Gender and gonadal maturity stage identification of captive Chinese sturgeon, Acipenser sinensis, using ultrasound imagery and sex steroids.

•Gonadal maturation of the critically endangered Chinese sturgeon in captive.•Successful sex and maturity stages determination with ultrasonic imaging.•Maturity stages subdivided with quantitative parameters in ultrasonic images.•Changes of sex steroids levels at different maturity stages.•Accuracy of the sexing and staging with ultrasound imagery and sex steroids.