Karplus, I., Department of Aquaculture, Agricultural Research Organization, Volcani Center, Beit-Dagan, Israel
Milstein, A., Department of Aquaculture, Agricultural Research Organization, Volcani Center, Beit-Dagan, Israel, Fish/Aquaculture Research Station, Dor, M.P. Hof HaCarmel, 30820, Israel
Cohen, S., Department of Aquaculture, Agricultural Research Organization, Volcani Center, Beit-Dagan, Israel
Harpaz, S., Department of Aquaculture, Agricultural Research Organization, Volcani Center, Beit-Dagan, Israel

Production characteristics and profitability of three carp- tilapia stocking ratios (1:1, 1:2 and 1:5) were compared in a semi- intensive polyculture system. The experiment was carried out at the same total stocking density of 1 fish m2 earthen ponds. Common carp, Cyprinus carpio L., and a tilapia hybrid, Oreochromis niloticus (L.) x O. aureus (Steindachner), were stocked at a joint density of 900 fish per pond, while grass carp, Ctenopharyngodon idella (Cuvier and Valenciennes), and silver carp, Hypophthalmichthys molitrix (Valenciennes), were each stocked at 50 fish per pond in all treatments, mean harvested weights of both common carp and the tilapia hybrid were markedly decreased upon the increase in density of their own species. Survival of all four species was over 80% in all three carp- tilapia stocking ratios. The differences in relative profitability of the three carp-tilapia stocking ratios did not exceed 10% on the basis of 1991 prices. However, based on 1994 prices, relative profitability of the 1:2 and particularly, the 1:5 carp-tilapia stocking ratio were 35% and 41% higher than the 1:1 ratio, respectively. This was because of the increase in the price of large carp and tilapia of all sizes, and a decreases in the price of small carp.