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2009 SOUTHEASTERN NATURALIST 8(1):19–22
Fish Hosts and Conglutinates of the Pyramid Pigtoe
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.
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
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
20 Southeastern Naturalist Vol. 8, No. 1
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.
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 fish juveniles Days to
Species infested recorded transform
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) − −
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) − −
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.
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
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
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).
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