High density culture of the freshwater rotifer,Brachionus calyciflorus

The freshwater rotifer, Brachionus calyciflorus is one of the live food organisms used for the mass production of larval fish. In this study possibility of obtaining high density cultures of the freshwater rotifer B. calyciflorus were investigated. The two culture systems used differed in their air and dissolved oxygen supplies using three temperatures in each case: 24, 28 and 32 °C. Rotifers were batch-cultured using 5 l-vessels and fed with the freshwater Chlorella. The growth rate of rotifers significantly increased with an increase in temperature. The maximum density of the rotifers with air-supply at 24 °C, 6500 ind. ml^–1, was significantly lower than those cultured at 28 and 32 °C, i.e. 8600 and 8100 ind. ml^–1, respectively. Dissolved oxygen levels decreased with time and ranged from 0.8 to 1.4 mg l^–1 when the density of freshwater rotifer was the highest at each temperature. The highest density (19200 ind. ml^–1) of freshwater rotifer was obtained in cultures with a supply of oxygen at 28 °C. Densities of 13500 and 17200 ind. ml^–1 were found at 24 and 32 °C, respectively. Levels of NH₃-N increased with time and a dramatic increase of NH₃-N was observed at high temperatures. Levels of NH₃-N at 24, 28 and 32 °C were 13.2, 18.5 and 24.5 mg l^–1, respectively. These levels coincided with the highest rotifer density at each of the three temperatures. When rotifers were cultured with an oxygen-supply and pH was adjusted to 7, the maximum density of rotifer reached 33500 ind. ml^–1 at 32 °C . These results suggested that high density culture of freshwater rotifer, B. calyciflorus could be achieved under optimal conditions with DO value of exceeding 5 mg l^–1 and NH₃-N values of lower than 12.0 mg l^–1.