Feeding strategy displayed using the Amundsen et al. (1996) modification of the Costello (1990) graphical method for A European perch B racer goby C monkey goby, in the Bug River (only main food categories included and data from sites pooled for species) D explanatory diagram (%Nps – prey specific abundance; %F – frequency of occurrence defined as percentage of fish guts containing given prey category in relation to the total number of fish with guts containing any food).