Genus Scylla Research Articles

Identification of Indian Mangrove Mud Crab GenusScyllaspp. (Brachyura: Portunidae) using Rapd and Pcr-Rflp Markers

Identification of commonly available Indian mud crabs of the genus Scylla was carried out using RAPD and PCR-RFLP to resolve the taxonomic ambiguity of the genus. Samples were collected from western, eastern, and Andaman coastal waters of India. A total of 16 potential species-specific RAPD markers were identified from 179 individuals using 4 arbitrary primers (OPA2, OPA14, UBC122, and UBC456). Three PCR-RFLP markers were developed that could be used to confirm taxonomic status of Indian mud crab species. The species-specific RAPD markers and the digestion pattern of PCR-RFLP analysis indicate conclusively that only 2 species of mud crabs (Scylla serrata and Scylla olivacea) are commonly present in Indian coastal waters.

Morphological Description of Pedunculate Barnacle Octolasmis angulata (Aurivillius, 1894) on Wild Mud Crab Genus Scylla from Setiu Wetland, Terengganu Coastal Water, Malaysia

Morphological Description of Pedunculate Barnacle Octolasmis angulata (Aurivillius, 1894) on Wild Mud Crab Genus Scylla from Setiu Wetland, Terengganu Coastal Water, Malaysia

Molecular Markers Reveal Only Two Mud Crab Species of Genus Scylla (Brachyura: Portunidae) in Indian Coastal Waters

The taxonomic ambiguity of the Indian mud crab (genus Scylla de Hann 1833) is still a cause of concern as several papers have been published with misleading identification. This is the first attempt to resolve the taxonomic uncertainty of the mud crab commonly available in Indian coastal waters using molecular genetic markers (ITS-1 and sequencing of COI gene) combined with traditional morphometry. Additionally, we developed a PCR method by which Indian mud crab species can be identified rapidly and effectively. The results clearly indicate that the green morph of the Indian mud crab is Scylla serrata and the brown morph is S. olivacea. The S. serrata commonly mentioned in the literature from India is S. olivacea; the S. tranquebarica noted by many Indian researchers should belong to S. serrata. Caution should be taken when interpreting or implementing the biological, molecular, and aquaculture data in the literature.

DNA sequence information resolves taxonomic ambiguity of the common mud crab species (Genus Scylla) in Indian waters

For several years, mud crabs of genus Scylla have been misidentified owing to their high morphological plasticity and the absence of distinct morphological diagnostic characters. The taxonomic confusion of genus Scylla de Haan is considered to be a primary constraint to the development of aquaculture. Although genus Scylla was revised using morphological and genetic characteristics, taxonomy of Scylla species occurring in India is still not clear. In this study, partial sequences of two mitochondrial genes, 16S rRNA and CO1 (Cytochrome C oxidase subunit I) in populations of Scylla spp. obtained from eleven locations along the Indian coast were used to differentiate and resolve taxonomical ambiguity of the mud crab species in India. The sequences were compared with previously published sequences of Scylla spp. Both trees generated based on 16S rRNA and CO1 indicated that all S. tranquebarica morphotypes obtained during this study and S. tranquebarica sequences submitted previously from Indian waters reciprocally monophyletic with reference sequence of S. serrata. Both sequence data and morphological characters revealed that the species S. serrata (Forskal) is the most abundant followed by S. olivacea. Further, the 16S rRNA and COI haplotypes of Indian S. tranquebarica obtained in the study significantly differed with the known S. tranquebarica by 6.7% and 10.6% respectively whereas it differed with known S. serrata by 0.0–0.7% only, a difference that was not statistically significant. From these studies it is clear that “S. tranquebarica” commonly reported from India should be S. serrata (Forskal).

Species composition, reproduction, and body size of mud crabs, Scylla spp., caught in Urado Bay, Japan

Species composition, reproduction and body size of mud crabs, genus Scylla de Haan, 1833, were investigated using gill nets from October 2008 to October 2009 in Urado Bay, Japan. Three mud crab species were identified in the area, with S. paramamosain Estampador, 1949 being the dominant species (74% of the catch), followed by S. serrata (Forskal, 1775) (23%) and S. olivacea (Herbst, 1796) (3%). We found temporal changes in species composition with abundances of S. serrata increasing towards the summer season. Ovigerous females of S. paramamosain and S. olivacea occur between January and October, peaking in the warm (May-July) and rainy (June-July) seasons, but we found no berried females of S. serrata. The female-biased sex ratios of S. paramamosain and S. serrata, and the larger body size of females during the period from autumn (November) to early spring (April), suggest that large gravid females may have migrated offshore before the spawning season. The mean body size of females and males of S. paramamosain and S. serrata tended to increase and the mating activity was high between May and October, showing the moulting and growth season.

Molecular identification of genus Scylla (Decapoda: Portunidae) based on DNA barcoding and polymerase chain reaction

In this study, we first examined the utility of COI sequences as DNA barcoding for identification of genus Scylla, which includes four species: Scylla paramamosain, Scylla serrata, Scylla tranquebarica and Scylla olivacea. The mean intraspecific Kimura 2-parameter distances were 0.003 for S. paramamosain, 0.014 for S. serrata, 0.017 for S. olivacea and 0.006 for S. tranquebarica. The interspecific K2P distances were higher than the intraspecific distances: the minimum interspecific distance (0.092) was between S. paramamosain and S. tranquebarica while the maximum interspecific distance (0.196) was between S. paramamosain and S. olivacea. No overlap was found between intraspecific and interspecific distances, suggesting the existence of a distinct barcoding gap. The maximum-likelihood (ML) phylogenetic tree consisted of four distinct clusters, each containing individuals from one species only. Furthermore, a molecular species identification method was developed successfully, by which these four species could be identified rapidly and effectively from each other though a PCR reaction.

Biological information and population features of mud crab, genus Scylla from mangrove areas of Sarawak, Malaysia

This study was conducted to determine the size at maturity, size at mating, sex ratio and carapace width (CW) to body weight (BW) ratio of the most abundant mud crab species sampled in mangrove areas of Sarawak, Malaysia. Additionally, the taxonomic statuses of Scylla spp. mud crabs from this area were assessed. A total of 14,000 mud crabs representing different sizes, sexes and species were examined to determine taxonomic status and sex ratio for each. In addition, 2000 mud crabs were randomly measured to determine the CW–BW relationship. A total of 1724 female crabs and 1230 male crabs of various sizes were randomly sampled to determine the size at maturity and size at mating. The results indicate that the size at maturity of female S. olivacea and S. tranquebarica were 8.6 cm CW and 9.2 cm CW, respectively. The size at maturity of male crabs is very similar but could not be confirmed because all S. olivacea and S. tranquebarica individuals sampled were already mature. Size at mating for female and male S. olivacea was 9.6 cm CW and 11.3 cm CW, respectively. For female and male S. tranquebarica, size at mating was 10.8 cm CW and 13.1 cm CW, respectively. S. olivacea was the most common mud crab species in this area, comprising 77.64% of total species, followed by S. tranquebarica (21.91%) and S. paramamosain (0.45%). S. serrata were not found during this study. The sex ratios (male:female) for S. olivacea and S. tranquebarica were 1:0.89 and 1:0.75, respectively. The BW increment rate for male crabs of S. olivacea and S. tranquebarica were higher relative to that for female crabs. The CW–BW relationship shows that S. tranquebarica was heavier than S. olivacea. The study also indicates that the selective fishing of mature crabs at a particular site where S. olivacea and S. tranquebarica occur together can cause negative impacts on the populations of these species by affecting size at maturity, size at mating and population dynamics. The biological information and population features from this study can be used in sustainable management and exploitation of mud crab resources in Malaysian coastal waters and the South China Sea.

Mud crab susceptibility to disease from white spot syndrome virus is species-dependent

BackgroundBased on a report for one species (Scylla serrata), it is widely believed that mud crabs are relatively resistant to disease caused by white spot syndrome virus (WSSV). We tested this hypothesis by determining the degree of susceptibility in two species of mud crabs, Scylla olivacea and Scylla paramamosain, both of which were identified by mitochondrial 16 S ribosomal gene analysis. We compared single-dose and serial-dose WSSV challenges on S. olivacea and S. paramamosain.FindingsIn a preliminary test using S. olivacea alone, a dose of 1 × 106 WSSV copies/g gave 100% mortality within 7 days. In a subsequent test, 17 S. olivacea and 13 S. paramamosain were divided into test and control groups for challenge with WSSV at 5 incremental, biweekly doses starting from 1 × 104 and ending at 5 × 106 copies/g. For 11 S. olivacea challenged, 3 specimens died at doses between 1 × 105 and 5 × 105 copies/g and none died for 2 weeks after the subsequent dose (1 × 106 copies/g) that was lethal within 7 days in the preliminary test. However, after the final challenge on day 56 (5 × 106 copies/g), the remaining 7 of 11 S. olivacea (63.64%) died within 2 weeks. There was no mortality in the buffer-injected control crabs. For 9 S. paramamosain challenged in the same way, 5 (55.56%) died after challenge doses between 1 × 104 and 5 × 105 copies/g, and none died for 2 weeks after the challenge dose of 1 × 106 copies/g. After the final challenge (5 × 106 copies/g) on day 56, no S. paramamosain died during 2 weeks after the challenge, and 2 of 9 WSSV-infected S. paramamosain (22.22%) remained alive together with the control crabs until the end of the test on day 106. Viral loads in these survivors were low when compared to those in the moribund crabs.ConclusionsS. olivacea and S. paramamosain show wide variation in response to challenge with WSSV. S. olivacea and S. paramamosain are susceptible to white spot disease, and S. olivacea is more susceptible than S. paramamosain. Based on our single-challenge and serial challenge results, and on previous published work showing that S. serrata is relatively unaffected by WSSV infection, we propose that susceptibility to white spot disease in the genus Scylla is species-dependent and may also be dose-history dependent. In practical terms for shrimp farmers, it means that S. olivacea and S. paramamosain may pose less threat as WSSV carriers than S. serrata. For crab farmers, our results suggest that rearing of S. serrata would be a better choice than S. paramamosain or S. olivacea in terms of avoiding losses from seasonal outbreaks of white spot disease.

Genetic Relationship between the Genus Scylla and Four Portunids

Genetic Relationship between the Genus Scylla and Four Portunids

Discrimination using the color variation of chela in the mud crab genus Scylla in Japan

Discrimination using the color variation of chela in the mud crab genus Scylla in Japan

The benefits of species-based management of sympatric mud crabs migrating to a common fishing ground

AbstractJirapunpipat, K., Yokota, M., and Watanabe, S. 2009. The benefits of species-based management of sympatric mud crabs migrating to a common fishing ground. – ICES Journal of Marine Science, 66: 470–477. The issue of effective fisheries management in sympatric species of mud crab of the genus Scylla on a local fishing ground is examined. A simple model is developed that allows the calculation of yield-per-recruit (YPR) based on deterministic body growth of two ideal coexisting crab species and their survival after migration to a fishing ground under two different fishing strategies. First, the basic strategy is traditional species-aggregated fishing, which does not distinguish the start of fishing and fishing effort among species. Therefore, the species-aggregated fishing strategy can be treated as if only a single species existed despite the coexistence of separate crab species on the fishing ground. This is in common use, because species discrimination of mud crabs is difficult. Second, an alternative strategy of species-based fishing is proposed, in which two fishing parameters are controlled depending on the demographic variables of each species. The application of the model to several combinations of individual growth rate (k) and natural mortality (M) between two species demonstrates that YPR for species-based management is larger than for species-aggregated fishing. Numerical simulations suggest that species-based fishing is advantageous even when fishing is controlled for only one species and the parameters of the other species are unknown. These findings could be applied not only to the effective management of sympatric mud crabs, but also to other overlapping species.

The Occurrence and Distribution of Stalked Barnacles of the Genus Octolasmis on the Gills of Mud or Mangrove Crab, Genus Scylla

[Several specimens of the mud crab, Scylla cf. tranquebarica (Fabricius, 1798), were examined for the presence of stalked barnacles on the gills. Eighty-five percent of the crabs, for the size group 50 to 108 mm carapace width, were found infested with stalked barnacles. In all crabs, the barnacles were found attached to the inner (hypobranchial) surface of the gill with the exception of a single crab in which the barnacles were also found attached to the outer (epibranchial) surface of the gill. The stalked barnacles were identified as Octolasmis cor (Aurivillius, 1892) and O. angulata (Aurivillius, 1894), and our size-frequency data support the view that they are indeed distinct species. Their distribution on various parts of the gills, i.e., proximal, medial, or distal, was noted. Most of the barnacles were found attached to the medial part of the gill (O. cor 55%; O. angulata 57%), followed by the proximal part (O. cor 31%; O. angulata 38%), and the distal part (O. cor 14%; O. angulata 5%). Gill number 7 bore the maximum number of O. cor (33%) found, whereas gill number 4 harboured the maximum number of O. angulata (30.2%). Divers specimens du crabe Scylla cf. tranquebarica (Fabricius, 1798), ont ete examines pour rechercher la presence de bernacles pedoncules sur les branchies. Un total de 85% des crabes, pour le groupe de taille de 50 a 108 mm de largeur de carapace, ont ete trouves infestes par des bernacles pedoncules. Dans tous les crabes, les bernacles ont ete trouves accroches a la face interne de la branchie (hypobranchie) a l'exception d'un seul crabe chez lequel les bernacles ont ete trouves sur la surface externe (epibranchie) de la branchie. Les bernacles ont ete identifies comme Octolasmis cor (Aurivillius, 1892) et O. angulata (Aurivillius, 1894) et nos observations sur la distribution des tailles soutiennent l'hypothese qu'elles sont vraiment des especes separees. Leur distribution sur les differentes parties des branchies, i. e., proximal, median ou distal ont ete notees. La plus part des bernacles ont ete trouves accroches dans la partie mediane de la branchie (O. cor 55%; O. angulata 57%), suivie par la partie proximale (O. cor 31%; O. angulata 38%), et la partie distale (O. cor 14%; O. angulata 5%). La branchie 7 porte le nombre maximum de O. cor (33%) trouves, alors que la branchie 4 accueille un maximum de O. angulata (30.2%)., Several specimens of the mud crab, Scylla cf. tranquebarica (Fabricius, 1798), were examined for the presence of stalked barnacles on the gills. Eighty-five percent of the crabs, for the size group 50 to 108 mm carapace width, were found infested with stalked barnacles. In all crabs, the barnacles were found attached to the inner (hypobranchial) surface of the gill with the exception of a single crab in which the barnacles were also found attached to the outer (epibranchial) surface of the gill. The stalked barnacles were identified as Octolasmis cor (Aurivillius, 1892) and O. angulata (Aurivillius, 1894), and our size-frequency data support the view that they are indeed distinct species. Their distribution on various parts of the gills, i.e., proximal, medial, or distal, was noted. Most of the barnacles were found attached to the medial part of the gill (O. cor 55%; O. angulata 57%), followed by the proximal part (O. cor 31%; O. angulata 38%), and the distal part (O. cor 14%; O. angulata 5%). Gill number 7 bore the maximum number of O. cor (33%) found, whereas gill number 4 harboured the maximum number of O. angulata (30.2%). Divers specimens du crabe Scylla cf. tranquebarica (Fabricius, 1798), ont ete examines pour rechercher la presence de bernacles pedoncules sur les branchies. Un total de 85% des crabes, pour le groupe de taille de 50 a 108 mm de largeur de carapace, ont ete trouves infestes par des bernacles pedoncules. Dans tous les crabes, les bernacles ont ete trouves accroches a la face interne de la branchie (hypobranchie) a l'exception d'un seul crabe chez lequel les bernacles ont ete trouves sur la surface externe (epibranchie) de la branchie. Les bernacles ont ete identifies comme Octolasmis cor (Aurivillius, 1892) et O. angulata (Aurivillius, 1894) et nos observations sur la distribution des tailles soutiennent l'hypothese qu'elles sont vraiment des especes separees. Leur distribution sur les differentes parties des branchies, i. e., proximal, median ou distal ont ete notees. La plus part des bernacles ont ete trouves accroches dans la partie mediane de la branchie (O. cor 55%; O. angulata 57%), suivie par la partie proximale (O. cor 31%; O. angulata 38%), et la partie distale (O. cor 14%; O. angulata 5%). La branchie 7 porte le nombre maximum de O. cor (33%) trouves, alors que la branchie 4 accueille un maximum de O. angulata (30.2%).]

Population ecology of the mud crab Scylla paramamosain (Estampador) in an estuarine mangrove system; a mark-recapture study

Mud crabs of the genus Scylla are commercially important mangrove residents that are extensively fished throughout their range in the Indo-West Pacific. Despite this high level of exploitation very little is known about the population dynamics of any of the Scylla species. The present study concentrated on an exploited population of Scyllaparamamosain in a natural estuarine mangrove on Can Coc Island in the mouth of the Hau River, Mekong Delta, Vietnam. A total of 6,114 juvenile crabs captured on the seaward mangrove fringe were internally tagged by injection of coded microwire tags and released over a period of 29 days. Recaptures were monitored over the following 144 days. There was little migratory movement within the estuary; of 285 recaptured crabs, 93% were recovered within the island mangrove study area and only two individuals were recovered from mangroves lining the opposite mainland riverbanks. A von Bertalanffy growth function was fitted to growth increment data from recaptured crabs, with Lmax = 150 mm to derive a growth constant, k = 2.39 year−1. The theoretical age at which carapace width is zero (t0) was derived from known size at recruitment at instar 1, giving a value of −0.0095 years. Previous studies of the same population have shown that female S. paramamosain reach maturity at a mean size of 102 mm carapace width. The present study indicates that they attain this size at around 160 days from first settlement in the mangrove fringe. Abundance of juvenile crabs in the study area was estimated by the Petersen method as 1,101,500 (95% CI 4,17,300–1,785,800, representing 1,102 crabs ha−1 of mangrove. Estimation of mortality from tag returns and from the age-catch curves during a period of constant recruitment were comparable (Z = 1.11 and 1.04 month−1, respectively). Fishing only accounted for 14% of total mortality, suggesting that at the time exploitation was not at a critical level despite the apparent high level of fishing activity.

Scylla paramamosain (Estampador) the most common mud crab (Genus Scylla) in China: evidence from mtDNA

Scylla paramamosain (Estampador) the most common mud crab (Genus Scylla) in China: evidence from mtDNA

A Natural Hybrid Mud Crab (Decapoda, Portunidae) from Japan

Abstract A presumed hybrid mud crab of the genus Scylla was examined. The presumed hybrid could not be easily separated morphologically from the three Japanese Scylla species, S. serrata, S. paramamosain, and S. olivacea. An analysis of the first internal transcribed spacer (ITS-1) of the nuclear DNA revealed that the hybrid carried genomic DNA from both S. serrata and S. olivacea. Analysis of the maternally inherited 16S rDNA of the mitochondrial DNA demonstrated that the presumed hybrid carried S. olivacea mtDNA. Based on these results, we conclude that the examined animal is indeed the hybrid offspring of a female S. olivacea and a male S. serrata. The degree of genetic isolation among these species, and the possible causes of hybridization are discussed.

Identification of four mud crab species (genusScylla) using ITS-1 and 16S rDNA markers

The first internal transcribed spacer (ITS-1) of nuclear ribosomal DNA and mitochondrial DNA 16S rRNA were amplified by Polymerase chain reaction (PCR) using genomic DNA extracted from adult tissue of four species of Scylla spp. and the first zoeal stages of S. serrata, S. paramamosain and S. olivacea as template. Using the ITS- 1 region, variation in product fragment length was found to be useful for distinguishing S. serrata and S. olivacea from two other species. The other two species (S. paramamosain and S. tranquebarica) could be identified using the restriction endonuclease Hha I. Using 16S rDNA, all four species were identified using PCR-restriction fragment length polymorphism (RFLP) by double digestion with Dra Ia ndHindIII. These genetic markers can be used for hybridization breeding studies and in field studies of larval and juvenile mud crabs of the genus Scylla.

Estimated Size at Sexual Maturity for Female Mud Crabs (Genus Scylla) from Two Sympatric Species within Ban Don Bay, Thailand

Two species of mud crab, Scylla olivacea and Scylla paramamosain, occur sympatrically in Ban Don Bay, Surat Thani Province, Thailand, with no evidence of interspecific hybridization. These crabs are part of a traditional and largely unregulated fishery within Ban Don Bay. As part of a study of their reproductive biology and the possible mechanisms explaining their lack of hybridization, size at first maturity was compared between females of the two species. Female S. olivacea and S. paramamosain were collected from Ban Don Bay, and their size at first maturity was estimated using three methods relating abdomen width to body size data: the minimum size at maturity, breakpoint analysis, and probit analysis. All three methods employed revealed that female S. paramamosain attain a larger mean size at maturity than female S. olivacea by as much as 18 to 30 mm internal carapace width (ICW). Although the mean size at maturity is different between species, there is an overlap in the size at maturity between the smallest mature S. paramamosain|$({\rm ICW} = 101 \ {\rm mm})$| and the largest immature S. olivacea|$({\rm ICW} = 118 \ {\rm mm})$|⁠. Scylla paramamosain has a generally larger body size than S. olivacea; therefore, it is possible that there is a relationship between body size and the size of functional maturity that prevents hybridization between these two species. However, the overlap in the size at maturity observed between the two species means that there is a margin where size could not be the only isolating mechanism, and therefore, other prezygotic isolating mechanisms must also be responsible for maintaining the sympatric species observed. Based on these findings, it is suggested that the local fishery should operate with a minimum legal size of 100 mm and 130 mm ICW for S. olivacea and S. paramamosain, respectively.

Problems Associated with Tank-held Mud Crab (Scylla spp.) Broodstock

To support studies on the development of broodstock and hatchery technology for mud crabs under the genus Scylla, the SEAFDEC Aquaculture Department maintains captive broodstock in land-based tanks. Disease problems seen in broodstock after being held for three months in these tanks include shell disease due to a combination of fouling organisms and chitinoclastic bacteria, bacterial contamination of the hemolymph, parasitic infestation on the gills and shell, and loss of appendages. Shell disease was manifested as off-white and black patches on the shell, that progressed and became perforations exposing underlying tissues. The hemolymph of a significant number of newly recruited crabs harbored mixed populations of sucrose-fermenting vibrios. Pedunculate cirripedes were found in large numbers both in the gill region and on the shell, boring through and creating perforations in the latter. Nematodes and other saprophytic organisms enter the crab through these perforations. The fouling problems that affect the integrity of the shell are considered to reduce the life span and reproductive potential of captive broodstock under tank conditions; therefore, regular cleaning of the shell is recommended to minimize shell fouling.

Ecology and Management of Mud Crab Scylla spp.

The recent revision of the genus Scylla into four species provides a basis for the develop- ment of a better understanding of their ecology, population biology and the sustainable manage- ment of fisheries, as well as the selection of species for aquaculture. In many cases, previous studies of mud crab fisheries and ecology have reported the occurrence of more than one “type” of mud crab, but data for any one currently known species have rarely been recorded. Consequently, much of the biological and ecological data in the literature must be reviewed. This paper summarizes the current state of knowledge on mud crab ecology in relation to population biology and management, and discusses priorities for future research to support the development of sustainable mud crab aquaculture and fisheries.

Genetic Diversity and Species-Diagnostic Markers of Mud Crabs (Genus Scylla) in Eastern Thailand Determined by RAPD Analysis.

Genetic diversity of three mud crab species, Scylla serrata (Forskål), S. oceanica (Dana), and S. tranquebarica (Fabricius), collected from two locations in eastern Thailand (Chanthaburi and Trat) was examined by randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). Ninety-one reproducible RAPD fragments, generated by UBC456, UBC457, and YNZ22, were polymorphic. The percentage of polymorphic bands within populations ranged from 47.92% to 77.59%. Species-specific RAPD markers were also observed and used to construct a molecular diagnostic key in these taxa. Large genetic differences between species were found (D(ij) = 0.425 to 0.751), whereas those between populations within each species were much lower (D(ij) = 0.171 to 0.199). The neighbor-joining tree based on genetic distances among pairs of individuals indicated three distinct groups, corresponding to S. serrata, S. oceanica, and S. tranquebarica. No genotypes were shared among these three species. This suggests the absence of genetic exchanges between sympatric mud crab species in eastern Thailand. Therefore, mud crabs in this area should be recognized as three different species rather than a single panmictic species exhibiting different morphs.