Early identification of sex in cultured white sturgeon, Acipenser transmontanus, using plasma steroid levels

In sturgeon aquaculture, it is advantageous to sex fish as early as possible so that males can be used for meat production and females reserved for caviar production. Currently, growers wait 3 to 4 years before fish are sexed by an invasive surgical examination of the gonads. The goal of this study was to determine when sex could be determined by examining levels of plasma steroids. Populations of white sturgeon were held at three locations and water temperatures (Oregon-13+/-0.1°C, Idaho-15 +/-0.1°C and California-18+/-0.5°C). Blood was sampled every 3 months and plasma testosterone (T), 11-ketotestosterone (KT) and estradiol (E2) concentrations were measured by radioimmunoassay (RIA). By 18 months of age, males from California had significantly higher levels of T and KT than females. By 21 months, all males could be separated from females based on T and KT content (>2 ng/ml). However, males and females from Idaho and Oregon had similar levels of T and KT up to 36 and 34 months of age, respectively, and sex could not be delineated based on plasma sex steroid content. There were no differences in E2 levels between males and females in all populations, and at all sample periods. Histological analysis of gonads revealed that all but one of the males from California had well differentiated testes with spermatogonia undergoing mitosis in cysts (stage 2), whereas the testes of all fish from Idaho and Oregon had just begun to differentiate (stage 1). Growth rates of fish were highest in California, intermediate in Idaho and lowest in Oregon. It appears that proliferation of spermatogonia is necessary for production of androgens and that growth rate, as influenced by water temperature, is the main contributor to the early onset of this process. This study has developed a less invasive technique for ascertaining sex in white sturgeon that can be used 1 to 2 years earlier than current methodologies.