Synergy between silver carp egestion and benthic fishes

Abstract

Many studies have shown that negative interactions exist between the invasive silver carp Hypophthalmichthys molitrix and the associated native fish community. The primary negative effect relates to the filter feeding capacity of Asian carp and thus dietary overlap and decreased fitness of native planktivorous fishes. However, from a nutrient transfer perspective, an alternative feedback loop may exist between invasive Asian carps and native fishes. We postulate that silver carp consuming small planktonic particles with low assimilation efficiency can subsequently egest larger, nutrient rich fecal pellets consumable by other fauna, which may have otherwise been unavailable. To evaluate this feedback loop, we extracted fecal pellets from the hindgut of silver carp. Fecal pellets were fed to age-0 channel catfish Ictalurus punctatus and blue catfish Ictalurus furcatus (i.e., < 130 mm) in a controlled laboratory setting. Both species of catfish consumed the fecal pellets and subsequently survived and increased in body mass (i.e., weight) over the 20-day trial period. These results suggest that a potential alternative feedback loop may exist between silver carp and members of the benthic community and therefore provide a pathway by which nutrients are translocated between habitats (i.e., pelagia to benthos). We suggest that undigested plankton consumed by silver carp can be converted into nutrient packed pellets and may provide an additional food source to benthic organisms such as age-0 channel catfish and age-0 blue catfish.