The ingestion rates of filter-feeding gizzard shad for different sizes of suspended particles were measured using mixtures of microspheres and zooplankton. Ingestion rate increases as a function of particle size, leveling off at 60 pm. The particle-size-dependent ingestion rates were consistent with a model of filtering efficiency based on the cumulative frequency of interraker distances of gizzard shad gill rakers.Comparison of ponds containing gizzard shad with control ponds without fish showed that gizzard shad suppressed Ceratium, the only phytoplankton species large enough to be ingested at a maximum rate. Gizzard shad did not have a significant effect on populations of Synedra, Peridinium, Navicula, Kirchneriella, Cyclotella, and Chlamydomonas. Populations of Ankistrodesmus, Cryptomonas, Cosmarium, Rhodomonas, and algae and bacteria from 2-4 pm were enhanced by gizzard shad.

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In laboratory feeding trials, gizzard shad Dorosoma cepedianum of 5.3–17.5‐cm standard length fed on zooplankton as pump filter feeders, collecting prey by a series of rapid suctions not directed at individual prey. Buccal volume, determined from plaster casts, increases as a power function of fish standard length. Pumping rates decrease exponentially with length. A model of filtering rate, the product of buccal volume and pumping rate, was corroborated by feeding trials in which gizzard shad cleared zooplankton from a pool. By this model, absolute filtering rates increase as a power function of fish length while filtering rate per gram of fish decreases as a power function of length. Populations of gizzard shad can filter substantial volumes of lake water each hour.

We conducted an outdoor mesocosm experiment of factorial design consisting of three levels of nutrient supply (no nutrient addition and additions of nitrogen and phosphorus in ratios of 10 :1 and 45 : 1) cross-classified with two levels of bluegill (Lepomis macrochirus) (presence and absence) . Nutrient supply significantly affected total phosphorus (TP), total nitrogen (TN), TN : TP ratio, turbidity, Secchi depth, phytoplankton chlorophyll, filamentous blue-green algae, periphyton chlorophyll, Asplanchna and nonpredatory rotifers . The presence of bluegill significantly increased TP, turbidity, diatoms, unicellular green algae, colonial blue-green algae, filamentous blue-green algae, periphyton chlorophyll, Asplanchna and non-predatory rotifers, and decreased Secchi depth, cladocerans, cyclopoid copepodids, copepod nauplii and chironomid tube densities . Nutrient supply and fish effects were not independent of each other as shown by significant nutrient x fish interaction effects for TP, Secchi depth, filamentous blue-green algae, periphyton chlorophyll, Asplanchna and non-predatory rotifers .

We conducted an outdoor tank experiment of factorial design with three levels of phosphorus addition cross‐classified with two levels of mosquitofish (Gambusia affinis) at two lake sites, allowing us to examine both main effects and interaction effects of phosphorus, fish, and site on phytoplankton biomass and zooplankton. Phosphorus addition significantly increased total phosphorus concentration and chlorophyll and decreased Secchi depth. Fish significantly decreased cladoceran densities and Secchi depth and increased chlorophyll and turbidity. Most phosphorus and fish effects were independent of each other except for a significant phosphorus × fish interaction on rotifers. The two sites had significant differences in total phosphorus concentration, turbidity, Secchi depth, chlorophyll, and densities of cladocerans, copepods, and rotifers. The only significant site ×phosphorus interaction was for total phosphorus. Significant site x fish interactions were detected for turbidity, Secchi depth, chlorophyll, and densities of cladocerans and rotifers. Fish effects were independent of phosphorus addition but dependent on site‐specific plankton community composition.