Cherfas, N.B., Agricultural Research Organization, Fish and Aquaculture Research Station, Dor, Mobile Post Hof Hacarmel, 30820, Israel
Peretz, Y., Agricultural Research Organization, Fish and Aquaculture Research Station, Dor, Mobile Post Hof Hacarmel, 30820, Israel
Ben-Dom, N., Agricultural Research Organization, Fish and Aquaculture Research Station, Dor, Mobile Post Hof Hacarmel, 30820, Israel
Gomelsky, B., Agricultural Research Organization, Fish and Aquaculture Research Station, Dor, Mobile Post Hof Hacarmel, 30820, Israel
Hulata, G., Agricultural Research Organization, Fish and Aquaculture Research Station, Dor, Mobile Post Hof Hacarmel, 30820, Israel

The results of a series of experiments conducted in our laboratory on the ornamental common carp (koi), aimed at optimizing heat-shock chromosome-set manipulation procedures, are described. The timing of heat-shock initiation was expressed in the relative unit of embryological age (τ0) in order to standardize this parameter, the absolute time for heat-shock initiation being calculated from duration of one τ0 at two different pre-treatment water temperatures. Heat shocks were applied within the periods of 0.05-0.60 τ0 and 1.20-2.20 τ0 which, respectively, cover the successive phases of the 2nd meiotic division and the 1st cleavage. The highest production of diploid gynogenetic offspring was observed when heat shocks were initiated at 0.15-0.25 τ0 and at 1.5 τ0, after insemination, corresponding to anaphase of meiosis-II, and metaphase of the 1st cleavage, respectively. Similar results were obtained irrespective of the different pre-treatment water temperatures, thus confirming the possibility of standardizing heat-shock timing by τ0. © 1994 Springer-Verlag.