en Biology & physiology Biology & physiology پژوهشي Orginal research papers This study was carried out with the aim of examining the seasonal reproductive cycle of the female crayfish Astacus leptodactylus from Aras Dam Lake, Western-Azerbaijan, Iran. Gonadosomatic index (GSI), and oocyte size were measured in females sampled seasonally in June, August, November(2011), January(2012). Development of the oocytes was categorized according to the diameter and the presence/absence of yolk granules. The ovary development was accompanied by increasing levels gonadosomatic index and egg diameter. Ovarian development histologicaly related to the seasonal GSI . This index was low in June (0.61±0.05) when oocytes started developing and reached the highest value in November (13.53±0.25), when vitellogenic oocytes were abundant in the mature ovary. Our results highlight the relationship between the ovary development and the GSI and egg diameter in the crayfish A.leptodactylus during the reproductive cycle and held important implications for the management of aquatic species. Thus, investigation of female A. leptodactylus reproduction is highly significant for fisheries managers as well as environmentalists concerned with perpetuating crayfish stocks. Astacus leptodactylus, ovarian development, gonadisomatic index, egg diameter, histological analysis, ELISA 103 111 http://jifro.ir/browse.php?a_code=A-10-1272-65&slc_lang=en&sid=1 S. M Mirheydari 10031947532846009656 10031947532846009656 Yes A Matinfar 10031947532846009657 10031947532846009657 No M Soltani 10031947532846009658 10031947532846009658 No A Kamali 10031947532846009659 10031947532846009659 No Y. A Asadpour-Ousalou 10031947532846009660 10031947532846009660 No S Safi 10031947532846009661 10031947532846009661 No M Paolucci 10031947532846009662 10031947532846009662 No