The histological developments of the gonad and the associated sex steroid levels were determined in the breeding stocks of Acipenser schrenckii (age classes 1 to 5) maintained under natural temperature regimes (December 4°C; August 26°C). Early sex differentiation was observed in 1-year-old fish, while testosterone (T) and 17b-estradiol (E 2 ) levels ranged from T 1.1 to 3.4 nmol l )1 (average 1.8 nmol l )1 ), and E 2 varied from 24 to 85 pmol l )1 (av. 50.3 pmol l )1 ). Gonadal status of 2-year-old males was in stage II while ovaries were at stage I, exhibiting T levels from 1.2 to 4.4 nmol l )1 (av. 2.2 nmol l )1 ), and E 2 concentrations from 10 to 97 pmol l )1 (av. 38.9 pmol l )1 ). At the age of 3 years, the testes in males were at developmental stage III while the ovaries remained in stage I, with T levels ranging from 1.3 to 21.7 nmol l )1 (av. 9.6 nmol l )1 ), and E 2 concentrations ranging from 17 to 108 pmol l )1 (av. 44.8 pmol l )1 ). At the age of 4 years, testes in males were at developmental stage III while ovaries in females had reached stage II, with T concentrations ranging from 7.3 to 52.6 nmol l )1 (av. 26.3 nmol l )1 ), and E 2 levels between 13 and 86 pmol l )1 (average 55.3 pmmol l )1 ). In 5-year-old fish, the testes reached maturity stage while the ovaries were mostly in stage III, with T values from 5.7 to 44.2 nmol l )1 (av. 13.9 nmol l )1 ), and E 2 concentrations from 21 to 453 pmol l )1 (av. 137.7 pmol l )1 ). Data demonstrated large differences in sex steroid levels among immature Amur sturgeon, and testicular maturation occurred earlier than ovarian maturation.

The objective of the study was to assess the changes of vitellogenin (Vg) during the course of the reproductive cycle in Amur sturgeon (Acipenser schrenckii). Vg was purified from the serum of vitellogenic female Amur sturgeon by distilled water and gel filtration. Vg had an apparent molecular mass of 410 kDa and appeared as one band corresponding to 205 kDa after SDS-PAGE under reducing conditions. These bands were immunoreacted in Western blotting using antiserum against amur sturgeon lipovitellin (anti-Lv) which is an egg yolk protein derived from Vg. Lv was purified from egg extracts by ammonium sulfate solution and gel filtration. Vg was confirmed to be a lipoglycophosphoprotein by staining with Red oil, Molecular ProesÕ Pro-Q Ò Emerald 300 Glycoprotein Gel stain and Pro-Q Ò Diamond Phosphoprotein Gel Stain. Vg induction was detected after injection of E 2 at a concentration of at least 0.5 mg kg )1 , and the plasma Vg concentration was increased by injection of the animals to 0.5 mg kg )1 for 5 day late. Immature sturgeons at 1015 g weight do not naturally synthesize Vg, but strongly responded to exogenously added E 2 . In addition, if they were not stimulated with exogenous E 2 , the youngest sturgeons did not show any detectable amount of Vg in their plasma, suggesting that Amur sturgeons with a body mass range of 903-1015 g could be used for the induction test, irrespective of their sex. The Enzyme-linked immunosorbant assay for sturgeon vg was developed to quantify serum Vg, using purified sturgeon Vg and anti-Vg. The measurable range was from 16.25 to 1000 ng ml )1 . The dilution curve in ELISA of vitellogenic female serum was parallel to the standard curve of purified Vg. The coefficient variations of intra-and inter-assay were less than 5%, respectively. Vg levels varied throughout natural vitellogenesis from 0 lg ml )1 (1-3 years old) to approximately 200 lg ml )1 (7-8 years old). We observed an early transitory peak of serum Vg levels 200 lg ml )1 (for 10 months) at the time of early vitellogenesis and high Vg levels 218 lg ml )1 (for 3 months) in spring period before ovulation. It appears that the duration of vitellogenesis in Amur sturgeon is lasting more than 2 years.

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