In the cultivation of microalgae, it is first necessary to have algae strains.  The algae strains can be purchased from the relevant security agencies, and can also be separated from natural waters. From the mixed biota of natural waters, a certain method is used to separate the required individuals and obtain a single culture. At present, there are not many algae species that can successfully produce large quantities in China, and they are far from meeting the needs of artificial breeding of various economic animals. This requires the isolation and cultivation of new species of algae. On the other hand, if the algae species are contaminated by predator organisms and other hetero- algae, they must also be purified by separation.