Assessment of Sex, Gonad Volume, and Reproductive Maturation Status of the Indian Shad, Tenualosa ilisha, Using Ultrasonic Imaging: A Rapid and Non-Invasive Tool

To determine sex and maturity stages accurately without any physical injury and stress, especially for sensitive and high-value fish species, employing a noninvasive ultrasound imaging technique could be a desirable approach. The ultrasound imaging method as a powerful eco-friendly tool was established to determine sex, gonad volume, gonadosomatic index (GSI), and reproductive stages in the Indian shad, hilsa (Tenualosa ilisha). About 30 hilsa (15 males and 15 females) of different maturity stages were collected from the river Ganga round the year using gill nets. The ultrasound sonography (USG) was then employed in hilsa to determine the computed GSI. The fresh gonad volume of hilsa was determined using a water displacement method to ascertain actual GSI values. There was no significant difference between the calculated, real, and actual GSIs (P > 0.05) in both males and females. The validation of the precise maturity stages of ultrasound images of the gonad by the histological architecture indicated that USG images of the hilsa gonad depicted exact stages of maturity in both sexes except for stages I and II in males. The sex of the fish was accurately ascertained using ovarian ultrasound scanning for all the specimens. The calculated USG-based ovarian volume was positively correlated (R² = 0.97) with the actual and real ovarian volumes. The noninvasive and reliable ultrasonography technique was found to be an accurate and valid tool to track gender and gonadal development and predict the spawning periodicity in hilsa.