Ultrasonography in the reproductive management of the Brazilian sardine Sardinella brasiliensis

Abstract

Ultrasonography is a fast and non-invasive method that offers a promising alternative for sex identification and gonadal maturation assessment in fish. This technique is especially relevant to Brazilian sardine (Sardinella brasiliensis), a species of high commercial value whose small body makes traditional sexing methods unfeasible. Ultrasonography was applied to 55 individuals undergoing their first gonadal maturation. All fish were anesthetized for examination and subsequently euthanized for macroscopic evaluation to confirm sex and determine the maturation phase. These findings were supported by histological analysis, which confirmed the accuracy of the results. Ultrasonography using a multifrequency transducer (8–13 MHz) achieved 98% accuracy in sex identification, and 46 males and nine females were identified. Histological examination revealed 32 reproductively capable males (phase C) and 14 immature individuals (phase A), while all females were classified as phase C (ready for reproduction and spawning). Although ultrasonography proved effective for sex differentiation, it showed limitations in determining gonadal maturation phases. Further studies and the development of a specific protocol are required for accurate phase classification. Therefore, ultrasonography demonstrates great potential as a practical and effective tool in reproductive monitoring. This study is the first report of its application to the Brazilian sardine.