Histological Changes in Cuticle of the Red Swamp Crayfish, Procambarus clarkii During Molting Cycle

The present study was carried out to investigate histological changes in cuticle structure of the red swamp crayfish, Procambarus clarkii and number of layers of carapace cuticle during different molting stages. The crayfish samples were collected alive from the River Nile tributaries at Al-Kanater Al- Khairiya, Qalyoubiya Governorate during the period from spring 2010 to autumn 2011. These specimens were transported to the laboratory in the Faculty of Science, Al-Azhar University, Nasr City, Cairo. From the collected samples 10 individuals were selected according to molting stages morphologically, they were sexually mature and varied from 6.0 to 10.5 cm in standard length, 6.5 to 11.5 cm in total length and from 9.1 to 48.25 g in total body weight. These specimens were classified into five molting stages to study cuticle structure histologically. During intermolt stage, carapace integument is composed of four distinctive layers. These layers arranged from the outer surface to inner side as: epicuticle, exocuticle, endocuticle and membranous layer, respectively. During this stage, the epidermal layer composes of cuboidal epithelium. At the onset of premolt, a new endocuticle was arose above the membranous layer represents the new carapace. It was characterized externally by a clear separation called an apolysis occurred between an old endocuticle and new one. During an ecdysis, both of pre-ecdysal cuticle and postecdysal one were distinct, pre-ecdysal cuticle comprises epi-, exo-, and endocuticle; while the postecdysal composed of epi- and endocuticle only (without exocuticle), in addition to membranous layer, the epidermis was composed of elongated columnar epithelial cells. All these results indicated that the cuticle structure changes obviously during the course of molting cycle in fresh water crayfish P. clarkii.