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 that to raise the culture density of rotifers to 10(4) ind. ml(-1), inhibitory factors (low dissolved oxygen, foaming separation, and NH3-N toxicity) needed to be reduced through oxygen gas supplementation and regulation 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 harvest. Another problem is the development of a more accurate quantitative method for determining Chlorella and rotifer densities that could replace the conventional counting method. These problems have been resolved in the following manner. (1) Filtering equipment for removing particulate 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 density culture at 10(4) rotifers ml(-1) was possible without clogging of the collection net. (2) Quantitative determination of rotifers by a centrifugation method: We determined the abundance of rotifers by centrifuging samples and measuring their packed volume (PV, mi l(-1)). PV of rotifers was easier to and more accurate to measure (coefficient of variation, 4%) than a direct count of the density (coefficient of variation, 15%). Organic wastes in rotifer cultures made the measurement of rotifer PV difficult. By placing a filter in the mass culture tank, however, the boundary between rotifers and other organic wastes in a centrifuge tube was easily visualized.