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Mass production of the resting eggs of the marine rotifers Brachionus plicatilis (formerly called L-type) and B. rotundiformis (called S-type) were achieved using a batch culture method [reviewed by Hagiwara, A., 1994. Practical use of rotifer cysts. The Israeli Journal of Aquaculture — Bamidgeh 46, 13–21]. This paper summarizes the further advancements achieved over the last three years. The efficiency of resting egg production can be improved by employing semi-continuous culture method. Some semi-continuous cultures collapsed between the 15–20th days due to bacterial effects. However, the rotifer culture was stabilized by placing filtration mats to remove organic material. Thus harvests of 8.1 × 10 2 resting eggs/day/g (dry weight) Nannochloropsis oculata were achieved, which is 3.0 times more efficient than that from batch cultures. Resting eggs of B. rotundiformis , however, were not mass produced after the exchange of culture water. Resting eggs can be stored in sea water for more than 20 years at 5 °C under complete darkness. Hatch rates of the eggs, however, decreased when stored with abundant organic matter. Resting eggs could be canned under an atmospheric pressure of 48–61 kPa after lyophilization (− 30 °C) without reducing their hatch rates.

The dietary value of dried, commercial Chlorella was compared with that of living marine Chlorella, and yeast, in relation to growth of the rotifer Brachionus plicatilis raised individually and by batch culture methods. A concentration of 50 μg/ml of dried Chlorella powder is near an optimal density for rotifer growth. The dried material in suspension is less effective for growth than living marine Chlorella, although it is much more effective than a suspension of yeast at the same density (50 μg/ml). In batch culture (12-l glass vessel), the rotifers grew from an initial inoculation of 13.2 individuals/ml to a density of 434 individuals/ml by the 16th day. About 107 rotifers could be removed from one batch culture in five harvests in the 41-day experimental period. The results indicate that dried Chlorella powder is an effective food for the rotifer Brachionus plicatilis.

This paper describes the chemical changes in culture water in closed culture systems with sand filter. Stabilization of inorganic nitrogen after sequential changes of ammonium-N and nitrite-N in a culture system with new filters takes from 40 to 60 days. The characteristic changes in chemical composition of aged culture water, namely an accumulation of nitrate and phosphate and lowering of pH and alkalinity, are discussed. The carrying capacity in a closed culture system is determined by using oxygen consumption during filtration as an index to indicate the degree of purification by filtration.