The inhibition by ammonia of population growth of the rotifer, Brachionus rubens, in continuous culture

For the safe maintenance of microalgae and rotifers in mass culture, it is necessary to know the exact threshold concentration of ammonia for rotifers. In order to determine this threshold concentration, the continuous culture technique was used as a sensitive method to determine the influence of ammonia on the reproduction rate of the rotifer Brachionus rubens. As expected, only unionized (free) ammonia affected the population growth. Up to a concentration of 3 mg NH 3 -N l the reproduction of Brachionus was unaffected. In the range of 3–5 mg NH 3 -N l the reproduction rate decreased, although no animals were killed. This decrease was reversible and could be overcome by lowering the NH3-N concentration. At concentrations over 5 mg NH 3 -N l the rotifers died within 2 days.