According to the concise definition of Thorgaard (1986) androgenesis is an all paternal type of inheritance, where the genetic material of the egg cell does not contribute to that of the embryo. Therefore, androgenesis is a technique that could facilitate the rapid production of completely homozygous isogenic lines of fish. Androgenesis was induced in O. niloticus by fertilizing UV-irradiated eggs with untreated sperms and then blocking the first cleavage division with heat shock. The optimized UV exposure period, based on the complete absence of diploids 48 hours post fertilization, was 15 minutes when a distance of 27.5 cm being kept between the UV lamp (245 nm) and the eggs. The haploidization nature of the embryo was tested by chromosome counts in 48 hour after fertilization embryos. Diploidy was restored by suppression of the first cleavage division using a heat shock of 41oC. Heat shock treatment of 4.5 minutes duration applied after 26 minutes from fertilization gave 0.68% survival to yolk sac resorption stage.