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The objective of this study was to test existing ultrasound technology for use in early sex identification in beluga sturgeon (3-years-old fish) while including some methodological adjustments. Eighty cultured Beluga sturgeons aged 3 years underwent ultrasonographic examination using a high frequency transducer for sex determination. Sexing of the sturgeons was based on the shape and echogenicity (brightness) of the gonad and surrounding fat tissue in sonographic scans. Accuracy of ultrasound sex determinations were confirmed through directly inspecting the gonads by a small incision in the right or left ventral body wall. Females were identified with 96.7% accuracy (n = 31) and males with 97.9% accuracy (n = 49). Overall accuracy of sex determination using ultrasonography was 97.5%. Using high frequency transducer and transverse scanning just over the swim bladder in 3-year-old beluga may have been contributed in high accuracy sex detection. These technically improvements may be considered an advantage for beluga culture because this fish matures extremely late compared to other sturgeon species.

There is a significant lack of data for the biological parameters of beluga or great sturgeon, the largest fish in the Caspian Sea. The age, growth and fisheries indices for the stock status of beluga was investigated in the south Caspian Basin of Iran between 1990 and 2011. Fork lengths ranged between 113-420 cm and weights from 8.0 to 725.0 kg. The growth parameters were L∞ = 440 cm, K = 0.027 year−1, t0 = − 5.8 years. The age at first capture (tc) was 13.1 years. The long-term age composition data showed age up to 63 years, and the ages 12-19 years comprised 76.7% of the total catch. The generation length was 33 years. The values of “KF” were close to 1 or >1, indicating that beluga sturgeon is in a favorable condition in the southern Caspian Sea. The length distribution showed that 24.2% of the catch is comprised of juveniles. Based on the age structure and age at first maturity, recruitment and growth overfishing occurred in beluga stocks. Therefore, increased length or age at first capture in future fishery policies should be implemented. The mega-spawners represented 4.4% of the fish captured and revealed an unhealthy population structure.