Aims: To gives information's about internal changes associated with molting process of crayfish, Procambarus clarkii, from the Egyptian freshwaters. Internal changes in crayfish P. clarkii were studied from hatchlings to adult stage associated with molting cycle included (a) Changes in inorganic components (biominerals) especially Ca, P & Mg and (b) Organic components especially total protein & total cholesterol.

Methodology: The specimens of the red swamp crayfish, P. clarkii, were collected alive from the River Nile tributaries at Al-Kanater Al- Khairiya, Qalyoubia Governorate during the period from May 2013 to September 2014 for investigate the internal changes during molting cycle. All specimens were kept for acclimatization under the laboratory conditions in the glass aquaria aerated with air pumps at room ambient temperature (21- 23 °C) and at pH ranged between 7.3- 7.5. Water was exchanged weekly with aerated water under the same conditions.

Results: Data revealed that, internal changes in adult crayfish, P. clarkii, involved physiological changes as; the molting stages were also characterized by internal changes, represented by sharp fluctuations in the levels of biominerals and organic components in hepatopancreas, muscle and haemolymph which play an important role in molting cycle. The present study declared that, the increasing of biominerals in haemolymph in narrow range indicating the fact that haemolymph is not storage organ but is the carrier one. Also, data showed that, hepatopancreas plays an important role during the molting process and considers a main storage site for the most important inorganic and organic components. Statistical analysis indicated that, there are differences ranges in organic and inorganic components between the different molting stages.