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 wa s 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 res ting eggs were produced only at two salinities (9 parts per thousand a nd 18 parts per thousand) and that their number was affected by the am ount of food provided. A model consisting of two generalized linear su b-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 productio n: one related to the presence or absence of resting egg production, a nd the other to the number of resting eggs produced, given that produc tion had occurred. Besides indicating the best combination of salinity and food concentration for obtaining large numbers of resting eggs, t hey 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 pr oduction of resting eggs. The results of the present study help in def ining the optimal conditions for mass production of resting eggs, whic h are of potential importance in aquaculture.