Induction of sexual reproduction and resting egg production in Brachionus plicatilis by a diet of salt-grown Nannochloris oculata

Abstract

Cultures of Brachionus plicatilis O.F. Muller were raised on different species of unicellular marine algae. Chlorella stigmatophora, Isochrysis galbana and Nannochloris oculata were evaluated as the best food plankton for population growth of B. plicatilis. N. oculata was selected for experiments on inducing sexual reproduction in the rotifers because of its ease in propagating and culturing. Under conditions in which the algal density, rotifer density, and environmental factors implicated in parthenogenesis remained constant, the algal quality was tested as the only variable for inducing sexual reproduction in the rotifers. N. oculata previously grown on salinities between 18–108‰ S was washed and fed to B. plicatilis in a seawater medium of 36‰ S. Sexual reproduction appeared in rotifers fed on algae grown on salinities above and below sea water level. Induction of sexual reproduction mostly occurred in rotifers that were fed on N. oculata propagated on salinities exceeding 54‰ S. The results are interpreted as indicating the production and accumulation in salt-grown N. oculata of factor(s) implicated in the sexual reproduction of B. plicatilis.