RECENT DEVELOPMENT OF A HIGH-DENSITY MASS-CULTURE SYSTEM FOR THE ROTIFER BRACHIONUS-ROTUNDIFORMIS TSCHUGUNOFF

Feeding rotifer mass cultures condensed Chlorella made it possible to culture rotifers at 10(3) ind. ml(-1) Subsequently, it was realized th at to raise the culture density of rotifers to 10(4) ind. ml(-1), inhi bitory factors (low dissolved oxygen, foaming separation, and NH3-N to xicity) needed to be reduced through oxygen gas supplementation and re gulation of pH at 7. However, even after these improvements, problems remained to be solved. One is controlling debris, particulate organic matter and microbes which often clog the collection nets during harves t. Another problem is the development of a more accurate quantitative method for determining Chlorella and rotifer densities that could repl ace the conventional counting method. These problems have been resolve d in the following manner. (1) Filtering equipment for removing partic ulate debris in the culture media: Filtering equipment made of a nylon mat and a stainless steel frame was developed to increase the surface area for debris removal. Using this filter, the harvest of high densi ty culture at 10(4) rotifers ml(-1) was possible without clogging of t he collection net. (2) Quantitative determination of rotifers by a cen trifugation method: We determined the abundance of rotifers by centrif uging samples and measuring their packed volume (PV, mi l(-1)). PV of rotifers was easier to and more accurate to measure (coefficient of va riation, 4%) than a direct count of the density (coefficient of variat ion, 15%). Organic wastes in rotifer cultures made the measurement of rotifer PV difficult. By placing a filter in the mass culture tank, ho wever, the boundary between rotifers and other organic wastes in a cen trifuge tube was easily visualized.