The Effect Of Crab Hemigrapsus Penicillatus On The Transmission Of White Spot Syndrome Virus(WSSV)

The habit and reproductive biology of crab Hemigrapsus penicillatus are preliminarily investigated The effect of crab H. penicillatus on the transmission of White Spot Syndrome Virus(WSSV) is studied. The chief results are as follows:1. The habit and reproductive biology of crab Hemigrapsus penicillatus are preliminarily investigated. The relationship between egg-canying amount (Q) and carapace width (L) is 0=865.821-7275 (r=0.97). Five zoea stages and one megalopa stage are observed before the Larva developed into the first stage of junior crab. The accumulative temperature for embryo, 2oealarva and megabpa larva development is 219.4℃, 226.35℃, 49.3℃ respectively (12℃ as biological zero degree). l2. High positive rate is detected in natural collection crabs. The positive rate of natural collect Brood crabs of H. penicillatus, eggs, zoea larva, megalopa larva and junior crab is 82.7%, 79.3%, 72%, 0 and 42.5% respectively. The positive rate of crab H. tridens, eggs, crab Macrvphthalmus (Macreotis)japonicus is 46.25%, 66.7%, 60% respectively.3. Crab H. penicillatus is exposed to WSSV by oral route. After 3d, the food consumption has an obvious decrease and after 15d some crabs move tardy, react torpid to stimulus and its carapace shows yellow color. After 30d, the mortality of the crabs in experiment group is 50% and no crab die in control group. In experiment group's three replications the positive rates of the crabs are 75%, 70% and 45% respectively, howevei; in control group all crabs show WSSV negative by dot-blot hybridization.4. Health shrimp Litopeneuas vannamei is challenged by feeding with WSSV positive H. penicillatus and cohabitation with WSSV positive crab H. penicillatus. All shrimps die in lOd after feeding with positive crab H. penicillatus and show WSSV positive rate in experiment group by dot-blot hybridization. In cohabitation experiment group, the mortality of shrimps in three replications are 90%, 100% and 100% after 10 days. No shrimp in the control group dies and shows WSSV positive by dot-blot hybridization.5. Three kinds of feces of Hpenicillatus are used to challenge the health shrimp. The first kind of feces is expelled by H. perictilatus which is fed with normal food. The other kind of feces is expelled by H. penicillatus which is fed with WSSV positive shrimp. The third kind of feces is collected beginning fiom the 4th day after H penicillatus is first fed with WSSV positive shrimp three days and then is fed with normal food. The feces samples are WSSV negative by dot-blot hybridization and in the feeding experiment the shrimps prefer to eat the feces but do not show apparent WSS. The shrimp samples are also negative by dot-blot hybridization.