Two experiments (Exp. I: batch method using 1l vessels and Exp. II: semi-continuous method using 200l tanks) were carried out in order to investigate the effect of acidification of the media in high density cultures of the rotifer Brachionus rotundiformis on the reduction of poisonous undissociated ammonia.
Rotifer were cultured in media with pH adjusted to 6, 7 and 8, and without pH adjustment, bubbling oxygen gas and feeding commercial condensed Chlorella regularis. The pH was adjusted with the automatic addition of HCl (35%) and NaOH (10 N) through a pH controller.
The concentration of undissociated ammonia in the medium without pH adjustment (Exp. I) and of 8 pH (Exp. II) increased to 27 and 16 ppm, and the growths of rotifer population were inactive and their maximum densities were 8, 000 and 3, 000 individ./ml, respectively. On the other hand, the concentration of undissociated ammonia in the medium of 7 pH remained less than 10 ppm, and in the medium of 6 pH, it was only 2 ppm. The growths of rotifer population in their media were remarkably active, and their maximum densities reached 22, 000 to 34, 000 individ./ml (Exp. I) and 9, 000 to 13, 000 ìndivid./ml (Exp. II).
