EFFECT OF FOOD TYPE AND CONCENTRATION ON THE SURVIVAL, LONGEVITY, AND REPRODUCTION OF DAPHNIA-MAGNA

The freshwater microalgae Ankistrodesmus falcatus and Scenedesmus incrassatulus, at three concentrations (6, 12 and 18 mg l-1, dry weight), were tested as diets for Daphnia magna cultured in reconstituted hard water, at 19 +/- 1-degrees-C. Effects on survival, and reproductive characteristics were evaluated during a complete life-cycle. Test animals fed with the highest food concentration had the lowest survival, longevity, number of clutches, and average inter-brood times, but the total offspring was similar to that obtained with the lowest food concentration, for the same species of alga. Average longevity ranged from 40 to 85 days, with a minimum of 24 and a maximum of 119 days. The average inter-brood time ranged from 4.2 to 5.8 days, the highest values being observed at the lowest food concentration. The average total offspring was maximum for the intermediate concentrations of both algae. The maximum number of clutches ranged from 9 to 23, with the lowest values being observed at the highest food concentration. Even though both microalgae had similar effects on survival and reproduction, and the greatest differences observed were related to food concentration, it seems that S. incrassatulus is a comparatively better food for D. magna. The most suitable food level should be determined prior to carrying out chronic bioassays, and it is also an important factor in cultures for obtaining neonates for toxicological tests.