First Gonadal Stages of Bonito, Sarda chiliensis (Perciformes: Scombridae) on the Pacific Coast of Northern Chile

<ns3:p> Background The study of the reproductive biology of pelagic fish species, such as <ns3:bold> <ns3:italic>Sarda chiliensis</ns3:italic> </ns3:bold> (Bonito), is essential for effective fisheries management and aquaculture development. Overfishing has significantly impacted the population of pelagic fish species, making it crucial to understand their reproductive cycles, including maturity stages and spawning periods, to ensure sustainable exploitation. Methods This study provides the first histological characterization of the early gonadal stages of <ns3:bold> <ns3:italic>Sarda chiliensis</ns3:italic> </ns3:bold> from northern Chile. A total of 444 specimens were collected from artisanal fisheries between December 2013 and June 2014. Gonadal maturity stages were identified using histological techniques, and a range of microscopic stains (Hematoxylin-Eosin, Van Gieson, and Periodic Acid–Schiff ) were employed to examine the cellular structure of the gonads. Results Two key gonadal stages—inactive and previtellogenic—were identified in females, while males exhibited both immature and mature stages. Histological observations revealed distinct characteristics of early gonadal development, including primary oocytes and spermatogonia, with evidence of early vitellogenesis in females. No mature females were observed, and the smallest mature female recorded was 48.5 cm in total length. The gonadosomatic index (GSI) exhibited temporal fluctuations, with a peak observed in February. Conclusions This study provides vital histological data on the early gonadal stages of <ns3:bold> <ns3:italic>Sarda chiliensis</ns3:italic> </ns3:bold> from northern Chile, offering a baseline for future reproductive studies and aquaculture initiatives. The absence of mature females in the sample highlights the need for broader temporal and spatial sampling to fully characterize the reproductive cycle. These findings are crucial for developing sustainable fisheries management strategies and improving broodstock conditioning for aquaculture. </ns3:p>