MICRO-ALGAE AS A SOURCE OF NUTRIENTS FOR DAPHNIDS

Abstract

The experimental data presented above show clearly that the unicellular algae such as Chlorella, Scenedesmus and Chlamydomonas, are excellent feed for daphnids. Although less effective than these algae, filamentous blue-green algae Tolypothrix and Nostoc, also serve as nutrient for daphnids. For the past several years we have been conducting experiments of seeding Tolypothrix and other nitrogen-fixing blue green algae on the paddy-field in order to test the possibility of increasing rice crop by virtue of their nitrogen-fixing capacity(9). One of the serious problems arising in these field-experiments was that, occasionally, the seeded algae dissappeared 1955 Micro-algae as a Source of Nutrients for Daphnids 141 completely from the field within 1 or 2 weeks In such cases we found, almost without exception, that the field water became abundant first with unicellular algae such as Chlorella and Scenedesnzus, and then with water- fleas which eventually ate up the seeded blue-green algae. We learn from the above experiments that in order to assure the growth of nitrogen-fixing blue-green algae in the paddy-field, some measure must be taken to prevent the growth of water-fleas or to suppress the growth of unicellular green algae which remarkably favors the increase of the population of daphnids.