Feeding Ecology of Invasive Three-Spined Stickleback (Gasterosteus aculeatus) in Relation to Native Juvenile Eurasian Perch (Perca fluviatilis) in the Pelagic Zone of Upper Lake Constance

The fish community of Lake Constance, a large, deep, oligotrophic lake has undergone drastic changes in recent years, with the sudden rise to dominance invasive three-spined stickleback ( Gasterosteus aculeatus ) pelagic zone, rather atypical habitat for this species Central Europe. core objective study was compare feeding ecology and young Eurasian perch Perca fluviatilis unique situation identify reasons unexpected dominance, possible food niche time overlap, discuss consequences reshaped community. diel patterns prey compositions sticklebacks juvenile (0+) sampled October 2018 March 2019 were studied analyzing stomach contents. diets both mostly comprised zooplankton, copepods appearing greatest numbers. Benthic airborne insects consumed occasionally, by sticklebacks. Both exhibited peaks activity early morning, afternoon dusk, species, stomachs fullest at dusk. Stickleback contained about 20% more night than perch, mean estimated nocturnal fullness values almost 50% greater. Night confirmed digestive states, pointing competitive advantage over perch. Dietary composition varied 24-h cycle pattern consumption different between species. Perch comparatively small cladocerans Bosmina spp.), while larger Daphnia appeared often stomachs. In seasonal variation diet mirrored availability, indicating some degree opportunism. A Morisita-Horn index value 0.95 dietary overlap suggesting large population may exert effect on when resources are limited. longer periods greater intake nutritive high quality like daphnids can contribute rapid success dominating zone Constance.