Pruginin, Y., Fisheries Division, Extension Service, Ministry of Agriculture, Tel-Aviv, Israel
Rothbard, S., Fish Breeding Farm, Gan-Shmuel, Israel
Wohlfarth, G., Fish and Aquaculture Research Station, Dor, Israel
Halevy, A., Fish and Aquaculture Research Station, Dor, Israel
Moav, R., Department of Genetics, The Hebrew University, Jerusalem, Israel
Hulata, G., Department of Genetics, The Hebrew University, Jerusalem, Israel

The proportion of males in single pair crosses between Tilapia nilotica females and T. aurea males was found to vary between 50 and 100%. There was no apparent influence of the T. aurea males on these proportions. In a similar test nine T. vulcani females were paired with T. aurea males, and the proportion of males in their hybrid offspring ranged between 93 and 98%. Two T. nilotica mothers of all-male hybrid broods mated with unselected T. nilotica males, and all their daughters also reproduced all-male hybrid broods when crossed with T. aurea males. The reciprocal cross of T. aurea females with T. nilotica males reproduced three males to each female offspring. Growth rate tests of the all-male T. nilotica × T. aurea hybrids, and the T. vulcani × T. aurea hybrids did not reveal heterosis. © 1975.