Feeding ecology of invasive Perccottus glenii (Perciformes, Odontobutidae) in Slovakia

Stomach contents of 331 specimens of Perccottus glenii (Perciformes: Odontobutidae) were analysed. Chironomids and ephemeropterans dominated the diet of all size classes of fish; however, the frequency of crustaceans was also high. Micro-crustaceans (ostracods, copepods and cladocerans) dominated in lower size classes (20-39 mm); macro-crustaceans (Isopoda, Amphipoda) dominated in higher size classes (up to 79 mm). The proportion of crustaceans decreased from the size class 80-89 mm. With the increasing size of fish the frequency of molluscs (Gastropoda) increased, the maximum was in size class 70-79 mm. Cannibalism occurred from 60 mm, and it was significant from 80 mm. The highly mobile invertebrates (Coleoptera, Heteroptera) were found in the largest size classes. In middle size classes (40-59 mm), the widest spectrum of prey units was documented; the food variability of small (90 mm) individuals was poor. Differences in the diet composition of small individuals were negligible; the diet of the largest ones differed significantly. According to diet, two feeding size class groups were recognised: the first