Histological-based characterization of ovarian developmental stages in blue crab (Callinectes sapidus) within the spawning season in the central western Adriatic Sea

The Atlantic blue crab (Callinectes sapidus Rathbun, 1896) is a euryhaline and eurythermal species native to the Atlantic coasts of the Americas. Although its widespread distribution across the Mediterranean basin is well documented, information on its reproductive patterns remains limited. This study focused on the combination of both macroscopic and histologic characterization of ovarian developmental stages in female blue crabs along the north-central Italian Adriatic coast, within the spawning period. Samples were collected off the coast of Ancona, in collaboration with local fishermen, between September and November 2023. For each specimen, sex and biometric parameters were recorded to determine the sex ratio, while size distribution and gonadosomatic index (GSI) were calculated for female specimens. Ovary samples and eggs sponge were collected to determine the ovarian developmental stage and fecundity respectively. Results showed females as the dominant sex throughout the sampling period, with males being extremely rare. The collapse of female catches in early November, alongside the consistent presence of ovigerous females and the strong female-biased sex ratio, identified this area as a spawning ground. These findings align with reproductive patterns observed in the species' native range and other Mediterranean areas. Moreover, GSI values and fecundity indexes associated with macroscopic and histological examination of ovarian stages suggested that the end of the reproductive season corresponded to mid-November.