The Effect Of KK-42on The Structure Of Cuticle In Macrobrachium Nipponense

Macrobrachium nipponense is a commercially important freshwater prawn for aquaculture inChina. For the first time, our laboratory has demonstrated that the treatment of imidazole derivative KK-42can significantly promote the growth of juvenile M.nipponense and shorten the molting cycle, but itsmechanism hasn’t yet clarified. The replacement of old cuticle by new one is an important event for ecdysis.Accordingly, the influence of KK-42on the exoskeleton structure of carapace and abdominal cuticle wasfirstly investigated by the histological methods, and the N-acetyl-β-D-glucosaminidase(NAGase) activityfrom hepatopancreas was quantitatively analyzed using ultraviolet absorption method befor and afterKK-42treatment.Prawns with body length of4.5±0.5cm were randomly divided into two groups: KK-42treatment group and control one. The prawns of KK-42treatment or control group were soaked for1min inKK-42solution at a concentration of1.95×10-4mol/L or0mol/L, respectively. The late premolt(D3)shrimps were used to do histological observation of carapace and abdominal cuticle at1、3、5、7、9d aftertreatment, meanwhile measuring the thickness of each layer of the exoskeleton. Select enoughpremolt(D0-4) M. nipponense and collet their hepatopancreas at0、6、12、24h after treatment, and measureits NAGase activity; select the shrimps during every stage and do histological observation of carapace beforKK-42treatment. The experiments above were performed in three replicates. The results are as follows:The cuticle is divided into two layers from the outside in, namely exoskeleton and epithelium.The carapace of intermolt M.nipponense is divided into three layers: epicuticle、exocuticle and endocuticle.PAS and hematoxylin staining results revealed that epicuticle is thin, about1/9-1/10of exoskeletonthickness, which is red homogeneous structure; exocuticle is thicker, about2/5-1/2of exoskeleton thickness,which is aubergine layered structure; endocuticle is the thickest layer, about1/2-3/5of exoskeletonthickness, and it’s loose structure and is stained pink. In addition, epicuticle and exocuticle are fomed inpremolt, while endocuticle is formed after molt. The height of epithelium also changes by the molt cycle:the height is lowest during intermolt, while it is highest during premolt, especially the cells of D2phasereaches the peak, then is the cell of postmolt.The first day after KK-42treatment, the exocuticle thickness of carapace significantly increased compared with the corresponding control42.83％(P<0.05); the endocuticle thickness of carapacesignificantly increased compared with the corresponding control at3d(P<0.01) and9d(P<0.01);meanwhile the thickness of entire carapace significantly increased compared with the correspondingcontrol at3d(P<0.01) and9d(P<0.01). The thickness of abdominal exoskeleton is not obvious: thethickness of exocuticle significantly increased compared with the corresponding control at1d(P<0.05); thetotal thickness significantly increased compared with the corresponding control at9d(P<0.05). The heightof epithelial cells significantly increased compared with the corresponding control at3d(P<0.05).The NAGase activity of control group fluctuated in M. nipponense, the activity at6、12、24hsignificantly reduced compared with it at0h. after KK-42treatment, the NAGase activity significantlyincreased compared with the corresponding control at6h(P<0.01)、12h(P<0.01) and24h(P<0.01).In conclusion, our present study first demonstrated that KK-42treatment can significantlyincrease the thickness of carapace and abdominal cuticle, especially thickness of carapace endocuticle; andsignificantly increase NAGase activity of hepatopancreas.