Abundance of Host Fish and Frequency of Glochidial Parasitism in Fish Assessed in Field and Laboratory Settings and Frequency of Juvenile Mussels or Glochidia Recovered from Hatchery-Held Fish, Central andnSoutheastern Texas, 2012–13.

摘要

In 2012–13, the U.S. Geological Survey (USGS), in cooperation with the U.S. Fish and Wildlife Service (USFWS), completed the first phase of a two-phase study of mussel host-fish relations for five endemic mussel species in central and southeastern Texas that were State-listed as threatened on January 17, 2010: (1) Texas fatmucket (Lampsilis bracteata), (2) golden orb (Quadrula aurea), (3) smooth pimpleback (Quadrula houstonensis), (4) Texas pimpleback (Quadrula petrina), and (5) Texas fawnsfoot (Truncilla macrodon). On October 6, 2011, the USFWS announced the completion of a status review and determined that the five mussel species warranted listing under the Endangered Species Act; however, listing of these species at that time was precluded by higher priority listing actions, and currently (December 2014), they remained unlisted. Freshwater mussels are long-lived, sedentary organisms that spend their larval stage as obligate parasites on the gills or fins of fishes, and many of these larvae, which are referred to as “glochidia,” can survive only on a narrow range of host-fish species. Results from both study phases are likely to provide information useful for propagation of rare mussels, reintroduction of host fish, population and reproduction monitoring, habitat restoration and enhancement, and adaptive management. The abundance of host fish, frequency of parasitism in fish, and frequency of juvenile mussels or glochidia recovered from hatchery-held fish was assessed by collecting fish and mussels at 14 sites distributed among seven streams in central and southeastern Texas (juvenile mussels and glochidia were not differentiated in hatchery-held fish). All fish collected and assessed in this study were wild-caught. Qualitative surveys of the resident mussel communities were made, focusing on the five candidate species. A subsample (3 percent in 2012 and 19 percent in 2013) of the fish collected during aquatic biota surveys was submitted to the USFWS San Marcos National Fish Hatchery and Technology Center to collect juvenile mussels and glochidia recovered from the host fish, which were held for 28 days in holding tanks to allow time for most of the attached glochidia to release from the gills of the fish after transforming into juvenile mussels. All fish not sent to the hatchery were assessed for glochidia in the field or in the USGS Texas Water Science Center laboratory in Austin, Tex. Juvenile mussels and glochidia that were recovered from fish at the hatchery were submitted for use in the second phase of this study, the development of deoxyribonucleic acid (DNA) identification keys to determine mussel and host-fish relationships through DNA-based molecular identification (DNA typing of the juvenile mussels and glochidia). Reporting on the results of DNA-based molecular identification research is beyond the scope of this report.