Investigating the use of plasma testosterone and estradiol-17β to detect ovarian follicular atresia in farmed white sturgeon, Acipenser transmontanus

Abstract

To improve quality and yield of caviar in farmed white sturgeon it is essential to correctly assess the stage of ovarian maturity and avoid harvesting females with atretic ovarian follicles. To detect atresia by changes in blood plasma sex steroids, individual females (N = 10) in the late phase of oogenesis were repeatedly bled and their ovaries biopsied before and after onset of ovarian atresia. Follicular atresia was induced by transferring females from cold (10–13 °C) to warm water (20 °C). Ovarian follicle diameter increased and oocyte polarization index decreased in sampled fish over time. Plasma testosterone concentrations in fish with normal follicles were significantly higher, compared to fish with early histological signs of follicular atresia, such as structural changes in the chorion. Plasma estradiol concentrations declined to below detection limit prior to histological signs of atresia in 55% of the fish. Ninety five percent of fish with normal ovarian follicles and 93% of fish with atretic ovarian follicles were correctly classified using a discriminant function analysis based upon plasma testosterone concentrations. Logistic regression models were developed to predict the probability of normal ovaries based on plasma concentrations of sex steroids and can be further refined to improve selection of fish with normal ovaries for caviar harvest.