Resource use of crucian carp along a lake productivity gradient is related to body size, predation risk, and resource competition

Generalist fish species can feed on a wide resource spectrum and across trophic levels depending availability interactions. Crucian carp (Carassius carassius) represents good candidate to investigate variation in the ecology of generalist as it be found highly variable communities its use is well documented. In this study, we explored crucian at individual population using stable isotope gut content analysis. We tested if varied according lake productivity, predation risk, intra- interspecific competition, or size. that preference was among within lakes. predator-free lakes, small occurred high densities, showed increased interindividual specialisation, relied mainly pelagic zooplankton. presence predators, large low densities included greater proportions benthic macroinvertebrates their diet. This shift further favoured productive, shallow lakes where littoral prey were probably abundant. Resource partitioning an important factor determining niche use, had higher position absence other cyprinids. dynamic food preferences response environmental conditions. Overlooking complex diet may lead oversimplification freshwater community dynamics.