Effects of low salinity stress on microstructure of gill and hepatopancreas and family survival rate of Portunus trituberculatus

The effects of low salinity on the microstructure of gill and hepatopancreas and family survival rate of Portunus trituberculatus were studied.The results showed that low salinity(15.0,13.0,11.0and 9.0)stress induced changes in microstructure of gill and hepatopancreas.At salinity of 15.0,the epithelium thinned slightly,and more B cells appeared in hepatopancreas tubules;At salinity of 13.0,the gill filament thickened irregularly,the number of B cells increased while R cells decreased,and many vacuoles appeared;At salinity of 11.0, disintegration of the epithelium was observed,the amount of haemocytes cells increased in gill cavity,and vacuoles in cytoplasm of columnar cells increased;At salinity of 9.0,epitheliumwas destroyed,even disassembled seriously,the number of vesicle shuttle in B cells increased and their volume enlarged,and the structure of hepatocytes was damaged seriously.Using the semi-lethal dose at 72hunder low salinity(LD50=11.1)as the evaluation index,low salinity tolerance of ten families at 24h,48hand 72hwas determined.No mortality was observed in the control during the experiment period.But the survival rate of the ten families decreased over time under low salinity stress,which was 64.44%-80.00%,50.00%-68.89%,and 33.33%-60.00%at 24h,48hand 72h,respectively.The ranking of survival rate of the ten families at 72hwas J10J4J9J5J7J3J6J2J8J1,which significantly lower than the respective controls(P0.05).