In two mesocosm experiments of cross-classified design, using sixteen
900-liter containers, we measured how benthivorous, omnivorous, and pl
anktivorous fish interact with the sediment-water interface to influen
ce planktonic and benthic production. Experiment 1 used three fish tre
atments (Ictalurus punctatus, Notemigonus crysoleucas, Lepomis macroch
irus) and a fishless control in the presence or absence of a natural p
ond sediment layer. The benthivorous Ictalurus enhanced turbidity but
had no effects on dissolved oxygen, diel changes in dissolved oxygen,
pH, or nutrient concentrations. All parameters measured were unaffecte
d by the planktivorous Notemigonus. Experiment 2 compared Ictalurus ne
bulosus with those of other benthivorous (Cyprinus carpio) and omnivor
ous (Dorosoma cepedianum) fish, again in the presence or absence of a
sediment layer but at a higher stocking density than experiment 1. In
the second experiment, Dorosoma enhanced dissolved oxygen levels but h
ad no effect on turbidity while Cyprinus and Ictalurus enhanced turbid
ity but suppressed dissolved oxygen. Nitrogen concentrations in sedime
nt tubs were enhanced by Cyprinus and Ictalurus but nitrogen concentra
tions in sediment-free tubs were enhanced by Dorosoma. This would sugg
est that the benthivores affected nutrient levels through resuspension
of sediments while omnivores affected nutrient levels through physiol
ogical processes.