We studied the possible role that marine microalgae may play during the outbreaks of acute viral necrobiotic disease(AVND)of cultured zhikong scallops(Chlamys farreri).In order to elucidate the possibility of marine microalgae carrying AVNV(acute viral necrobiotic disease virus),seventeen species of microalgae were co-cultured with pure AVNV solution and were assayed daily by PCR to study whether they could carry AVNV. Further experiments were conducted to investigate whether the virus carried by microalgae could reinfect zhikong scallops.The results showed that 6(including Platymonas subcordiformis,Chlorella sp.,Dunaliella viridis,and Tetraselmis tetrathele in Chlorophyta and Nitzschia closterium minutissima, and Skeletonema costatum in bacillariophyta)of 17 microalgae,which account for 35.3% of the tested algae,could carry AVNV,the AVNV detections in microalgae were positive during 96 to 144 h.The 6 AVNVmicroalgae complex were fed to zhikong scallops,the tested scallops show a typical acute viral necrobiosis symptom,and the accumulated mortalities of scallops fed with the AVNVmicroalgae complex were significant(P<0.05)or highly significant(P<0.01)compared with that of the control fed with mixture with 6 species microalgae during the nineday experiment,which indicated that the AVNVmicroalgae complex have an impressing ability to infect the scallops.Based on these laboratory challenges studies,the microalgae can serve as a vector in the horizontal pathway of transmission of AVNV via feeding or filtering process of scallops.