Laboratory feeding trials were conducted to determine how light intensity affects foraging success by the visual piscivore, the largemouth bass (Micropterus salmoides). Foraging success was greater than 95% at light levels ranging from low intensity daylight (2·43 10 2 lx) to moonlight (3 10 3 lx), but declined significantly to 62% at starlight (2 10 4 lx) and near 0% in total darkness. Over a range of low to high water clarities (0·5, 2·0, and 4·0 m Secchi depth), estimated depth limits for feeding during the day ranged between 5·5 to 44 m and from 1·6 to 13 m at night during a full moon. At starlight, light intensity rapidly attenuated to a level below the feeding threshold within 0·5 m of the surface at all water clarities. The depth of the water column available for feeding in low clarity water (0·5 m Secchi) was 67 and 75% less than at moderate (2·0 m Secchi) and high (4·0 m Secchi) water clarities. The findings illustrate how differences in the light environment can have important ramifications for predator-prey interactions.

Previous workers inferred from stomach analyses that threadfin shad (Dorosomapetenense) ate plankton by both filter and particulate feeding. These inferences were confirmed in this study by laboratory experiments in which both types of feeding were observed. Threadfin shad consumed relatively small food particles ( < 0.39 mm) by filtration, while larger prey (7.5 mm) were eaten individually. The shad were able to filter feed on small foods (brine shrimp nauplii and phytoplankton) at all light intensities from 0 to 9 x 10' fL. These data indicate that under natural conditions shad can filter feed at any time of the 24 h period if food conditions are sufficient to trigger feeding. Filter feeding is probably induced by chemoreception rather than vision. The particulate feeding rate decreased as light intensity decreased, reaching a minimum between 9 x lo-' and 9 x fL. From these data it is inferred that particulate feeding is a visual process in this species, requiring intensities equivalent to bright moonlight or greater. Filter and particulate feeding abilities allow threadfin shad to consume most of the different types of plankton and to change their diet with seasonal changes in the composition of the plankton.

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