A HIGH-DENSITY CULTIVATION OF ROTIFER IN AN ACIDIFIED MEDIUM FOR REDUCING UNDISSOCIATED AMMONIA

Two experiments (Exp. I: batch method using 1 l vessels and Exp. II: s emi-continuous method using 200 l tanks) were carried out in order to investigate the effect of acidification of the media in high density c ultures of the rotifer Brachionus rotundiformis on the reduction of po isonous 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 adju sted with the automatic addition of HCl (35%) and NaOH (10 N) through a pH controller. The concentration of undissociated ammonia in the med ium 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 mere 8,000 and 3,000 individ./ml, respectivel y. On the other hand, the concentration of undissociated ammonia in th e 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 w ere remarkably active, and their maximum densities reached 22,000 to 3 4,000 individ./ml (Exp. I) and 9,000 to 13,000 individ./ml (Exp. II).