The freshwater bivalve Potamilus purpuratus is a large, distinctive
unionid which occurs throughout much of the central and lower
Mississippi River Valley (Cummings & Mayer 1993; Vidrine 1993). It
is also known to occur in tributaries of the Gulf of Mexico east and
west of the Mississippi River (Strecker 1931; Vidrine 1993).
In Texas, this species occurs from the Red River drainage southwest
into the Guadalupe/San Antonio River drainage (Howells et al. 1996).
Strecker (1931) did not report P. purpuratus from the Nueces or Frio
rivers and Murray (1978) did not find it in a survey of Lake Corpus
Christi on the lower Nueces River. Previous reports by Strecker (1931)
of this species from the Devils River near its confluence with the Rio
Grande were found to represent misidentified specimens (R. Neck & C.
Boone, pers. comm.) of the Tampico pearlymussel Cyrtonaias tampicoensis.
Metcalf (1982) did not find this species represented in the fossil
assemblages of the central Rio Grande and Neck & Metcalf (1988) did
not report it from the lower Rio Grande downstream from Falcon
Freshwater mussels not only support important commercial fisheries,
but are among one of the fastest declining groups of animals in North
America (Neves 1993; Williams et al. 1993). Because of this, the staff
of the Texas Parks and Wildlife Department's (TPWD) Heart of the
Hills Research Station began a study of Texas unionid populations in
1992, including statewide distributional surveys. From October 1993
through January 1995, populations of Potamilus purpuratus were found at
several sites outside their previously known ranges. This study
represents an extension of the previously known range of P. purpuratus
in Texas. Voucher specimens are deposited with the holdings of the
Houston Museum of Natural Science (HMNS).
Potamilus purpuratus (Lamarck)
(bleufer, blooper or blue mucket)
Material examined. -- Lake Corpus Christi, Live Oak County, Texas,
5 October 1993, two specimens (HMNS 42487); Amistad Reservoir (near
confluence of Devils River), Val Verde County, Texas, 21 December 1994,
two specimens (HMNS 42486); Middle Concho River upstream from Twin
Buttes Reservoir, Tom Green County, Texas, 3 August 1994, two specimens
Distributional notes. -- Survey work conducted in Lake Corpus
Christi and the Nueces River just upstream of the reservoir in October
1993 revealed that P. purpuratus was one of the most abundant unionid
taxa in the reservoir. It was represented by very small juveniles (<
15 mm shell length, sl) through mature, gravid adults (> 80 mm sl).
However, no large, old adults (> 110 mm sl) were found. Specimens
were morphologically similar to specimens from the central and upper
Colorado River drainage of Texas. Other collections made further
upstream in Choke Canyon Reservoir and the Frio River up and down-stream
of the reservoir, Live Oak and McMullen counties, during 1993 and 1994
period failed to yield any specimens of P. purpuratus. The survey of
Lake Corpus Christi by Murray (1978) was made during drought conditions
when the water level was extremely low. If present at that time,
specimens of P. purpuratus would probably have been found. This suggests
an introduction likely occurred in the late 1970s or 1980s.
Several additional bleufer valves were also collected in December
1994 in Amistad Reservoir near the confluence of the Devils River during
a drawdown which exposed much of the reservoir bottom. A return trip to
the area in January 1995 yielded additional valves as well as three
living specimens. These included relatively small juveniles (< 70 mm
sl) to larger, older adults (> 125 mm sl). Comparison of the Amistad
material to several badly-weathered valves taken by TPWD in January 1992
upstream on the Rio Grande just downstream of San Francisco Creek,
Terrell County, indicated the earlier specimens were bleufers as well.
Other surveys by TPWD in the Rio Grande down-stream of Amistad Reservoir
1992-1995 failed to yield bleufers. Clearly the Amistad population
contained larger, older animals than observed in Lake Corpus Christi.
Absence of P. purpuratus in the fossil record (Metcalf 1982) from the
Rio Grande drainage suggests the Amistad specimens may also represent an
introduction, but at a much earlier date.
Biochemical comparisons. -- Horizontal starch gel electrophoresis
(Morizot & Schmidt 1990) was used to examine tissue samples from Rio
Grande and Nueces River specimens to confirm identification. Enzyme
systems previously found by Neck & Howells (1994) to show
differences between P. purpuratus, P. ohiensis (pink papershell), and P.
amphichaenus (Texas heelsplitter) were examined. These included
glucose-phosphate isomerase (GPI; E.C. 3.1.1), peptidase (PEP; E.C.
3.4.11. or 3.4.13.), superoxide dismutase (SOD; E.C. 126.96.36.199), malate
dehydrogenase (MDH; E.C. 188.8.131.52), and phosphoglucomutase (PGM; E.C.
184.108.40.206). Specimens examined included those from Nasworthy Reservoir,
Twin Buttes Reservoir, and Middle Concho River (Concho River drainage,
Tom Green County); Concho River (Concho County); Mussel Shoal Creek
(Trinity River drainage, San Jacinto County); Lake Buchanan (Colorado
River drainage, Llano County); Little Brazos River (Brazos River
drainage, Robertson County); and B. A. Steinhagen Reservoir (Neches
River drainage, Tyler County) as well as specimens from Lake Corpus
Christi, Nueces River, and Amistad Reservoir. An additional specimen
from the Pascagoula River, Jackson County, Mississippi was also included
in the comparison. Specimens of P. ohiensis from Lake Arrowhead (Red
River drainage, Clay County) and a P. amphichaenus from B. A. Steinhagen
Reservoir were also comparatively examined. No significant
electrophoretic differences were found among any of the specimens of P.
purpuratus and all were distinctly different from P. ohiensis and P.
Remarks. -- Commercial shell fishermen (musselers) have reported
deliberately transplanting unionids from one body of water to another
(Howells 1993) and inadvertent introductions on glochidia-infected
fishes may also occur (Neck 1982). Although Potamilus purpuratus is
sometimes taken for shells or pearls, harvest for these purposes is
generally very minor when compared to that of other commercially more
desirable mussels in Texas (Howells 1993). It is possible that the
transplanting of pearlproducing Tampico pearlymussels may have
inadvertently introduced specimens of P. purpuratus as well because of
similarity in appearance of the two species. The only known host fish
for the glochidia of P. purpuratus is the freshwater drum (Hoggarth
1992). However, freshwater drum (Aplodinotus grunniens) are rarely
stocked as a sport fish or used as live bait. Consequently,
introductions by this method appear unlikely.
Cummings, K. S., & C. A. Mayer. 1993. Field guide to the
freshwater mussels of the midwest. Ill. Natur. Hist. Sur., Manual 5,
Champaign, 194 pp.
Hoggarth, M. A. 1992. An examination of the glochidia-host
relationships reported in the literature for North American species of
Unionidae (Mollusca: Bivalvia). Malacology Data Net 3(1-4):1-30.
Howells, R. G. 1993. Preliminary survey of freshwater mussel
harvest in Texas. Texas Parks and Wildl. Dept. Management Data Ser. 100,
Austin, 30 pp.
Howells, R. G., R. W. Neck & H. D. Murray. 1996. Freshwater
mussels of Texas. Texas Parks and Wildlife Press, Austin, 218pp.
Metcalf, A. L. 1982. Fossil unionacean bivalves from three
tributaries of the Rio Grande. Pp. 43-59, in Proceedings of the
symposium on recent benthological investigations in Texas and adjacent
states (J. R. Davis, ed.). Texas Acad. Sci., Austin. 278 pp.
Morizot, D. C., & M. E. Schmidt. 1990. Starch gel
electrophoresis and histochemical visualization of proteins. Pp. 23-80,
in Electrophoretic and isoelectric focusing techniques in fisheries
management (D. H. Whitmore, ed.). CRC Press, Ann Arbor, Michigan. 350
Murray, H. D. 1978. Freshwater mussels of Lake Corpus Christi,
Texas. Bull. Am. Mala. Union 1978:5-6.
Neck, R. W. 1982. A review of interactions between humans and
freshwater mussels in Texas. Pp. 169-182, in Proceedings of the
symposium on recent benthological investigations in Texas and adjacent
states (J. R. Davis, ed.). Texas Acad. Sci., Austin, 278 pp.
Neck, R. W., & R. G. Howells. 1994. Status survey of Texas
heelsplitter, Potamilus amphichaenus (Frierson, 1898). Texas Parks
Wildl. Dept., Spec. Rept., Austin, 47 pp.
Neck, R. W., & A. L. Metcalf. 1988. Freshwater bivalves of the
lower Rio Grande, Texas. Texas J. Sci., 40(3):259-268.
Neves, R. J. 1993. A state-of-the-unionids address. Pages 1-10, in
Conservation and management of freshwater mussels (K. S. Cummings, A. C.
Buchanan, and L. M. Koch, eds.). Upper Miss. R. Conserv. Comm., St.
Louis, Missouri, 189 pp.
Strecker, J. 1931. The distribution of naiades or pearly
fresh-water mussels of Texas. Baylor Univ. Mus. Bull. 2, Waco, 69 pp.
Vidrine, M. F. 1993. The historical distributions of freshwater
mussels in Louisiana. Gail Q. Vidrine Collectibles, Eunice, Louisiana,
Williams, J. D., M. L. Warren, Jr., K. S. Cummings, J. L. Harris
& R. J. Neves. 1993. Conservation status of freshwater mussels of
the United States and Canada. Fisheries (Bethesda) 18(9):6-22.
Robert G. Howells
Texas parks and Wildlife Department, Heart of the Hills Research
Station HC07, Box 62, Ingram, Texas 78025
RGH at: email@example.com