SUMMARY1. We offeredScenedesmus obliquusin five densities, from 0.5 to 8 ± 106cells ml−1, to the rotiferAnuraeopsis fissa. Growth rates (r) during the exponential phase (first 7 days) were significantly and positively related to food density. Thervalues (mean ± SD) varied between 0.454 ± 0.067 and 0,856 ± 0.090, from the lowest to the highest food concentration, respectively. Population growth went through a phase of exponential increase which lasted from 7 to 10 days before a plateau and, in some cases, a decrease occurred.2. There was a linear relation between food density and rotifer plateau density. At the highest food density, a peak abundance (mean ± SD) of 2312 ± 226 individuals ml−1was reached, while at the lowest food density there was no identifiable single peak but a plateau, at a density of 361 ± 62 ind. ml−1.3. The egg ratio decreased with increasing population density. The ratio of loose eggs to eggs attached to females indicated that more eggs became detached at higher food densities.4. As in many other rotifer species studied so far, population density ofA. fissawas less stable at higher algal food concentrations. Numerically,A. fissacould be grown at twice the density achieved