Reproductive biology of mangrove clams Geloina expansa (Mousson, 1849) from mangrove at Kendari Bay, Southeast Sulawesi, Indonesia

ABSTRACT Mangrove clams are found in the soft substrates of the mangrove forest, where they reproductively adjust to the conditions in the aquatic environment. This study aimed to determine the reproductive biology pattern, such as sex ratio, gonad maturity level, gonadosomatic index, fecundity and size of the first maturity of mangrove clams. The samples included 80 ind./month collected manually from the mangrove ecosystem for one year. The reproductive biology patterns were calculated using standard formulas, each analysed using the χ2 test, semi-quantitative descriptive evaluation and non-linear regression. The results showed that more males than females were collected, accounting for 80.0–96.5% and 3.4–20.0%, respectively. Furthermore, both sexes’ gonad maturity developments coincided. The mangrove clam’s mature gonads are discoverable all year by observing the gonadosomatic index IV and spawning monthly occurrence. Their maturity peaked (levels III and IV) in February–April, indicated by a high index value ranging from 3.9–18.2 and 4.3–21.9 for the male and female mangrove shells, respectively. The male clams also had smaller sizes at maturity than females at 3.0 and 5.2 cm lengths, respectively. The food (organic sediment) availability was an essential environmental parameter in developing gonadal maturity.