The performance of a high-density continuous system was evaluated as an alternative to conventional low-density batch-culture systems for culturing the rotifer Brachionus plicatilis. Rotifer densities ranging from 1700 to 3760 individuals/mL were achieved in 4 different trials that lasted 10-18 days. Problems associated with NH(3)-N and pH were controlled by increasing the water exchange rate and periodic addition of ammonia remover. While NH(3)-N and pH values were 0-8.8 mg/L and 6.9-9.3, respectively, the most important problem was the accumulation of TSS at concentrations of up to 85 mL/L within a very short time after start-up. Further studies are required to develop simple and cost-effective filters that reduce TSS concentrations. Use of continuous systems in combination with concentrated algae is potentially an effective alternative to existing batch-culture systems.