Food of introduced pumpkinseed sunfish: ontogenetic diet shift and seasonal variation

The pumpkinseed sunfish Lepomis gibbosus introduced into Lake Banyoles (Spa in) were predominantly littoral but there was a tendency of large fish to u se deeper zones. Their diet was dominated by littoral macrobenthos, particu larly amphipods (Echinogammarus sp.). There was ontogenetic variation in th e diet, with small young-of-the-year (L-F<4 cm) feeding on several littoral microcrustaceans, especially the cladoceran Ceriodaphnia reticulata, where as larger fish shifted to a freshwater shrimp (Atyaephyra desmaresti), snai ls and damselfly larvae. Seasonal variation in diet was linked to resource availability, with consumption of fish eggs and plant debris in spring and summer. In autumn, pumpkinseeds were partially zooplanktivores, preying on the cladoceran Daphnia longispinn. The diet of pumpkinseeds in Lake Banyole s and other Iberian populations shows less molluscivory than North American populations. The potential ecological impact of this successful exotic spe cies involves mainly predation on fish eggs and molluscs. (C) 2000 The Fish eries Society of the British Isles.