Selection of bacteria enhancing the growth rate of axenically hatched rotifers (Brachionus plicatilis)

The effect of bacterial strains on the growth rate of rotifers, Brachionus plicatilis, was determined under monoxenic conditions. The first objective was to obtain sterile rotifer cultures starting from rotifer resting eggs using merthiolate or glutaraldehyde as disinfectant. Sterile rotifer cultures were obtained, without affecting the hatching ability of the resting eggs, when 0.05 mu l/l glutaraldehyde was used. This disinfection procedure was used to examine the effect of 20 bacterial strains, isolated from well-performing live-feed production systems, on the population growth rate of rotifers cultured under monoxenic conditions. Five out of the 20 bacterial strains tested were able to improve significantly the asexual reproduction of rotifers. The population growth rate (mu(pop)) of rotifer cultures treated with GR 12 and GR11 (respectively 0.664 +/- 0.043 and 0.622 +/- 0.062) was significantly higher than the mu(pop) of the control treatment (0.512 +/- 0.101). Overall, the egg ratio after 48 h was significantly higher in the cultures inoculated with the bacterial strains than in the axenic control treatment. The results show that it is possible to control the microbial community in rotifer cultures started from disinfected resting eggs by adding bacterial strains which have a positive effect on the population growth rate. (C) 1999 Elsevier Science B.V. All rights reserved.