Gomelsky, B., Agricultural Research Organization, Institute of Animal Science, Department of Aquaculture, Dor, Mobile Post Hof Hacarmel 30820, Israel
Cherfas, N.B., Agricultural Research Organization, Institute of Animal Science, Department of Aquaculture, Dor, Mobile Post Hof Hacarmel 30820, Israel
Peretz, Y., Agricultural Research Organization, Institute of Animal Science, Department of Aquaculture, Dor, Mobile Post Hof Hacarmel 30820, Israel
Ben-Dom, N., Agricultural Research Organization, Institute of Animal Science, Department of Aquaculture, Dor, Mobile Post Hof Hacarmel 30820, Israel
Hulata, G., Agricultural Research Organization, Institute of Animal Science, Department of Aquaculture, Dor, Mobile Post Hof Hacarmel 30820, Israel

Hormonal sex inversion was induced in genotypic females of the Israeli Dor-70 common carp line and ornamental common carp (koi). All-female progenies produced by either meiotic or mitotic gynogenesis were investigated in the experiments. Twenty-seven to 40-day-old fingerlings (mean initial weight of 2.8-14.5 g) were fed with a diet containing 100 ppm methyltestosterone for 40 days. The effectiveness of androgen treatment depended on fish rearing conditions. The percentage of inverted males varied from 46.7 to 96.6% among fish reared in recirculation water systems, and from 20.0 to 43.8% among fish reared in tanks with running water. The data obtained suggest that the weight of fish (rather than their age) may be used as a practical criterion for determining the appropriate period of androgen treatment. © 1994.