Meiogynogenesis of the African catfish (Clarias gariepinus) was optimized by altering the intensity, duration and timing of application of pressure, heat or cold shocks shortly after activation of the egg with sperm which had been genetically inactivated with UV irradiation. The distributions of the survival rates showed a unimodal (heat and hydrostatic pressure shock) or bimodal (cold shock) pattern and were specific to each treatment. The timing of the expulsion of the second polar body invariably occurred 3 to 5 min after fertilization. Of the three methods tested, cold (5 degrees C, during 40 min at 3 min post-activation) and pressure (55.00 MPa during 2 min at 3 min post-activation) shocks turned out to be the most efficient in terms of survival rate. A relative hatching rate of up to 81% of gynogenetic diploid fish was achieved. The final proof of gynogenetic status was made with a paternity test by means of multiple-locus DNA fingerprinting.