Sporadic diploid gynogenetic fry resulted from fertilization with y-irradiated
sperm. Their frequency increased appreciably when thermal shock treatments, beginning
during the first hour of development (―0.4 OC lasting 6 hrs 45 min ; 26-30 °C lasting 10 min),
were used. When the eggs were fertilized with normal sperm, a good triploidization rate
was induced by means of heat shocks (27-30 °C lasting 10 min). It is supposed that the retention
of the second polar body caused the gynogenetic diploidy observed.