Comparison of Catch Sizes and Reproductive Biology of Mud Crab Species of the Genus Scylla , Coexisting Populations in the Eastern Gulf of Thailand

Edible mud crabs (genus Scylla) showed a rapidly increasing demand over time. In the Eastern Gulf of Thailand, there are 3 Scylla species were reported and this study aims to understand the fisheries characteristic and life history of individual mud crab species, which occupying in the same area, focusing on catch size and reproductive biology. Comparisons on catch size and reproductive biology among the three species of the genus Scylla (Scylla paramamosain, Scylla olivacea and Scylla tranquebarica) were conducted in Trat Province fishing ground, Eastern Gulf of Thailand. Size spectra of the catch, measured by external carapace width (ECW), ranged from 68 – 155 mm, in which the differences were found both by in terms of species and sexes, so did the weight. All three mud crab species spawn all year round with two peaks i.e., firstly during February-March and secondly during June-November. Average fecundity of S. paramamosain, S. olivacea and S. tranquebarica was 2,116,514 (+790,649), 1,710,286 (+505,669) and 2,052,305 (+693,208) eggs/crab, respectively. The size at 50% maturity of females S. paramamosain, S. olivacea and S. tranquebarica were 111.67, 99.35 and 110.97 mm, respectively. The recommended minimum ECW size for female crab is set at 120 mm, to guarantee the sustaining of the resources, is suggested.