Novel technique to identify large river host fish for freshwater mussel propagation and conservation

Abstract

Skipjack Herring (Alosa chrysochloris) has long been proposed as the sole host for Reginaia ebenus (Ebonyshell) and Elliptio crassidens (Elephantear), but these relationships were unconfirmed because of difficulties with maintaining this fish species in captivity. We confirmed the suitability of Skipjack Herring as host for both mussel species, and we also showed that Alabama Shad (Alosa alabamae) is an additional suitable host for E. crassidens; both fish species produced large numbers of juvenile mussels. No other fish species tested (n=12) were suitable hosts for either mussel species. Our results, combined with results from other studies, suggest these mussel species are specialists on genus Alosa. Traditional methods for host identification were problematic for herrings because of their sensitivity to handling and the large volumes of water required to maintain them in captivity. In addition to traditional methods, we confirmed the suitability of these fishes as hosts using a novel technique in which fish gills infected with glochidia were excised from sacrificed fishes and held in recirculating holding tanks with flow until metamorphosis was complete. Completion of metamorphosis on excised gills required glochidia spend at least 11–17 d encapsulated on live fishes before gill excision. This technique may be useful for other large or sensitive fishes that do not lend themselves well to traditional methods for host identification. Confirmation of Alosa spp. as primary hosts for R. ebenus and E. crassidens supports the idea that dams and other river modifications that disrupt migrations of these fishes are key factors in the range restrictions of these mussel species.