First examination of diet items consumed by wild-caught black carp (Mylopharyngodon piceus) in the U.S.

Black carp (Mylopharyngodon piceus) were imported to the U.S. in the 1970s to control snails in aquaculture ponds and have since escaped from captivity. The increase in captures of wild fish has raised concerns of risk to native and imperiled unionid mussels given previous literature classified this species a molluscivore. We acquired black carp from commercial fishers and biologists, and examined digestive contents of 109 fish captured over 8 y from lentic and lotic habitats in the central and southern U.S.A. Digestive tract contents were preserved, and diet items inventoried. We identified 59 aquatic animal taxa (21 mollusks, 27 insects, and 11 other invertebrates) and various plant material including nuts and seeds; no fish were found. Approximately 45% of stomachs examined were empty or only contained flukes (Trematoda) that had infected mollusks before they were ingested. Nonempty stomachs contained snails (16.5%), bivalve mussels (22.8%), and insect larvae (net-spinning caddisflies, 15.6%; burrowing mayflies, 6.4%; and midges, 13.7%). Fish also consumed freshwater sponges (Porifera), moss animals (Bryozoa), crustaceans (Ostracoda and Decapoda), water mites (Acarina), and three worm phyla (Nematoda, Nemertea, Annelida). Seven taxa of unionid mussels were identified from shell fragments among the fish we examined, all of which are found in habitats with soft mud or sand/silt substrates. Diet of fish captured in lentic environments contained significantly higher richness than those captured in lotic environments. Individual black carp often contained large numbers of only one or two diet items that were assumed locally abundant and did not always crush the shells of mollusks. Most fish we examined consumed benthic prey, which supports the classification of black carp as a benthic foraging species. However, the presence of other aquatic taxa associated with pelagic or subsurface zones suggests black carp are opportunistic in their consumption of diet items and flexible in their feeding modes.