Spawning season estimation for bullet tuna (<i>Auxis rochei</i> Risso, 1810) in southern waters of Bali: A postovulatory follicles - based approach

Bullet tuna is a crucial neritic tuna species in Indonesia that plays a significant role in small-scale and commercial fisheries. Regulation of seasonal fishing is an example of fishery resource management to prevent negative impacts on fishery resources due to fishing pressure. Postovulatory follicles (POFs) are a potential characteristic for determining spawning season in adult fish that have already spawned. The objective of this study was to determine the spawning season of bullet tuna ( Auxis rochei ) in the presence of POFs. This study employed purposive stratified sampling techniques, which were obtained from gill net fishing boats operating in the Kedonganan Fish Landing Base, Bali. Sampling was conducted from June to November 2021, and 151 ovaries were collected including the morphometric such as fork length (cm FL). Fresh ovary samples were fixed for histological analysis using the paraffin method and Harris-Hematoxylin and Eosin staining. The spawning season was determined by the presence of POFs at the spawning gonad development stage in the length range of 22-32 cm FL, indicating that peak spawning occurred in August. These findings can be used as a reference for formulating the management of bullet tuna in Bali.