Freshwater Drum Dietary Niche and Specialization in the Wabash River

We explored diet of freshwater drum (Aplodinotus grunniens) throughout the Wabash River, USA. Freshwater drum (FWD) are one of the most abundant taxa within the Mississippi River basin, however, they are largely understudied. Our study objective was to describe the diet of FWD and test for covariation with availability, size, and gender. FWD were collected throughout the Wabash River and measured, weighed, and assessed for gender. FWD stomachs (n=300) were dissected and contents were compared to potential prey availability (inferred through standard river invertebrate surveys), spatial position along the river continuum, size, and gender. We used detrended correspondence analysis to describe diet and indicator species analysis, multi response permutation procedure, and Pianka’s degree of niche overlap to assess and describe differences. FWD diets significantly differed from prey availability. We identified consistent prey utilization despite river distance, a trend not reflected in the overall invertebrate community samples. FWD diets varied with size and gender. Caddisfly (hydropsychidae) taxa were the predominant food items in small and medium fish (<500mm) while larger fish (>550mm) tended towards molluscan and crayfish prey items. We suggest that FWD are a trophic specialist and that their distribution in large river systems is linked to microhabitat supporting their prey base.