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.