Histological Characterization and Oocyte Development in Pearlspot, Etroplus suratensis (Bloch, 1790) From Vembanad Lake, Kerala, India

This study is the first to elucidate the oocyte growth pattern of Etroplus suratensis through detailed gonad histology. Ovary samples from different maturity stages were collected from October 2023 to September 2024 from cage culture systems installed in Vembanad Lake, Kumbalangi, Kerala, India. Ovary samples were processed for histology. Oocyte developmental stages were classified using histological markers, including nuclear morphology, follicular organization and ooplasmic staining characteristics, together with morphometric indices, including oocyte diameter, shape and nucleocytoplasmic index. Progressive changes in follicular structure, the emergence of cortical alveoli and shifts in ooplasmic staining distinguished the transition from primary to secondary oocyte growth. The simultaneous presence of oogonia, pre‐vitellogenic and vitellogenic oocytes within the same ovary, together with the occurrence of post‐ovulatory follicles and atretic oocytes, indicates continuous oocyte recruitment and multiple spawning events. A gradual decrease in the nucleocytoplasmic index across successive oocyte developmental stages indicates that increases in oocyte size are driven mainly by cytoplasmic growth rather than by nuclear enlargement. Atresia was most evident among post‐vitellogenic oocytes, while the prevalence of post‐ovulatory follicles indicates recent spawning. These findings support the classification of E. suratensis as an iteroparous batch spawner with asynchronous oocyte development and provide a histological framework relevant to reproductive assessment and broodstock management.