Rotifers do not like stress. They like stable conditions and do tremendously better when all system parameters remain stable for weeks on end.
Stress can be result from low oxygen, prolonged feed loss (several hours) salinity changes, pH shock, temperature, ammonia spikes and numerous other factors. These factors compound each other resulting in stress when a single variable alone does not appear to be off enough to cause stress. Stress results in a reduction of egg production and subtle changes in the appearance of the rotifer. Stress can occur without noticeable rotifer death and can occur a day or more before a problem is even noticed.
Rotifers are more sensitive to stress than many Live Feed Personnel realize, even though they can survive a lot of abuse and continue to produce some eggs. Stress often permanently damages rotifers, reducing reproduction, health and resistance to pathogens. Because the rotifers alive at the time of the stress are permanently damaged, the culture will only return to full strength when the old rotifers are removed and new rotifers hatch to replace them. This process can take many days. In the mean time, these stressed and minimally productive rotifers remain in your culture, consume food and look like they are healthy. See Table below:
Table E.8: The percent of old, damaged rotifers 4 days after a stress event at different harvest rates.
Rotifers recover slowly (see below). It is not uncommon for rotifer cultures to experience repeated mild stress that goes unnoticed by live feeds personnel. In these cases rotifer production continues and seems normal, but the rotifers do not reach their full potential and remain susceptible to crashes and pathogens.
It is not uncommon for rotifers to require a week or more to recover form a stress event. If your rotifers experience one stress event per week, even a mild stress event, your rotifers will never achieve their potential and their reduced productivity may come to be seen as normal.