Cherfas, N.B., Agricultural Research Organization, Fish and Aquaculture Research Station, Dor, Mobile Post Hof Hacarmel, Israel
Hulata, G., Agricultural Research Organization, Fish and Aquaculture Research Station, Dor, Mobile Post Hof Hacarmel, Israel
Kozinsky, O., Agricultural Research Organization, Fish and Aquaculture Research Station, Dor, Mobile Post Hof Hacarmel, Israel

Experiments on timing of heat shock during the first cleavage in order to optimize induced diploidization of the chromosome set were conducted on ornamental (koi) carp, Cyprinus carpio L. The effect of heat shock on embryo survival and ploidy level was monitored in gynogenetic offspring and regular ones. Dimensionless measure of embryological age τ0 was used to express the time of heat shock application. The heat shock was initiated within the limits of 0.6-3.0 τ0 (0.9-2.0 τ0 in most experiments) after insemination. Incubation temperature prior to treatment was either 25°C or 20°C. Water temperature of heat shock was 39.3-40.5°C, and duration 2-3 min, in different experiments. Embryo survival is characterized by alternating "sensitive" and "non-sensitive" periods with lowest survival when heat shock initiation corresponds to 1.6-1.8 τ0. The highest frequency of 2n mitotic gynogenetic embryos (up to 15% relative to total number of inseminated eggs) was observed when heat shock was initiated at 1.5-1.6 τ0. © 1993.