Hulata, G., Agricultural Research Organisation, Fish and Aquaculture Research Station,Dor, Mobile Post Hof Hacarmel 30820 Israel
Wohlfarth, G.W., Agricultural Research Organisation, Fish and Aquaculture Research Station,Dor, Mobile Post Hof Hacarmel 30820 Israel
Halevy, A., Agricultural Research Organisation, Fish and Aquaculture Research Station,Dor, Mobile Post Hof Hacarmel 30820 Israel

Two generations of mass selection for rapid growth were performed on juvenile and adult Oreochromis niloticus. A special procedure was developed for producing broods of equal-aged individuals. Response was tested after one and two cycles of selection by comparing the progenies of selected fish to those of two controls. Mean weight gains of the "random sample" control groups were 4% and 11% lower than those of the "original parent" control group in the first and second growth tests, respectively. Mean weight gain of the "original parent" control was equal to that of progeny of fish selected at adult age, but higher than weight gain of progenies of fish selected as juveniles. No improvement over the original base population was achieved by selecting for growth. © 1986.