Abstract:In order to research the possible mechanism that the duration of molting cycle of the juvenile prawn Macrobrachium nipponense was shortened by KK-42,the cuticle structure of carapace was investigated by the histological method and the N-acetyl-β-D-glucosaminidase(NAGase)activity from hepatopancreas was quantitatively analyzed using ultraviolet absorption method before and after KK-42 treatment.The prawns with body length of (3.3±0.5)cm were randomly divided into two groups:KK-42 treatment group and control one.The prawns were soaked for 1 min in KK-42 solution at a concentration of 1.95×10-4 mol/L(KK-42 treatment group)or 0 mol/L(control group),respectively.Afterwards,the carapaces derived from late premolt(D3)prawns were chosen to be used for histological observation and thickness measurement of layered exoskeleton,meanwhile,the hepatopancreas NAGase activity in stage D3 M.nipponense was quantitatively analyzed.The results showed that the exocuticle thickness of carapace significantly increased by 42.83% compared with the corresponding control on 1st day after KK-42 treatment,and the endocuticle thickness as well as the whole exoskeleton thickness significantly increased by 70.72%(P<0.01),77.27%(P<0.01)and 38.69%(P<0.01),52.23%(P<0.01),respectively,compared to the corresponding control on the 3rd day and the 9th day after KK-42 treatment.A 31.69% rise in the height of epithelial cells was obtained on the 3rd day after KK-42 treatment compared with the corresponding control.The NAGase activity significantly increased by 42.53%(P<0.01),34.28%(P<0.01)和18.36%(P<0.05),respectively,at 6 h,12 h and 24 h after KK-42 administration compared to the corresponding control.The results reveal that KK-42 treatment can significantly increase the cuticle thickness of carapace,and promote NAGase activity from hepatopancreas.