Development of a continuous culture system for stable mass production of the marine rotifer Brachionus

In order to improve culture stability, as well as to reduce labor and space for mass production of the marine rotifer Brachionus, an automatic continuous culture system has been developed for practical use. The system consists of a filtration unit, a culture unit and a harvest unit. In this system, filtered water and food are continuously supplied into a rotifer culture tank at a pre-determined rate, and the same amount of culture water is transferred into a harvest tank to obtain rotifers at a significant biomass. B. rotundiformis (so-called S-type) and B. plicatilis (so-called L-type) were successfully mass-produced from the system, under regulated conditions of 30 degrees C (for S-type) or 24 degrees C (for L-type), 20 ppt diluted sea water and total darkness. As food for rotifers, commercially available concentrated fresh water Chlorella vulgaris was used. The dilution rate was adjusted to 0.6-0.7 d(-1) for S-type rotifer and 0.25 d(-1) for L-type rotifer, respectively. The average production was about 2.1 billion rotifers d(-1) from a 1-m(3) S-type continuous culture in which high rotifer densities ranging from 3000 to 6000 ind. ml(-1) were maintained. On the other hand, about 0.17 billion rotifers d(-1) on average were obtained from a 500-liter L-type culture, with densities ranging from 1100 to 2200 ind. ml(-1). The longest duration for a continuous culture was over 110 days. Furthermore, experiments utilizing five enrichment techniques indicate that rotifers from the continuous culture system can easily be nutritionally enriched in the same manner as those from common batch culture systems.