Daphnia, diet

In 1957, Schwartz and associates showed that the toxic element selenium was also a nutritional factor essential for prevention of the death of liver cells in rats.527 Liver necrosis would be prevented by as little as 0.1 ppm of selenium in the diet. Similar amounts of selenium were shown to prevent a muscular dystrophy called "white muscle disease" in cattle and sheep grazing on selenium-deficient soil. Sodium selenite and other inorganic selenium compounds were more effective than organic compounds in which Se had replaced sulfur. Keshan disease, an often fatal heart condition that is prevalent among childen in Se-deficient regions of China, can be prevented by supplementation of the diet with NaSe03.528 Even the little crustacean "water flea" Daphnia needs 0.1 part per billion of Se in its water.529... 

Although Cyclops is the most widespread copepod in lakes of this region (78), its diet is incompletely understood. Cyclops had the highest 15N content of all zooplankton, and in the fertilized side of the lake Cyclops was nearly one full trophic level enriched ( 3%>) above Daphnia. Thus Cyclops may function as an omnivore or a carnivore in this lake, and a second experiment was performed to address this question. Overall, these natural-abundance isotopic values are similar to the 815N values reported for zooplankton in other arctic lakes (49, 52). 

Daphnia is commonly maintained in laboratories for assaying toxic substances in water. Water fleas are often of great importance in the diets of fishes, especially young fishes, and predaceous insects, such as many of the Diptera larvae. 

V. Partali, Y. Olsen, P. Foss, S. Liaaen-Jensen (1985). Carotenoids in food chain studies -1. Zooplankton Daphnia magna) response to a unialgal (Scenedesmus acutus) carotenoid diet, to spinach, and to yeast diets supplemented with individual carotenoids. Comp. Biochem. Physiol., 82B, 761-112. 

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