Ovarian development and cycles in cultured Siberian sturgeon, Acipenser baeri

Abstract

Sturgeon lack external sexual dimorphism and have longer-than-annual ovarian cycles. Using gonadal biopsy of marked fish, we identified sex and monitored ovarian development in one cohort of cultured Siberian sturgeon over the age interval 8.5–12.5 year. Sex ratio in the population did not differ from 1:1 (268 females and 286 males). Each November, the females were separated into two groups: one with ovarian follicle diameter ≥ 2.8 mm (Group 2, spawnable) and another with smaller follicles in previtellogenic or vitellogenic growth (Group 1). During the 5 year period of observations, 11.2 % of the initial 268 females were lost. The oocytes of Group 2 exhibited migratory germinal vesicle but its position in animal hemisphere was not peripheral in November. The annual changes in proportions of Group 2 females, from 34.6 to 63.3 %, reflected ovarian cycles of different duration. Majority of 196 females, matured two or more times during a period of study, exhibited biennial ovarian cycle or recurring cycles of 1 and 2 years in the same individual. Annual and triennial cycles were also observed. Some abnormalities in oocyte pigmentation are described.