Age Structure and Growth Responses of the Pearl Oyster (Pinctada radiata) Under Contrasting Salinity Regimes in Bahrain Waters, Arabian Gulf

Understanding age and growth in marine bivalves is essential for interpreting population dynamics and environmental responses. The analysis of sclerochronological growth increments within internal shell layers provides a reliable approach for reconstructing age and growth history and preserves long-term records of environmental variability and stress. This study presents the first assessment of age structure and growth history of the pearl oyster Pinctada radiata in Bahrain waters using shell growth-line analysis. Pearl oysters from two contrasting salinity regimes in Bahrain waters, the Northern Area (~40‰) and the hypersaline Western Coast (~55‰), were examined using acetate peel replicas and internal shell growth-line analysis. Age determination was conducted from shell cross-sections, and growth patterns were evaluated through morphometric analysis and von Bertalanffy growth modelling. Oysters from the Northern Area attained larger shell sizes and exhibited estimated life spans of up to 5–6 years, whereas hypersaline populations displayed reduced life spans (3–4 years), thinner shells, and lower asymptotic growth despite rapid early development. A strong correlation between shell height and umbo height supported the reliability of internal growth increments as age proxies. These findings suggest that pearl oysters inhabiting naturally hypersaline habitats may exhibit a dwarf-like growth pattern and reduced life span associated with persistent hypersalinity. The results improve understanding of growth responses and physiological limits of P. radiata under naturally hypersaline conditions in the Arabian Gulf.