Mating behaviour of the orange mud crab, Scylla olivacea: The effect of sex ratio and stocking density on mating success

• The mating process of S. olivacea includes four phases (precopulation, molting, copulation and postcopulation) and lasted for 82.0 ± 10.8 h.
• Mating success was unaffected by sex ratio and inversely affected by stocking density.
• Cumulative mortality increased with increasing stocking density and unequal sex ratios.
• Postcopulatory guarding duration was shorter at higher female to male ratio and lower stocking density.

Mud crabs from the genus Scylla have high commercial value and are considered as one of the highly sought luxury seafood items. Thorough understanding about their biology and mating behaviour is vital in providing important information for a sustainable exploitation and future incorporation into the aquaculture industry. The mating process of S. olivacea lasted 82.0 ± 10.8 h was divided into four phases: precopulation, molting, copulation, and postcopulation. Courtship displays and fighting were shown by mature males while they were courting females. Precopulatory position lasted for 55.2 ± 10.8 h before the pairs disengaged for the female to molt. The molting process was 4.6 ± 0.3 h. Copulation (mean duration was 6.6 ± 0.5 h) occurred while the female’s exoskeleton was still soft. Postcopulatory guarding lasted for 13.6 ± 0.6 h. Separation of the mating pairs indicates the end of postcopulation phase. Mating success percentage was unaffected by sex ratio, but inversely affected by stocking density. Cumulative mortality increased with increasing stocking density and unequal sex ratios. Postcopulatory guarding duration was significantly shorter in treatment with 1 male:2 females ratio and treatment with the lowest stocking density (2 crabs m−2). We proposed rearing of mud crab broodstocks for mating purpose using sex ratio of 1 male:2 females and stocking density of 6 crabs m−2 to maximize output (successful mating pairs) while maintaining low mortality percentage and shorter postcopulatory guarding duration.