Tanks of 0.5 to 3 ton capacities are used in the changing-tank method. At the onset, one tank (tank A) is inoculated with Chlorella. After the Chlorella densities reach 1 x 10⁷cells per milliliter, B. plicatilis is inoculated at a density of 10 to 20 individuals per milliliter. When green water is used and becomes clear, bread yeast is given twice daily at a ratio of 1g of yeast to 10⁶ rotifers. When the density of B. plicatilis exceeds 100 individuals per milliliter (about 5 to 7 d after inoculation), much of the culture is harvested to feed the larvae. A small volume is retained to serve as inocula for another Chlorella tank (tank B). Thus, the process is transferred from tank A to tank B, B to C, C to D, etc. As described, the repetition of the procedure, commencing with the culture of Chlorella, followed by inoculation with rotifers, and then the harvest, is called the method of changing tanks. The individual capacity and the number of tanks used depend on the quantities of rotifers needed. This method is simple and reliable. It usually does not require much space, but is more labor intensive (I-Chiu et al., 1993).