The appropriate conditions to prevent the extrusion of the second polar body in eggs fertilized with normal sperm for triploidy induction or to restore diploidy in eggs activated with UV-irradiated sperm for gynogenesis induction in the sea bass were investigated. Shocks of 10 min duration at 0 degrees C starting 5 min after fertilization resulted in 100 per cent triploidy. Ploidy was determined by counting the number of nuclear organizing regions (NOR) of cells. Using these shock conditions, triploid sea bass were mass-produced, having an overall survival about 10 per cent lower than that of the diploid controls at one day post hatch (1 DPH). Similarly, the sex ratio in triploids was not different from diploids. To induce gynogenesis, the most suitable UV-dose to inactivate the sperm DNA was investigated. Currently, it remains to be determined whether triploid sea bass will outgrow diploids when the latter approach sexual maturation and also the percentage of females in the gynogenetic offspring.