Induction of allotriploids in the hybrids between Oreochromis niloticus ♀ Sarotherodon melanotheron ♂ was investigated by cold shock. To identify the treatment optima for triploidy induction, the temperature (T), duration (D) and timing after-fertilization (TA) of cold shocks were altered. In the treatment with 9 ℃ and 30 min duration, when inductions were applied after 10 min, no triploid was found; In the treatment applied 7 min after fertilization and with 30 min duration, 100% triploid rate was found between 5 ℃ to 9 ℃. In the treatment applied 7 min after fertilization and with 9 ℃, when duration time was over 60 min, the hatching rate was 0. Trials suggested the following treatments to be close to the optima:9 ℃, 30 min duration, applied 7 min after fertilization. The triploid rate reached 98.3%-100%,the corresponding hatching rate ranged from 17.5 to 19.1%.In most cases, allotriploid individuals were more variable (hatching rate: 9.6%-19.1%) than diploid hybrid (hatching rate: 7.6%-8.5%).