Hulata, G., Agricultural Research Organization, Institute of Animal Sciences, Fish and Aquaculture Research Station, Dor, D.N. Hof Hacarmel 30820, Israel
Wohlfarth, G., Agricultural Research Organization, Institute of Animal Sciences, Fish and Aquaculture Research Station, Dor, D.N. Hof Hacarmel 30820, Israel
Rothbard, S., Agricultural Research Organization, Institute of Animal Sciences, Fish and Aquaculture Research Station, Dor, D.N. Hof Hacarmel 30820, Israel

Prolific and uncontrolled reproduction of tilapias in production ponds is one of the most serious limitations in tilapia culture. Monosex culture by manual sexing is a practical method to overcome this problem, but requires skilled manpower and is time consuming and wasteful. The early promise of a genetic solution by the use of interspecific all-male hybrids has not been realized on a commercial scale due to broodstock management problems. None of the existing genetic models for sex determination is capable of serving as a breeding tool. Furthermore, intrapopulation variation for sex determination was demonstrated in Israeli populations of Sarotherodon aureus and S. niloticus. In order to obtain reliable broodstocks for commercial production of all-male S. niloticus × S. aureus hybrids, single pairs consisting of a female from one species and a male from the other are progeny-tested. The selection criterion used is the sex ratio in the hybrid progenies of these interspecific crosses. In crosses involving a S. niloticus female and a S. aureus male, all-male progenies are required for selecting the parents. In the reciprocal crosses the required sex ratio is 1 female: 3 males. Preliminary results confirm that some, but not all, S. niloticus × S. aureus pairs yield all-male progenies. © 1983.