Determination of sex and maturity in Acipenser stellatus by using ultrasonography

An important aspect in the management of endangered species is the determination of sex and maturity stages without killing the fish. Establishing accurate sex and maturity determination, in particular when external sexual dimorphism is not obvious or when external characters are not developed, has usually involved the use of either hormone radio-immunoassays or biopsy techniques. These methods are time- and labor-consuming as well as harmful to the fish. Therefore, it would be ecologically and economically important for caviar-producing countries to develop effective and reliable non-invasive methods for determination of sex and maturity in sturgeons. Ultrasonography examinations were performed to determine the sex and differences between mature and immature Acipenser stellatus. A total of 249 captured stellate sturgeons > 95 cm in length were examined using a linear transducer. Sex determination was carried out based on the differences in echogenicity ( brightness of tissues being displayed) and the morphology of ovaries and testes. Results of ultrasonography were confirmed at necropsy: 199 fish were females ( 63 mature and 136 immature) and 50 were males ( 29 mature and 21 immature). Ultrasonographic methods provided a 97.2% accuracy in sex determination. Gonads of immature males can be difficult to discern. The speed of examination was around 30 s or less per fish, depending on the stage of maturation.