The life cycle of freshwater unionid mussels is atypical among bivalves and involves both a free-living adult and a parasitic larva, the glochidium. Following fertilization, developing embryos are incubated in the water tubes of the mother's gills where they may remain for several months before being released into the water column and becoming parasitic on fish. The principal objective of this study is to assess the morphological and physiological changes that occur within the gills of brooding female Anodonta cataracta, an abundant freshwater mussel in North Carolina. During brooding, two of the mussel's four gills become packed with nearly a million glochidia, causing the gills to swell to up to thirty times their non-brooding size. The major goals of the proposed research include quantifying the morphological changes that occur within the marsupial gills, comparing the pumping and filtration dynamics of brooding and non-brooding mussels, determining the effect of brooding on oxygen uptake and oxygen extraction efficiency of mussels, and assessing the activity of the cilia responsible for irrigation both the marsupial and non-marsupial gills. The results will provide a more complete understanding of the reproductive biology of A. cataracta, especially the effect of glochidial brooding and release on the physiology and gill morphology of adult females. This information also may have application for the management and conservation of other freshwater bivalves including threatened and endangered species.
