LAUSR

Large, predatory, non‐indigenous species such as the cladoceran, Bythotrephes longimanus, can have a profound effect on aquatic food webs, but determining the prey consumed by such species is problematic because they shred prey externally and consume only soft body tissues. We assessed the usefulness of an immunochemical approach, in which putative zooplankton prey were homogenized and polyclonal antibodies against total proteins were raised in rabbits and purified against predator proteins. Using either dot‐blot or enzyme‐linked immunosorbent assay‐plate formats, assays easily detected prey proteins in single B. longimanus. Issues encountered included some degree of cross‐reaction with predator proteins and among prey species for some antisera and questions concerning determination of a correct blank value for assays, however, there are feasible approaches to resolving these issues. Immunochemical assays were readily applied in to a total of 185 individual B. longimanus in the Lake Michigan pelagic ecosystem in summer of 2008 and 2009 and indicated ingestion of cladoceran and copepod species, typically described in the literature, but also dreissenid veliger larvae and the large copepod Limnocalanus macrurus, not usually considered prey for Bythotrephes. Assays results showed some degree of correlation with numerical abundances of zooplankton prey in the water column, suggesting generalist feeding. Protein immunochemical assays offer a quick, sensitive and practical approach to examining planktonic food‐web questions that are compatible with, but have certain advantages over, alternatives such as nucleic acid techniques.