溶存酸素濃度制御による栽培漁業用餌料ワムシの超高密度培養法の開発と実用化

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In recent years, the production of larval fish has been rapidly increasing worldwide. A zooplankton, the rotifer Brachionus rotundiformis, plays a very important role as the food of many marine larval fishes used in mariculture and fish cultivation. A typical mariculture corporation requires about 10 billion rotifers every day. However, the culture density of rotifers in the conventional culture method was only ca, 200 individnals (ind.)/ml, which meant large culture tanks of over handred tons capacity were essential for the production of enough rotifers. Hence, we developed a high-density culture method incorporating the ideas and techniques of microbial engineering. First, condensed freshwater Chlorella were employed as new food for rotifers instead of the bakery yeast and marine Chlorella used in the conventional culture method. Second, we demonstrated that mechanical agitation, a high aeration rate, and the use of a fine porous sparger to attain a high k_La were rather inhibitory to cotifer growth. Hence, the feeding of O_2 gas was essential to avoid oxygen deficiency. Third, we found that maintaining the pH at 7.0 by automatic addition of HCL to promote the dissociation of NH_3 to NH_4^+ and OH^- was very useful in reducing inhibition by NH_3. Fourth, a filtration unit was fitted in the culture tank to remove waste matter from the culture liquid. Using these techniques, the culture density of rotifer increased to 20,000 ind./ml. Our highdensity culture method is now being used by many mariculture corporations in Japan. Recently, we developed a novel culture system using a continuous membrane filtration unit (CMFU) for ultra-high -density culture. In this culture system, NH_4^+ and soluble organic substances, which can be nutrients for bacteria, are removed from the culture liquid. Using the CMFU, the rotifer density increased to 160,000 ind./ml and the population of Vibrio sp. inhabiting in the rotifer body decreased to 1/100,000 of that of a culture without CMFU. This new culture system is expected to have great potential for the mass production of sterile rotifer using a culture tank smaller than 100l capacity.
2003-03-25

溶存酸素濃度制御による栽培漁業用餌料ワムシの超高密度培養法の開発と実用化

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