Reproductive cycle of the oyster Crassostrea (Magallana) saidii (Wong and Sigwart, 2021) from Southeast Asia

Crassostrea (Magallana) saidii has been commercially ranched in Malaysia and consumed for more than 160 years, but it was only recently identified as a new species to science. This study was conducted to evaluate the reproductive phenology of C. (M.) saidii. Samples of 30 individual oysters were taken monthly for 15 months from the sole population at Sungai Muar estuary in Johor, Malaysia. The sex ratio was 1:1.64 (male:female) for all examined specimens, with female numbers significantly higher. Hermaphrodism was detected in 1.56% of all samples. Spawning peaks in April (2019) and November (2018 and 2019), and were positively associated with the increased rainfall upstream. Gametogenesis occurred throughout the research period with temporal variations. The highest values of maturity index (MI) were recorded in March, August and October 2019, when most oysters were in matured and maturing stages. Condition index (CI) ranged from 31.90 ± 1.25 (April 2019) to 70.03 ± 3.23 (October 2019), exhibiting two peaks (March and October 2019) and subsequently reduced in CI indicating spawning consistency with histological observations. Anthropogenic stressors such as heavy sedimentation and inland development are threatening the survival of this species. The understanding of their reproductive biology is essential to ensure the survival and sustainability of C. (M.) saidii fishery.

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