A nuanced understanding of the reproductive dynamics, growth trajectories, and environmental interactions of the Indian backwater oyster ( Crassostrea madrasensis ) is indispensable for advancing knowledge for ensuring population sustainability, tropical mariculture, and guiding conservation strategies in monsoon-driven tropical ecosystems. Therefore, this study undertook an integrated, year-long (May 2023–April 2024) investigation of reproductive biology, biometric growth patterns, and trophic relationships of C. madrasensis from the Moheshkhali Channel, a dynamic marine-influenced habitat along the southeast coast of the Bay of Bengal, Bangladesh, employing a multivariate analytical framework. Biometric assessments revealed consistent negative allometric growth, indicating preferential energetic allocation to shell accretion over somatic tissue development, thereby reflecting adaptive morphological plasticity in response to local environmental pressures. Histological analyses identified two distinct spawning peaks during the pre-monsoon (April–June) and post-monsoon (October–December) periods, corroborated by elevated condition indices (CI) and presumptive gonadosomatic indices (P.GSI). Seasonal fluctuations in sex ratios demonstrated a flexible reproductive strategy, characterized by female predominance during periods of heightened primary productivity and the occurrence of transient hermaphroditism during transitional months. Multivariate analyses (PCA and CVA) revealed strong seasonal coupling among reproductive stages, plankton ingestion patterns, and key environmental drivers, including temperature, salinity, dissolved oxygen, and nutrient availability. Planktonic diet composition exhibited pronounced seasonal shifts aligned with reproductive cycles, underscoring adaptive nutritional adjustments that support gametogenesis. The pre-monsoon reproductive phase appeared to rely primarily on endogenous energy reserves, whereas post-monsoon spawning was closely synchronized with peaks in phytoplankton abundance and nutrient influx, suggesting opportunistic utilization of exogenous energy inputs. Collectively, these findings advance ecological understanding of wild populations of C. madrasensis , offering vital baseline knowledge to guide conservation and sustainable utilization for maintaining natural oyster stocks and adaptive mariculture strategies in monsoon-influenced tropical estuarine environments. • This study examines the adaptive reproductive phenology and environmental synchrony of C. madrasensis. • The reproductive cycle is flexible, with female predominance and transient hermaphroditism during transitional months. • Two spawning peaks observed during pre- (April–June) and post-monsoon (October–December) seasons in C. madrasensis. • Seasonal coupling links reproductive stages with plankton ingestion and key environmental drivers. • Pre-monsoon reproduction indicates energy storage (conservative) strategies under resource-limited conditions. • Post-monsoon spawning is an externally fueled (opportunistic) synchronized with nutrient enrichment and high phytoplankton ingestion.
Ferdous et al. (Wed,) studied this question.