Sex and reproductive stage identification of sturgeon hybrids (Acipenser naccarii × Acipenser baerii) using different tools: ultrasounds, histology and sex steroids

Summary Sex and stage of gonad maturity in 6 year-old sturgeon hybrids (Acipenser naccarii female × Acipenser baerii male) were examined by means of ultrasonography, histology and sex steroid analyses during the reproductive season. Ultrasound images of gonads revealed male and female sturgeons at different stages of maturity, distinguished by gonad morphology and tissue echogenicity. Sexing and staging were found to be more difficult in immature fish, especially males, and ultrasounds were combined with sex steroids and histological analysis to confirm the sex and gonad developmental stage. Histology identified males and females at different developmental stages. Serum testosterone differed significantly between mature males and females (321 vs 15.4 ng ml−1) as well as 17β estradiol (0.4 vs 4.2 ng ml−1). High testosterone concentration was found also in immature sturgeon females. The male : female sex ratio was 1 : 1.5. Size was found to be significantly different between males (9.2 kg and 114.8 cm) and females (12.9 kg and 121.6 cm). Results indicate ultrasounds as a reliable, rapid and non invasive method to determine sex and maturity stages in hybrid sturgeon A. naccarii × A. baerii during the reproductive period, affording benefits to farmers for sex selection and breeding purposes. Further investigations are needed, in particular in immature individuals and outside the reproductive season, to identify sturgeon sex as early as possible.