In a high density culture of rotifer (beyond the levels of 103ind./ml), the amount of aeration needed to maintain an optimum dissolved oxygen (DO) level increases. In order to investigate the effect of aeration on the population growth of rotifer, a series of experiments were carried out. The S-type rotifer Brachionus rotundiformis was cultured at high density using 10l vessels under different aeration conditions. Air or oxygen gas was introduced into the culture media through two types of sparger which formed different sizes of bubbles, at aeration rates from 0.1 to 2.0vvm. The bubble-size from the two kinds of sparger were estimated from the value of KLa (volumetric oxygen transfer coefficient). When the aeration rate was high or the ceramic sparger that formed smaller bubbles was used, DO in the culture system remained at a high level. However, under these conditions, the growth of the rotifer population was seriously inhibited due to very high aeration rates and small bubbles, possibly as a result of foaming separation. When oxygen gas was introduced into the culture system, the density of rotifer was higher than that when air was introduced. Therefore, it is recommended to introduce high-purity oxygen gas for a high density culture to avoid any growth inhibition and to maintain optimum DO.
