Epioblasma capsaeformis, commonly named the oyster mussel, once occupied thousands of miles of stream reaches, but has now been reduced in range to small, isolated populations in a few river reaches. Due to this significant decline in population numbers, a study was conducted to develop a diet for propagating this endangered species under captive conditions. Oyster mussel juveniles were collected from several sites on the Clinch River and sacrificed for gut content and biochemical composition analyses in summer. Feces and pseudofeces from live river-collected juveniles were examined seasonally for algae, detritus, and bacteria to qualitatively determine diet of specimens. Two feeding trials also were conducted in this study to evaluate effect of diet (commercial and non-commercial diets), on growth and survival of oyster mussel juveniles. From examination of gut contents, fecal and pseudofecal samples, it was apparent that algae and a significant amount of detritus (~90%) composed wild juvenile diets. E. capsaeformis juveniles (1-3 y of age) could have fed on particles up to 20 µm in size and seemed they were mostly ingesting particles within the 1.5-12 µm size range. Protein content of sacrificed juveniles ranged from 313 to 884 mg/g and was highly variable. Glycogen content ranged from 49-171 mg/g. Caloric content of four juveniles ranged from 2,935.10 to 4,287.94 cal/g, providing a preliminary baseline range for future energetic studies on freshwater mussels. Growth was significantly higher in those juveniles fed the triple concentration algae-mix (62,076 cells/ml) than all other diets tested in trial 1. Results of both feeding trials indicated that survival of juvenile oyster mussels was enhanced when fed an algal diet supplemented by bioflocs. / Master of Science