Effects of crepuscular photoenvironment on light-induced behavior of Daphnia

Phototactic response rates in the aquatic crustacean Daphnia magna were found to increase greatly when cultured under a lighting regime that included simulation of sunset and sunrise. The changes in intensity and color of the crepuscular periods are known to be the primary stimulus for vertical migrations of many planktonic forms, and may have importance to many other animals as well. The value of this type of lighting to investigators of animal behavior and physiology is discussed.