Egg-feeding in the freshwater piscicolid leech Cystobranchus virginicus (Annelida, Hirudinea)

Abstract. Leeches are common terrestrial and aquatic annelids, parasitizing or feeding on a wide range of host taxa. Here we report evidence for an unusual feeding behavior of egg‐feeding in the piscicolid leech Cystobranchus virginicus. We identified distended specimens of C. virginicus in the nests of at least 4 different fish species: Campostoma anomalum, Moxostoma carinatum, Moxostoma sp. (either M. anisurum and/or M. breviceps), and Nocomis leptocephalus. We collected a total of 41 leeches from the nests of these host species and documented at least 1 leech in 19 of 55 nests (35%), with many sites containing multiple leeches. Individuals of C. virginicus were not identified feeding on any of the 41 adult specimens of Moxostoma spp. or the 635 adult specimens of Nocomis leptocephalus examined, and were never found in the absence of active host spawning (26 sites). These results are consistent with individuals of C. virginicus being an opportunistic or possibly even an obligate egg‐feeder, potentially timing their own reproductive activities with the spawning of their fish hosts. The current distribution of C. virginicus has been expanded to include North Carolina, South Carolina, and Tennessee. The potential for leech species to induce mortality in developing fish eggs could be a concern for fish conservation and merits further investigation.