The optimal conditions for the retention of the second polar body in sea bass eggs were investigated by altering the timing, intensity and duration of application of pressure and cold shocks. Treatment optima for cold shocks were 0-1 degrees C for 15-20 min at 5 min after fertilisation (a.f.) and 8500 psi for 2 min at 6 min a.f. for pressure shocks. Meiogenesis was obtained by fertilising eggs with UV-irradiated homologous sperm (32,000 erg mm(-2)) and pressure or cold shocking eggs as above. 100% triploidy was induced following definition of liable periods for the disruption of the meiotic spindle obtained in gynogenesis. Ploidy investigations were performed on experimental groups by flow-cytometry. Verification of uniparental transmission in meiogens was carried out by microsatellite marker loci analysis. This work highlights the degree of variation in individual responses of selected broodstock to these agents. Finally, some preliminary results on heterologous fertilisation in sea bass with potential applications for gynogenetic studies are also provided. (C) 2000 Elsevier Science B.V. All rights reserved.