Dietary overlap of invasive cyprinids and common carp in fishponds of Central Europe

Freshwater fishponds are an important part of the global aquaculture fish production, but they also are a source of invasive species with potentially negative impacts on pond ecosystems. In this study, we investigated dietary competition between common carp (Cyprinus carpio) and two invasive cyprinids, Pseudorasbora parva and Carassius gibelio, in fishponds of Central Europe. Using δ13C and δ15N stable isotopes analysis, we evaluated the extent of isotopic niche overlaps and the utilization of dietary sources by these species in fishponds that differ in the intensity of fish production. The isotopic niche of C. carpio and the invasive cyprinids overlap more in ponds with intensive (south-eastern Czechia) and semi-intensive (northern Austria) fish production then in ponds with low intensity production (eastern Slovakia). Our results also suggest that both invasive species opportunistically adjust their diet to their gape size and that they predominantly assimilate dietary energy from zooplankton and macroinvertebrates rather than from primary producers and detritus. Our study highlights the high potential of these invasive cyprinids to compete with C. carpio in fishponds of Central Europe. •Study of dietary overlap between common carp and invasive cyprinids in fishponds.•Isotopic niche overlap is higher in intensive and semi-intensive fishponds.•Low production intensity ponds show less dietary competition and niche overlap.•Invasive cyprinids in fishponds mainly consume zooplankton and macroinvertebrates.•Invasive cyprinids can have negative impacts on fishpond ecosystem and production.