G. Thomas Watters

SMALL DAMS AS BARRIERS TO FRESHWATER MUSSELS (BIVALVIA, UNIONOIDA) AND THEIR HOSTS

Abstract The distributions of two unionoids (fragile papershell Leptodea fragilis and pink heelsplitter Potamilus alatus) were examined in five North American Midwest river systems in relation to the location of dams on the rivers. These dams were non-navigational (without locks), lacked fish ladders, and varied in height from 1 to 17·7 m. Both species were restricted in their distribution to the river downstream of the dams. This suggests that the host fish(es) of these species was unable to move upstream of these obstacles. Both unionoids are believed to parasitize the freshwater drum Aplodinotus grunniens. Several endangered unionoid species also may use this fish, or other dam-limited fishes, as hosts. Dams, even lowhead structures, may contribute to the overall depletion of unionoids by artificially restricting their distributions and isolating populations from each other. Management practices for endangered fishes and mussels must take into account these physical obstacles.

Patterns of Vertical Migration in Freshwater Mussels (Bivalvia: Unionoida)

ABSTRACT The vertical migration patterns of eight freshwater mussel species were studied in outdoor enclosures. Individual experiments lasted from nine to 20 months, during which time mussels were observed three times per week. The mussels displayed two patterns of seasonal vertical migration; in both patterns populations of each species surfaced during spawning in spring and eventually reburied in autumn. These activities coincided with increasing spring water temperatures and decreasing autumn water temperatures, as well as increasing and decreasing durations of daylight. One group of species displayed a unimodal annual pattern, where most of the population surfaced in the spring and remained there until autumn. The second group displayed a bimodal pattern in which the population reburied itself after emerging in spring but then resurfaced and remained at the surface until autumn. We have not been able to associate this second emergence with any biological function. Patterns did not follow generic or subfamilial lines.

The Evolution of the Unionacea in North America, and Its Implications for the Worldwide Fauna

“The distribution in space of the uniones of the continental interior has been shown to be in many respects very peculiar” Keyes 1894:26.

Metamorphosis of Freshwater Mussel Glochidia (Bivalvia: Unionidae) on Amphibians and Exotic Fishes

Abstract This study determined that inexpensive and easily maintained amphibians and exotic fishes could act as hosts for two species of native North American unionid mussels, and bypass the need to identify native hosts when the object is to culture mussels. Two mussel species, Lampsilis cardium and Utterbackia imbecillis, were used to parasitize 42 exotic fishes and seven potential nonpiscine host species. Nonpiscine hosts included amphibians and decapod crustaceans. Lampsilis cardium successfully metamorphosed on six species of exotic fishes, as well as on larval tiger salamanders. Utterbackia imbecillis successfully metamorphosed on 30 species of exotic fishes and all four amphibian species tested. No glochidia metamorphosed on crustaceans. Successful metamorphosis on amphibians indicates that mussel zoogeography may be more complicated than previously thought. Using surrogate hosts may be a valuable alternative to natural hosts in laboratory culture of mussels.

Shedding of Untransformed Glochidia by Fishes Parasitized by Lampsilis fasciola Rafinesque, 1820 (Mollusca: Bivalvia: Unionidae): Evidence of Acquired Immunity in the Field?

ABSTRACT Fifteen fish species were exposed to glochidia from the freshwater mussel Lampsilis fasciola. Mussels and fishes were collected in the Big Darby Creek system in Ohio. All fishes began shedding untransformed glochidia within 24 hrs of exposure and continued for approximately eight days. On Day 19, after two weeks of inactivity, rosefin shiner began to shed numerous untransformed glochidia again. This release lasted 24 days. Rainbow darter began shedding untransformed glochidia on Day 25 and continued to do so for 14 days. No transformation occurred on either fish species. We believe this reaction was due to an acquired immunity and may represent the first report of this phenomenon in wild-caught fishes.

Analysis and cytologic characterization of hemocytes from freshwater mussels (Quadrula sp.).

BACKGROUND Freshwater mussels are among the most endangered taxa in North America and minimally invasive techniques to evaluate their health are needed. OBJECTIVE The objective of this study was to develop a standardized approach for identifying and enumerating the cellular components of freshwater mussel hemolymph. METHODS Hemocyte clumping, total hemocyte count, and hemocyte morphology were compared in untreated hemolymph or hemolymph treated with formalin, sodium citrate, sodium heparin, EDTA, water, or l-cysteine. Morphology was then used to categorize hemocytes and perform a 100-cell differential. RESULTS Treatment with formalin or >25 mg/mL l-cysteine reduced hemocyte clumping, although only formalin significantly increased the total hemocyte count. However, formalin also induced crenation that impaired hemocyte identification. Both EDTA and sodium citrate-induced hemocyte degranulation while sodium citrate and >40 mg/mL l-cysteine-induced cell lysis. Hemocytes could be categorized into 2 groups of granulocytes (eosinophilic or basophilic) and 2 groups of agranulocytes (large or small) for performing a cytologic differential. The differential was not significantly altered by anticoagulant treatments providing cell morphology was adequate for obtaining a differential. Eosinophilic granulocytes predominated (59%) with fewer large agranulocytes (27%) and basophilic granulocytes (13%). Small agranulocytes comprised 2% of the total population. CONCLUSIONS No single treatment provided an optimal method to evaluate freshwater mussel hemolymph. Maximal hemocyte counts were obtained following formalin treatment. l-cysteine reduced clumping and maintained hemocyte morphology for performing a cytologic differential. These techniques provide a standardized approach for the hematologic evaluation of freshwater mussels.

Nontargeted metabolomics reveals biochemical pathways altered in response to captivity and food limitation in the freshwater mussel Amblema plicata

Effective conservation of freshwater mussels (Mollusca: Bivalvia: Unionidae), one of the most endangered groups of animals in North America, is compromised by limited knowledge of their health. We address this gap in knowledge by characterizing the metabolic profile of Amblema plicata in the wild and in response to captivity and food limitation. Eight mussels brought into captivity from the wild were isolated for 18 days without a food source. Hemolymph samples were taken prior to, and 9 and 18 days after the start of the experiment; these samples were analyzed by gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry. We detected and identified 71 biochemicals in the hemolymph of freshwater mussels; of these, 49 showed significant changes during captivity and/or food limitation (p<0.05). Fasting resulted in severe metabolite depletion. Captive (but fed) mussels experienced changes similar to (albeit less severe than) fasting mussels, suggesting that mussels may experience nutritional deficiency under common captive conditions. A. plicata responded to food limitation stress by preferentially using energy reserves for maintenance rather than growth. Carbohydrate and energy metabolism exhibited down-regulation in captive, food-limited, and wild mussels. Lipid metabolism was up-regulated in captive/food-limited mussels and unchanged in wild mussels. Amino acid metabolism was up-regulated in wild mussels and down-regulated in captive/food-limited mussels. Nucleotide metabolism was up-regulated in the wild mussels, down-regulated in food-limited mussels, and unchanged in captive mussels. The different responses between treatment groups suggest potential for nucleotide metabolism as a biomarker of health status for freshwater mussels.

Dams, Zebras, and Settlements: The Historical Loss of Freshwater Mussels in the Ohio River Mainstem

Abstract: The decline of the freshwater mussel fauna of the Ohio River, U.S.A. is compared to the dates of service of the existing dams, the arrival of the exotic zebra mussel, and the presence of urban centers on the mainstem. Based upon historical records we know that most pools supported 20–50 species of mussels; today many have fewer than ten. The results presented here show a mixed effect of the dams on the mussel fauna, ranging from marked deleterious effects in Hannibal, McAlpine, and Smithland pools to comparatively little effect in pools such as Dashields, Greenup, and Markland. In nearly all cases, the most dramatic declines in mussels were associated with the arrival of zebra mussels in the Ohio River in 1991. Pools with significant urban centers often had a loss of diversity well before the construction of dams or the arrival of zebra mussels; these losses are attributed to water quality problems associated with urban centers. Mussel diversity has thus declined in the Ohio River as the result of a three-fold problem: loss of water quality, existing dams, and zebra mussels.

The Freshwater Mussels (Unionidae) of Twin Creek, Southwest Ohio

ABSTRACT We surveyed the mussel fauna of Twin Creek in southwest Ohio and examined its distribution relative to several selected environmental parameters. Unionid presence was determined with visual searches at 36 sites across 76 km in four counties. Fifteen species from the subfamilies Anodontinae, Ambleminae, and Lampsilinae were recorded, with nine species found alive at 17 of the 36 sites. Mussel species richness and species composition agree in general with historical studies of Twin Creek and other streams in the Great Miami River watershed, although some species have declined or been extirpated. The subfamily Ambleminae was almost completely missing from the area. The presence of three species only as dead and relic shells also may indicate a loss of species richness over the last few decades. Species richness values from Twin Creek were lower than for streams in central and northeastern Ohio.

Distribution and Prevalence of Glochidia-Infested Wild-Caught Fishes at a Muskingum River Site in Southeastern Ohio

ABSTRACT Wild-caught fishes were examined from the Muskingum River in southeastern Ohio for the prevalence of glochidial infestation. Weekly collections over a 24-hour period for one year yielded 22 fish species (2,097 individuals). Six species (27%) were infested with glochidia—channel catfish, freshwater drum, gizzard shad, orange-spotted sunfish, bluegill, and hybrid Morone. Infestations were found during the months of March through August, and no infested fish were found during the months of September through February. The month with the highest number of infested fish species was August, and the lowest number occurred in April. The percentage of all individuals infested with glochidia was very low, 2.5%, but was similar to that reported for other rivers and higher that reported for most lakes. The percentage of all fish species infested was lower than those reported for rivers but still greater than the results for lakes. The impounded study site seems to fall between a unregulated river and a lake in terms of its prevalence of infested fishes. The glochidia were over-dispersed in the host populations; 100% of the infested species had 50% or fewer of their individuals infested. The mussel faunal assemblage at the study site appeared to be driven primarily by the presence of a single fish, freshwater drum, and not by the relative abundance of the fish species available.