Host specificity refers to the relationship between freshwater mussels and their fish hosts, which is essential for the reproductive success of this increasingly relevant taxa. Apart from a few species, juvenile morphogenesis is contingent upon an obligate parasitic relationship between freshwater mussel larvae and an appropriate host fish. Host specificity varies considerably with some mussels reliant on one or a few closely related host fish (i.e., specialists), while other species can parasitize a wide range of fish (i.e., generalists). The successful propagation of freshwater mussels in laboratory settings depends on the use of suitable fish hosts. However, in many cases, scientists must rely on alternative hosts when primary hosts are unavailable, unresponsive to captivity, or face environmental challenges that hinder their use (e.g., endangered species). The Alewife Floater (Utterbackiana implicata) has been recognized as a functionally dominant species in the freshwater tidal region of the Delaware River and depends on the spring migration of river herring (such as Alewife and Blueback herring) for successful recruitment. However, in laboratory settings, these fish have shown to be challenging to maintain, leading to high mortality rates during inoculation or prior to excystment. In 2024, scientists at the Philadelphia Water Department’s freshwater mussel hatchery achieved the first documented and successful propagation of U. implicata using hybrid striped bass (Morone saxatilis X Morone chrysops). Metrics of relative infestation, post-inoculation mortality, and yield per fish, far surpassed that of know primary hosts, making hybrid striped bass a potentially effective host for propagation of Alewife Floaters.