Early life history information on the federally endangered winged mapleleaf (Quadrula fragosa (Conrad, 1835)) mussel is needed by natural resource managers to improve conservation and propagation programs. We conducted four studies to obtain some of this information. First, we observed Q. fragosa in the St. Croix River, Wisconsin between 1997–2010 and found females brood larvae (glochidia) for a unique period, between 8 September to 8 October at water temperatures ranging between 15–21 °C Second, we tested 67 fish species and Necturus maculosus for their ability to transform glochidia into juveniles. Nearly 30,000 juvenile Q. fragosa were produced, but only on Ictalurus furcatus and I. punctatus. Unlike most mussel species, Q. fragosa glochidia grew 3 to 4-fold while attached. Third, using scanning electron microscopy we were able to distinguish Q. fragosa glochidia height and length from six other mussel species that also produce small glochidia (<120 µm in height). Finally, we recovered 535 juveniles from 15 naturally infested fish species to determine if any were Q. fragosa based on glochidia morphology. We identified one juvenile from an I. punctatus as a Q. fragosa. To improve conservation efforts we suggest monitoring not only Q. fragosa beds but also associated Ictalurus populations, whose ranges may extend beyond mussel populations.