded transform Cyprinidae Cyprinella spiloptera (Cope) (Spotfin Shiner) 3 (3) 79 12–15 Erimystax dissimilis (Kirtland) (Streamline Chub) 3 (3) 23 13–15 Hybopsis amblops (Rafinesque) (Bigeye Chub) 3 (3) − − Lythrurus fasciolaris (Gilbert) (Scarlet Shiner) 4 (3) 20 12–15 Notropis photogenis (Cope) (Silver Shiner) 3 (1) 4 13–15 Phenacobius uranops Cope (Stargazing Minnow) 1 (1) − − Percidae Etheostoma bellum Zorach (Orangefin Darter) 1 (1) − − Etheostoma maculatum Kirtland (Spotted Darter) 1 (0) − − Etheostoma rafinesquei Burr and Page in Page and Burr 1 (1) − − (Kentucky Darter) 2009 J.J. Culp, A.C. Shepard, and M.A. McGregor 21 (10 were measured: mean length = 162 μm, mean height = 173 μm) and consisted mostly of unfertilized eggs. All conglutinates combined totaled an estimated 2500 glochidia. Water temperature at the time of conglutinate release in fl ow-through raceways was recorded at 22.5 oC. Of the 9 species of fish that were exposed to glochidia, 4 species produced 126 juveniles of Pyramid Pigtoe (Table 1). Successful transformation of Pyramid Pigtoe glochidia occurred on Cyprinella spiloptera (Spotfin Shiner), Erimystax dissimilis (Streamline Chub), Lythrurus fasciolaris (Scarlet Shiner), and Notropis photogenis (Silver Shiner). Juveniles were found in screens starting on day 12 of the study and continued to be located through day 15 at water temperatures between 21–22 oC. Discussion Species in the genus Pleurobema are generally considered to be shortterm brooders (spawn in spring and release glochidia in summer). The single female released all conglutinates on a single day in mid-June, further evidence that Pyramid Pigtoe is a short-term brooding species. Based on time of collection (2003–2005) and the time of conglutinate release (June 2006), it appears that spawning and fertilization occurred in captivity. The lack of gravid females found during sampling further implies captive reproduction. The conglutinates released contained few viable glochidia and consisted mostly of unfertilized eggs. This latter life-history trait has been observed among other Pleurobema species as well (Layzer et al. 2003, Lefevre and Curtis 1912). Four fish hosts from the family Cyprinidae were identified for Pyramid Pigtoe. This finding coincides with those for other species in the genus Pleurobema, many of which use at least one cyprinid species as a host (Haag and Warren 1997, 2003, Hove and Neves 1994; Hove et al. 1997; Weaver et al. 1991). All 4 fish species identified as hosts are common in the current range of Pyramid Pigtoe, and all but Scarlet Shiner are generally associated with the large river habitat of the Pyramid Pigtoe in Kentucky (Burr and Warren 1986). Based on availability, ease of handling, and number of juveniles produced, Spotfin Shiner is likely the best current host for propagation purposes. Acknowledgments We would like to thank the following people for their various contributions to this study: Kristina Best, Wendell Haag, Leroy Koch, Matt Thomas, and Fritz Vorisek. This research was partially funded by the United States Fish and Wildlife (Section 6 Grant). Literature Cited Baker, F.C. 1928. The freshwater Mollusca of Wisconsin. Part II. Pelecypoda. Bulletin of the Wiscosin Geological and Natural History Survey, University of Wisconsin, Madison, WI. 70(2) 495 pp. 22 Southeastern Naturalist Vol. 8, No. 1 Burr, B.M., and M.L. Warren. 1986. A Distributional Atlas of Kentucky Fishes. Kentucky Nature Preserves Commission Scientific and Technical Series 4, Frankfort, KY. 398 pp. Haag, W.R., and M.L. Warren. 1997. Host fishes and reproductive biology of 6 freshwater mussel species from the Mobile Basin, USA. Journal of the North American Benthological Society 16(3):576–585. Haag, W.R., and M.L. Warren. 2003. Host fishes and infection strategies of freshwater mussels in large Mobile Basin streams, USA. Journal of the North American Benthological Society 22(1):78–91. Hove, M.C., and R.J. Neves. 1994. Life history of the endangered James SpinyMussel, Pleurobema collina (Conrad, 1837) (Mollusca: Unionidae). American Malacological Bulletin 11(1):29–40. Hove, M.C., Engelking, R.A., Peteler, M.E., Peterson, E.M., Kapuscinski, A.R., Sovell, L.A., and E.R. Evers. 1997. Suitable fish hosts for glochidia of four freshwater mussels. Pp. 21–25, In K.S. Cummings, A.C. Buchanan, C.A. Mayer, and T.J. Naimo (Eds.). Conservation and Management of Freshwater Mussels II. Proceedings of a UMRCC Symposium, 16–18 October 1995, St. Louis, MO. Layzer, J.B., B. Adair, S. Saha, and L.M. Woods. 2003. Glochidial hosts and other aspects of the life history of the Cumberland Pigtoe (Pleurobema gibberum). Southeastern Naturalist 2(1):73–84. Lefevre, G., and W.C. Curtis. 1912. Studies on the reproduction and artificial propagation of fresh-water mussels. US Bureau of Fisheries Bulletin 30:105–201. Nature Serve. 2008. Nature Serve explorer database. Available online at http://www. natureserve.org. Accessed March 2008. Arlington, VA. Ortmann, A.E. 1919. A monograph of the naiades of Pennsylvania. Part III: Systematic account of the genera and species. Memoirs of the Carnegie Museum 8(1). 384 pp. Weaver, L.R., G.B. Pardue, and R.J. Neves. 1991. Reproductive biology and fish hosts of the Tennessee clubshell Pleurobema oviforme (Mollusca: Unionidae) in Virginia. American Midland Naturalist 126(1):82–89. Williams, J.D., M.L. Warren, Jr., K.S. Cummings, J.L. Harris, and R.J. Neves. 1993. Conservation status of freshwater mussels of the United States and Canada. Fisheries 18(9):6–22.