Sex differentiation by gonadogenesis and sex steroid hormones in cultured great sturgeon (Huso huso)

Fingerlings of 3 to 5 g weight of Huso huso were obtained from the Propagation Center of S. Rajaei sturgeon fish farm of Sari at the southern coastal part of the Caspian Sea, Iran. These fingerlings have been raised in small tanks first and then transferred to large circular fiober glass tanks supplied with ambient freshwater ranging in temperature from 12-27 degree C (according to the annual temperature cycle). The stages of gonad development were investigated through histological techniques while sex steroid hormones were determined by radioimmunoassy (RIA) using the "Diagnostica" kit for 17'-estradiol(E sub(2)) and Kavoshyar product for progesterone (P) and testosterone (T) determinations. Immature ovaries consisted exclusively of stage 1 and II follicles. In progressive developmental stages, external changes were distinguishable. This phase appeared for the first time in the gonads from some fish taken at 1.5-years of age (size about 60cm and weights of 1500 plus or minus 190g). In males, these stages were observed somewhat later (at about 2-years of age). Maturing stages that corresponded to stage III were recognized in fish of 2.5-years to 5year of age. The estradiol level was relatively low up to one year old fish. The E sub(2), T and 17,20'-P values were 0.23 ng ml super(-1), 0.8 ng ml super(-1) and 10 pg ml super(-1) , respectively. At the end of the second year, serum levels were still low with 17,20'-P and E sub(2) reaching 2.2pg ml super(-1) and 0.55 ng ml super(-1), respectively. It was possible to distinguish females at this stage but not males yet. Later, at an age of 2.5 years, both males and females entered the maturing stages (stage III) and gonads were already distinguishable by visual inspection.