Androgenesis is defined as all2paternal inheritance. Viable androgenetic diploids can be generated by inhibiting the first cleavage to double paternally derived chromosomes ,after fertilization of genetically inactivated eggs with normal sperm. It is a technique that could facilitate the production of completely homozygous isogenic lines, examine sex determination, make genetic analysis, and protect endangered species. Gamma and X2rays inactivation are the usual methods used to inactivate egg nuclei. However, since special facilities are required to manage radioactivity safety, these methods are not practical for routine induction of androgenesis. In many fish species, efficient procedures of genetically inactivating eggs and restoring diploidy have been studied and achievements of successful diploid androgenesis were reported. In contrast , in mollusks , there were only a few reports of cytobiological studies on one species of spontaneous androgenetic Corbicula leana , artificial induction of androgenesis has rarely been studied. Chlamys f arreri is a main cultured mollusk species in China , as well as an important object of study in mollusk breeding science. In this study , optimum conditions of ultraviolet (UV) ray irradiation for genetic inactivation of eggs were examined to develop simple and safe techniques to induce haploid androgenesis in C. f arreri . Mature cultured C. f arreri were collected locally in late March and early May from the coast of Weihai , Shandong. Eggs and sperm were obtained by artificially inducing spawning with the stimulations of dryness and raising water temperature from 16 to 20?C. Discharged eggs were collected by suction and rinsed in filtered seawater several times. Suspensions of sperm and egg were prepared at concentrations of 1. 0 ?106 sperm per mL and 1. 0 ?104 egg per mL by dilution with filtered seawater. Egg suspension (4 mL ) was spread on a plastic Petri dish and treated with the UV rays (254 nm) at intensity of 2. 8 mW?cm -2 ?s-1for 0, 5, 10 ,15 ,20 ,25 ,30 ,35 ,40 ,45 ,50 ,60 ,or 70 s. Onthecompletionofirradiation,eggsuspensionwasmixed -20 ℃. recorded and samples of with normal sperm (0. 5 mL ) and transferred to group were The fertilization rate was a baker for culture at temperature of 19 During the culture, the fertilization and development rates of each the larvae (trochophores) were collected to determine the ploidy of embryos. The result showed that the ultraviolet ray was effective for inactivating egg chromosomes. relatively high (60. 2 %) and the developmental rate became zero when eggs were irradiated for haploid was the highest (49. 2 %) . 20 s at UV intensity of 2. 8 mW?cm -2 ?s -1and mixed with normal sperm. The results of chromosome observation showed that under this condition the rate of This result indicated that irradiation for 20 s at UV intensity of 2. 8 mW? cm -2?s -1 was the optimum dose to achieve haploid androgenesis in this kind of scallop. The fertilization rate decreased with increasing irradiation time. This is probably because with the increasing of irradiation dose , the degree of damage of some important factors that control the fertilization potency of eggs and the development of embryos increased. It was also observed that the development of D2shaped larvae decreased with increasing irradiation time , and the development of the genetically inactivated eggs fertilized with the normal sperm terminated before reaching the D2shaped stage. Aneuploids were found in this study. Because ultraviolet irradiation is known to cause pyrimidine dimerization in the DNA helix , which prevents the replication of genome , the occurrence of these aneuploids is probably attributed to different degrees of maternal chromosomal inactivation by UV irradiation and/ or DNA repair.