Maternal transfer of immune factors from mother to eggs has been reported in many aquatic species,and these factors played important immune roles in developing embryos and larvae.However,the study on maternal immunity of shellfish remains lacking.In this study,maternal transfer and bacteriostasis of a C-type lectin in scallop(Patinopecten yessoensis)were analyzed.We detected the mRNA expression pattern of the C-type lectin gene in ovary and early developing larvae using the real-time quantitative PCR method,and tested the antibacterial activity of maternal C-type lectin in eggs by colony-forming unit(CFU)assay.The results of qRT-PCR showed that the expression of C-type lectin gene in ovary after bacterial challenge was time-dependent,and it was up-regulated gradually from 2 h after injection of bacteria and reached the peak at 8 h which was 6.2 times compared to the control group,and then dropped progressively to the original level.On the other hand,the fact that mRNA was found both in the eggs and larvae indicated that it could be transferred from mother to offspring.The mRNA expression in bacterial challenge group was significantly higher than those in normal group except for the 36 h point.The CFU assay revealed that the cytoplasm of eggs with protein concentration of 200 μg/mL and 400 μg/mL had lethal effect on the bacteria Vibrio anguillarum,and the function weakened significantly once the antibody of C-type lectin was added,which indicated the C-type lectin from mother had antibacterial activity.It is concluded that the maternal C-type lectin can transfer from mother to the offspring and has antibacterial activity.