The microalgae Tetraselmis suecica, Nannochloropsis oculata, Chlorella sp., Isochrysis galbana, and Dunaliella tertiolecta were used as food for the rotifer Brachionus plicatilis (L type) raised in laboratory conditions at 25 +/- 1 degrees C and 25%. salinity. Filtration and ingestion rates of the rotifer were determined to study the effects of different microalgae densities and feeding times on the feeding behavior of the starved B. plicatilis. The highest filtration (11.5 x 10(-4) ml/ind/min) and ingestion (246.99 x 10(2) cells/ind/min) rates were obtained with N. oculata. The filtration rates dropped when the microalgae density rose beyond the optimum level, but ingestion rates varied with algae species. Feeding time significantly influenced these rates: after 60 min, both rates dropped.