Co-occurring bighead and silver carps show similar food preference but different isotopic niche overlap in different lakes

Abstract

Silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis) are among the most important fish species in aquaculture and have been introduced to many countries. The feeding ecology of these filter-feeding cyprinids is not well understood and has been mostly based on gut content analyses. We analyzed δ13C and δ15N stable isotope ratios of food resources and fish muscle tissues in four Chinese lakes, where these two species co-occur. Data analysis through Bayesian mixing models revealed that both fish species had similar diets within lakes, and where dietary shifts occurred, both species displayed dietary shifts simultaneously. Diet was generally based on plankton, however, detritus was the main food in eutrophic lake subjected to urban pollution, likely due to resource availability. Niche overlap and width were also variable but in general clear size-based resource partitioning was observed, with bighead carp preying more on zooplankton and occupying a higher trophic position and silver carp feeding more on phytoplankton. Food particles smaller than 64 μm, had little importance in their diets.