The progression of oocyte development and patterns of oocyte recruitment are key indicators of reproductive strategy in fishes. The present study examines, for the first time, the fecundity strategy of cage‐reared Etroplus suratensis in Vembanad Lake using four indicators: (a) the oocyte size frequency distribution across ovarian reproductive phases and sampling months; (b) the proportional distribution of the oocyte developmental stages across each ovarian reproductive phase; (c) seasonal trends in the mean diameter of advanced vitellogenic oocytes; and (d) the seasonal incidence of oocyte atresia. The samples were collected monthly from October 2023 to September 2024, with 202 ovaries categorized by macroscopic observation into various ovarian reproductive phases. From these, 54 ovaries representing all ovarian reproductive phases were selected for histological examination and image analysis techniques. Histological examination identified seven distinct oocyte development stages in addition to postovulatory follicles and atretic oocytes. The oocyte size distribution revealed asynchronous oocyte development and continuous secondary growth, with no distinct separation between previtellogenic and vitellogenic oocytes. Gaussian mixture model analysis identified five distinct oocyte size clusters corresponding to successive developmental stages, confirming the presence of multiple cohorts. Logistic regression showed that the size at which 50% of oocytes recruited into vitellogenesis decreased across spawning‐capable phases, reflecting rapid oocyte recruitment during repeated spawning events. A seasonal decline in the mean diameter of advanced vitellogenic oocytes was evident during the spawning season, indicating the continuous replenishment of oocytes within the advanced vitellogenic pool. A relatively stable proportion of cortical alveolar and vitellogenic oocytes during the spawning season suggests continuous recruitment of oocytes into the vitellogenic pool through de novo vitellogenesis . Furthermore, an increased occurrence of atretic oocytes was noticeable towards the end of the spawning season (i.e., August to October), reflecting a common strategy in species with indeterminate fecundity to reabsorb surplus oocytes. These findings demonstrate that E. suratensis exhibits asynchronous oocyte development, continuous oocyte recruitment and batch spawning with an indeterminate fecundity pattern. This reproductive strategy observed supports prolonged spawning activity and provides important implications for brood stock management and seed production in estuarine cage culture systems.
Hussain et al. (Thu,) studied this question.