THE EFFECT OF ENVIRONMENTAL FACTORS ON RESTING EGG PRODUCTION IN THE ROTIFER Brachionus plicatilis

The rotifer Brachionus plicatilis is widely used in aquaculture, but problems remain with its utilization. It is often difficult to synchronize rotifer production with larval demand, year‐round culture maintenance is a technical nuisance, and cross‐strain contamination is a persistent problem. Rotifers produce resting eggs that are thick‐walled encysted stages which can remain dormant for extended periods. These resting eggs are analogous to Artemia cysts and could be used in a similar fashion in aquaculture. The mass production of rotifer resting eggs depends upon our ability to manipulate the rotifer life cycle in mass cultures. This paper examines several factors regulating the rotifer life cycle and identifies environments that promote resting egg production. Depending on the rotifer strain used, the strongest mictic response occurs at moderate temperatures and salinities. A mixed diet of Chlorella and baker's yeast promoted the greatest resting egg production. The RUS B. plicatilis strain exhibited the strongest mictic response in all environments tested and was 5 times that of any other strain. Success in manipulating the rotifer life cycle for resting egg production will depend upon a thorough understanding of sexual reproduction and how it is integrated into the life cycle. The major problem currently limiting resting egg production in laboratory populations is fertilization rate. The prospects for the controlled mass production of rotifer resting eggs are nonetheless good, but they are not imminent.