ABSTRACT: In order to characterize a strain of the rotifer Brachionus plicatilis, description of the organism, different egg types, as also the main populational features of this stock were made. Besides, the effect of salinity on the behavior and population growth of the strain was studied. The isolated strain belongs to the 'S' morphotype, with an average lorical length of 183 µm. In individual microcultures (0.5 ml) fed with Chlorella sp., at a salinity of 25‰ and temperature of 28 °C, the stock had an average life of 6.6 days, with an average offspring of 15.2 individuals per day. The salinity affected the instantaneous growth rate, which could be observed in cultures with salinities ranging from 20, 35 and 50‰. All of these were previously acclimated and fed with yeast, which showed values of r = 0.31, 0.20 and 0.18, respectively. B. plicatilis showed visible morphological and physiological alterations in changes of salinities above 10‰. The optimal salinity for the best pupulation growth ranged between 10‰ and 20‰, in which the sexual phase (mixis) also occurred.