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±10.8h 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±10.8h before the pairs disengaged for the female to molt. The molting process was 4.6±0.3h. Copulation (mean duration was 6.6±0.5h) occurred while the female’s exoskeleton was still soft. Postcopulatory guarding lasted for 13.6±0.6h. 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

The size distribution, length–weight relationship and size at the onset of sexual maturity of the orange mud crab (Scylla olivacea) from four geographically distinct locations (Taiping, Setiu, Kota Marudu and Lundu) representing Malaysian waters were analysed and estimated. Scylla olivacea was found in the size range of 47–134 mm carapace width. Males were significantly smaller in size but heavier than females. Geographical variation in carapace width and body weight were significant, but no interaction was found between sexes and locations. As shown by the length–weight relationships of S. olivacea, the males exhibited positive growth allometry whereas the females exhibited negative growth allometry. Males mature physiologically prior to attaining morphometric sexual maturity. Females, however, achieve physiological and morphometric sexual maturity in synchrony. No significant variation was found in the estimates of size at the onset of sexual maturity of males and females among different locations. We recommend the use of the third right walking leg merus length and carapace width to estimate the size at the onset of sexual maturity (morphometric maturity) for S. olivacea. Data obtained in this study serve as important baseline data for future mud crab resource management in Malaysia and were used to recommend minimum landing sizes for S. olivacea in each respective location based on the largest size at the onset of sexual maturity estimates were suggested.

Adequate genetic information is essential for sustainable crustacean fisheries and aquaculture management. The commercially important orange mud crab, Scylla olivacea, is prevalent in Southeast Asia region and is highly sought after. Although it is a suitable aquaculture candidate, full domestication of this species is hampered by the lack of knowledge about the sexual maturation process and the molecular mechanisms behind it, especially in males. To date, data on its whole genome is yet to be reported for S. olivacea. The available transcriptome data published previously on this species focus primarily on females and the role of central nervous system in reproductive development. De novo transcriptome sequencing for the testes of S. olivacea from immature, maturing and mature stages were performed. A total of approximately 144 million high-quality reads were generated and de novo assembled into 160,569 transcripts with a total length of 142.2 Mb. Approximately 15–23% of the total assembled transcripts were annotated when compared to public protein sequence databases (i.e. UniProt database, Interpro database, Pfam database and Drosophila melanogaster protein database), and GO-categorised with GO Ontology terms. A total of 156,181 high-quality Single-Nucleotide Polymorphisms (SNPs) were mined from the transcriptome data of present study. Transcriptome comparison among the testes of different maturation stages revealed one gene (beta crystallin like gene) with the most significant differential expression—up-regulated in immature stage and down-regulated in maturing and mature stages. This was further validated by qRT-PCR. In conclusion, a comprehensive transcriptome of the testis of orange mud crabs from different maturation stages were obtained. This report provides an invaluable resource for enhancing our understanding of this species’ genome structure and biology, as expressed and controlled by their gonads.