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The bay scallop Argopecten irradians is a hermaphroditic marine bivalve, its geographical subspecies, A.i.irradians, has been successfully cultivated in Southern coast of China for about 16 generations since being first introduced to China in 1991.To determine the effects of self-fertilization on production traits of this isolated Bay-scallop population, 12 self-fertilized families and a mass-spawned group were produced in the present study.The hatching rate and the survival at larvae, juvenile, and adult stage of the offspring of mass-mated group were all significantly larger than that of 10 of the 12 selfed families examined, and not significantly different from that of other 2 selfed families.For newly hatched larvae on day 1, no significant difference in size was found among the self-fertilized families and the mass-spawned group.The shell length of mass-mated group on day 9, 30, 75 and 230 and the live weight on day 75 and 230 were always significantly larger than that of 9 of the 12 selfed families examined, and not significantly different from that of the other 3 selfed families.In addition, significant difference in survival, shell length and live weight were found among the 12 selfed families at all development stages.The present study indicated the occurrence of inbreeding depression for production traits in the closed population of Southern Bay-scallop A.i.concentricus and the necessity of avoiding inbreeding when creating a production program of scallop seed, though not all families are significantly affected by inbreeding.