Use of Native and Nonnative Fish Hosts by the Freshwater Mussel Anodonta californiensis (California Floater) in the Columbia River Basin

ABSTRACT Populations of many native freshwater mussels such as the California floater, Anodonta californiensis, are declining in the Columbia River Basin in the western United States. There are many possible reasons for this decline, including increased presence of nonnative fishes, especially piscivores that displace and reduce the abundance of native fishes. These nonnative fishes can negatively influence the early life history of A. californiensis, because this mussel uses native fishes to complete its life cycle. While Anodonta spp. can use nonnative fishes as hosts with limited success, the extent of this for A. californiensis is not well understood. We determined if the glochidia (larvae) of A. californiensis can successfully metamorphose using certain nonnative fishes, and we quantified differences in host effectiveness (number of juveniles produced) between native and nonnative fishes based on available fin area for attachment. Overall, native fishes hosted an average of 107.4 ± 39.9 (mean ± SE) juvenile mussels per fish while nonnative fishes hosted an average of 5.5 ± 4.9 juveniles per fish. This conclusion was unchanged when standardized for fish attachment area. Encystment of glochidia on native fishes yielded an average of 1.0 ± 0.1 juveniles/mm2 of attachable surface (total area of fins) area while nonnative fishes yielded an average of 0.16 ± 0.1 juveniles/mm2. The nonnative channel catfish, Ictalurus punctatus, did not yield any juvenile mussels and was identified as a nonhost species for A. californiensis. All other nonnative fishes tested were determined to be poor or marginal hosts. All native fishes were determined to be primary or secondary hosts for A. californiensis. The native fishes that yielded the highest number of juvenile mussels were sculpins, Cottus spp., and the redside shiner, Richardsonius balteatus, with an average of 196 and 151 juveniles per individual of each species, respectively. Our findings show that nonnative fishes are poor hosts for A. californiensis. However, nonnative fishes may contribute to the decline of native mussels in the Columbia River Basin by directly preying on and reducing the abundance of native host fishes and mussels. Future conservation plans for A. californiensis should consider the potential negative influence of nonnative fishes.