Immobilized microalga Scenedesmus quadricauda (Chlorophyta, Chlorococcales) for long-term storage and for application for water quality control in fish culture

The green microalga Scenedesmus quadricauda was cultivated and entrapped into alginate-beads for long-term storage. The entrapped algal cells were alive and maintained their physiological activities after 3 years of storage in absolute darkness, at 4 degreesC without culture medium. The number of coenobia in the beads increased more than ca. 40 times after they were re-cultured in an aqueous medium for 4 weeks. TEM observations showed that the organelle pyrenoids of entrapped S. quadricauda cells disappeared after long-term storage. However, the pyrenoids were reconstructed when the algal cells were re-cultured into an aqueous medium with light. These results indicated that the entrapped algal cells remained alive by consuming the reserve caps of pyrenoids. The algal beads were applied to water quality control in fish (tilapia) culture. In those cultures with algal beads, the ammonium concentrations decreased markedly. Immobilized microalga in alginate-beads, particularly the species S. quadricauda, can be used as algal stock for long-term algal species preservation in the laboratory and subsequently can be used for controlling the water quality in tilapia cultures. (C) 2001 Elsevier Science B.V. All rights reserved.