relationships between gonad development and sex steroid levels at different ages in Acipenser schrenckii

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 17β-estradiol (E₂) levels ranged from T 1.1 to 3.4 nmol l⁻¹ (average 1.8 nmol l⁻¹), and E₂ 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 E₂ 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 E₂ 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 E₂ 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 E₂ 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.