A MODEL EVALUATING THE CONTRIBUTION OF ENVIRONMENTAL-FACTORS TO THE PRODUCTION OF RESTING EGGS IN THE ROTIFER BRACHIONUS-PLICATILIS

The production of resting eggs by the rotifer Brachionus plicatilis was tested at four salinities (9, 18, 27 and 36 parts per thousand) and six concentrations of the alga Chlorella stigmatophora (0.25, 0.5, 1.0, 2.0, 4.0 and 6.0 x 10(6) cells ml-1). The results indicated that resting eggs were produced only at two salinities (9 parts per thousand and 18 parts per thousand) and that their number was affected by the amount of food provided. A model consisting of two generalized linear sub-models was built to evaluate the contribution of each of the tested food concentrations at the two salinities. The sub-models were used to distinguish between two different components of resting egg production: one related to the presence or absence of resting egg production, and the other to the number of resting eggs produced, given that production had occurred. Besides indicating the best combination of salinity and food concentration for obtaining large numbers of resting eggs, they revealed the contribution of internal population factors that were not controlled in the course of the experiment. The model identified the positive contribution of the relative number of females to males, and the negative association between high rotifer densities and the production of resting eggs. The results of the present study help in defining the optimal conditions for mass production of resting eggs, which are of potential importance in aquaculture.