Development of Ultra-High-Density Culture System for Mass Production of a Zooplankton Rotifer as Larval Fish Food by Controlling the Dissolved Oxygen Concentration : Monograph, Seibutsu-kogaku, 81, 112-117, 2003
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概要
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In recent years, the production of larval fish has been rapidly increasing worldwide. A zooplankton, the rotifer Brachiorms 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 individuals (ind.)/ml, which meant large culture tanks of over hundred 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_<&dwanglw;>α were rather inhibitory to rotifer growth. Hence, the feeding of O_2 gas was essential to avoid oxygen deficiency. Third, we found that main taining 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 high-density 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 l/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 100 l capacity.
- 2003-04-25
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