OVARIAN DEVELOPMENT AND CYCLES IN CULTURED SIBERIAN STURGEON, ACIPENSER BAERI

Sturgeon lack external sexual dimorphism and have longer-than-annual o varian cycles. Using gonadal biopsy of marked fish, we identified sex and monitored ovarian development in one cohort of cultured Siberian s turgeon over the age interval 8.5-12.5 year Sex ratio in the populatio n 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 greater than or equal to 2.8 mm (Group 2, spawnable) and anot her with smaller follicles in previtellogenic or vitellogenic growth ( Group 1). During the 5 year period of observations, 11.2 % of the init ial 268 females were lost. The oocytes of Group 2 exhibited migratory germinal vesicle but its position in animal hemisphere was not periphe ral 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 mole times during a period of study. exhibited biennial ovarian cycle or recurring cycles of I and 2 years in the same individual. Annual and triennial cycles were also o bserved. Some abnormalities in oocyte pigmentation are described. (C) lfremer-Elsevier. Paris.