Plastic ingestion by three species of Scylla (Brachyura) from the coastal areas of Thailand

This study marked the first investigation into the presence of plastic particles in the stomachs of three mud crab species (Scylla olivacea, S. paramamosain and S. tranquebarica) collected across the Andaman Sea and the Gulf of Thailand. The highest number of plastic particles in the stomach of crab samples was polyethylene (PE) that contributed 88.5 %; while green was the predominant colour (60.3 %). Ingested particles recovered from the stomachs of crabs differed significantly between species and sites (p < 0.001). The average number of plastic particles per individual was 2.3 ± 8.6 in Scylla olivacea, 7.2 ± 16.9 in S. paramamosain, and 13.5 ± 48.9 in S. tranquebarica. Satun, revealed the highest number of plastic particles recovered from mud crabs, while the lowest number of plastic particles were from Pattani. To conclude, species of crab and site of collection plays a crucial factor in the propensity of plastic particles ingested by the genus Scylla mud crabs.

Detection of non-ribosomal and polyketide biosynthetic genes in bacteria from green mud crab Scylla serrata gut microbiome and their antagonistic activities

Multi-modular enzyme complexes known as non-ribosomal peptide synthetases (NRPSs) and polyketide synthetases (PKSs) have been widely reported in bacteria that produce secondary bioactive metabolites such as non-ribosomal peptides (NRPs) and polyketides (PKs), respectively. These NRPS/PKS pathways contribute to synthesizing several antibiotics, such as vancomycin, rifamycin, and bleomycin, which are vital in human medicine. The present study aimed to isolate gut-associated bacteria from mud crab Scylla serrata, and detect NRPS and PKS gene clusters associated with it. This study included 36 bacterial isolates from five mud crab gut samples. Biosynthetic gene clusters (NRPS and PKS), were detected by PCR using degenerative primers specific to these genes. Three isolates (FKP2-4, FKP4-1, and FKP2-16) were positive for NRPS and two for PKS (FKP2-4 and FKP4-1) genes. The isolates were subjected to 16S rRNA gene amplification and sequenced. In silico analysis of the sequences using the Basic Local Alignment Search Tool (BLAST) identified the isolates FKP2-4, FKP4-1, and FKP2-16 as Acinetobacter variabilis, Vagococcus fluvialis, and Staphylococcus arlettae, respectively, after comparing with the existing sequences available in the National Center for Biotechnology Information (NCBI) database. Compared to the control, it was observed that these isolates exhibited intriguing antagonistic activities against Escherichia coli and Staphylococcus aureus. However, these isolates failed to show significant activity against Candida albicans. Exopolysaccharide production by the isolated organisms was tested using Zobell marine agar (ZMA) with 5% sucrose, but none of the colonies were mucoid or slimy.

The impact of ocean acidification and cadmium toxicity in the marine crab Scylla serrata: Biological indices and oxidative stress responses

Ocean acidification (OA) and heavy metal pollution in marine environments are potentially threatening marine life. The interactive effect of OA and heavy metals could be more vulnerable to marine organisms than individual exposures. In the current study, the effect of OA on the toxicity of cadmium (Cd) in the crab Scylla serrata was evaluated. Crab instars (0.07 cm length and 0.1 g weight) were subjected to pH 8.2, 7.8, 7.6, 7.4, 7.2, and 7.0 with and without 0.01 mg l-1 of Cd for 60 days. We noticed a significant decrease in growth, molting, protein, carbohydrate, amino acid, lipid, alkaline phosphatase, and haemocytes of crabs under OA + Cd compared to OA treatment. In contrast, the growth, protein, amino acid, and haemocyte levels were significantly affected by OA, Cd, and its interactions (OA + Cd). However, superoxide dismutase, catalase, lipid peroxidation, glutamic oxaloacetate transaminase, glutamic pyruvate transaminase, and accumulation of Cd in crabs were considerably elevated in OA + Cd treatments compared to OA alone treatments. The present investigation showed that the effect of Cd toxicity might be raised under OA on S. serrata. Our study demonstrated that OA significantly affects the biological indices and oxidative stress responses of S. serrata exposed to Cd toxicity.

Pathogenicity of white spot syndrome virus (WSSV) after multiple passages in mud crab, Scylla olivacea

White spot syndrome virus (WSSV) is a highly virulent shrimp pathogen with a broad host range. Among the hosts, though mud crab, Scylla olivacea is reported to be more susceptible to WSSV than S. serrata and S. paramamosain, a detailed study on the pathogenicity and genome stability of the virus after multiple passages has yet to be reported. Firstly, to test the pathogenicity of the virus, WSSV was intramuscularly injected into healthy shrimp, Penaeus vannamei. Experimentally infected P. vannamei showed the first mortality at 36 h post-injection (hpi), followed by 100 % cumulative mortality in 7 days post-injection (dpi). However, S. olivacea injected with the WSSV inoculum derived from infected shrimp showed the first mortality at 48 hpi and a cumulative mortality of 70 % at the end of the ten days experiment. Subsequently, WSSV was sequentially passaged five times in Scylla olivacea to find out any change in the virulence of the virus in each passage. S. olivacea groups injected with 1st, second, third and fourth passages derived from the crab recorded the first mortality between 48 and 56 hpi and the cumulative mortality of 60 to 70 % at the end of the ten days experiment. Injection of WSSV inoculum in P. vannamei derived from multiple passages in S. olivaceae revealed the retention of the pathogenicity of the virus. Shrimp groups injected with WSSV derived from different passages showed first mortality between 24 and 36 hpi and cumulative mortality of 100 % between 6 and 7 dpi. The average viral load in the shrimp groups injected with WSSV inoculum derived from shrimp was 3.6 × 108, whereas in shrimp injected with the inoculum derived from 1st, third and fifth passages from crab showed 4.0 × 108, 4.7 × 108 and 4.3 × 108 copies per 100 ng DNA. Histological examination of the gill and stomach tissue of shrimp injected with inoculum prepared from shrimp as well as the inoculum derived from 1st, third and fifth passages in S. olivacea revealed characteristic pathological manifestations of the WSSV infection in gill and stomach tissues such as hypertrophied nuclei, Cowdry A-type inclusions as well as massive basophilic intranuclear inclusions. Further, to study the genome stability, the primers targeting highly variable regions of the WSSV genome (ORF94, ORF125, ORF75, variable region (VR) 14/15 and VR 23/24) were used to amplify WSSV derived from different passages and the amplified PCR products were sequenced. The sequence analysis revealed the WSSV genome stability after multiple passages in mud crab, S. olivacea.

Integration of microbiome and Koch's postulates to reveal multiple bacterial pathogens of whitish muscle syndrome in mud crab, Scylla paramamosain

BACKGROUND

For more than a century, the Koch's postulates have been the golden rule for determining the causative agents in diseases. However, in cases of multiple pathogens-one disease, in which different pathogens can cause the same disease, the selection of microorganisms that regress infection is hard when Koch's postulates are applied. Microbiome approaches can obtain relatively complete information about disease-related microorganisms and can guide the selection of target microorganisms for regression infection. In the present study, whitish muscle syndrome (WMS) of Scylla paramamosain, which has typical symptoms with whitish muscle and blackened hemolymph was used as an example to establish a new research strategy that integrates microbiome approaches and Koch's postulates to determinate causative agents of multiple pathogens-one disease.

RESULTS

Microbiome results revealed that Aeromonas, Acinetobacter, Shewanella, Chryseomicrobium, Exiguobacterium, Vibrio and Flavobacterium, and Kurtzmaniella in hemolymph were bacterial and fungal indicators for WMS. A total of 23 bacteria and 14 fungi were isolated from hemolymph and muscle tissues, and among the bacteria, Shewanella chilikensis, S. xiamenensis, Vibrio alginolyticus, S. putrefaciens, V. fluvialis, and V. parahaemolyticus were present in hemolymph and/or muscle tissues in each WMS crab, and the last three species were also present in three Healthy crabs. The target bacteria and fungi were further screened to regression infections based on two criteria: whether they belonged to the indicator genera for WMS, whether they were isolated from both hemolymph and muscle tissues in most WMS crabs. Only S. chilikensis, S. putrefaciens, S. xiamenensis, V. alginolyticus, V. fluvialis, and V. parahaemolyticus met both two criteria. The six bacteria that met both two criteria and six fungi and another bacterium that unmatched any of two criteria were used to perform regression infection experiments based on Koch's postulates. S. chilikensis, S. putrefaciens, S. xiamenensis, V. alginolyticus, V. fluvialis, and V. parahaemolyticus met both two criteria, and the results indicate that they cause WMS in crabs independently.

CONCLUSIONS

This study fully demonstrated that our research strategy that integrates the microbiome and Koch's postulates can maximize the ability to catch pathogens in one net for the situation of multiple pathogens-one disease. Video Abstract.

The role of Nrf2 signaling pathway in the mud crab (Scylla paramamosain) in response to Vibrio parahaemolyticus infection

The transcription factor Nrf2 plays vital roles in detoxification and antioxidant enzymes against oxidative stress. However, the function of Nrf2 in crustaceans is not well studied. In this study, a novel Nrf2 gene from the mud crab (Sp-Nrf2) was identified. It was encoded 245 amino acids. Sp-Nrf2 expression was ubiquitously expressed in all tested tissues, with the highest expression level in the gill. Sp-Nrf2 protein was mainly located in the nucleus. The expression levels of Sp-Nrf2, and antioxidant-related genes (HO-1 and NQO-1) were induced after Vibrio parahaemolyticus infection, indicating that Nrf2 signaling pathway was involved in the responses to bacterial infection. Over-expression of Sp-Nrf2 could improve cell viability after H₂O₂ exposure, indicating that Sp-Nrf2 might relieve oxidative stress. Silencing of Sp-Nrf2 in vivo decreased HO-1 and NQO-1 expression. Moreover, knocking down Sp-Nrf2 in vivo can increase malondialdehyde content and the mortality of mud crabs after V. parahaemolyticus infection. Our results indicated that Nrf2 signaling pathway played a significant role in immune response against bacterial infection.

Comparative Analyses of Scylla olivacea Gut Microbiota Composition and Function Suggest the Capacity for Polyunsaturated Fatty Acid Biosynthesis

Although numerous studies in aquatic organisms have linked lipid metabolism with intestinal bacterial structure, the possibility of the gut microbiota participating in the biosynthesis of beneficial long-chain polyunsaturated fatty acid (LC-PUFA) remains vague. We profiled the gut microbiota of the mud crab Scylla olivacea fed with either a LC-PUFA rich (FO) or a LC-PUFA-poor but C18-PUFA substrate-rich (LOCO) diet. Additionally, a diet with a similar profile as LOCO but with the inclusion of an antibiotic, oxolinic acid (LOCOAB), was also used to further demarcate the possibility of LC-PUFA biosynthesis in gut microbiota. Compared to diet FO treatment, crabs fed diet LOCO contained a higher proportion of Proteobacteria, notably two known taxonomy groups with PUFA biosynthesis capacity, Vibrio and Shewanella. Annotation of metagenomic datasets also revealed enrichment in the KEGG pathway of unsaturated fatty acid biosynthesis and polyketide synthase-like system sequences with this diet. Intriguingly, diet LOCOAB impeded the presence of Vibrio and Shewanella and with it, the function of unsaturated fatty acid biosynthesis. However, there was an increase in the function of short-chain fatty acid production, accompanied by a shift towards the abundance of phyla Bacteroidota and Spirochaetota. Collectively, these results exemplified bacterial communities and their corresponding PUFA biosynthesis pathways in the microbiota of an aquatic crustacean species.

Health risk assessment of metals in mud crab (Scylla serrata) from the East Java Estuaries of Indonesia

Metals accumulating in mud crab from Indonesia's East Java estuaries have been assessed for potential health effects. Mud crabs from the Solo River estuary (JS) had the highest levels of all metals tested when compared to mud crabs from the Brantas River estuary (MS) and the Banyuwangi coastal area (BS). Metal accumulation in mud crabs occurred in the following order: Zn > Cu > Cr > Pb > Cd > Hg. The estimated weekly intake values for all metals from all stations were less than the provisional tolerable weekly intake requirement. Similarly, all metal target hazard quotient values from all stations were less than one, suggesting that all metals were within the allowable intake limit. The target cancer risk values for Cd and Cr, on the other hand, were somewhat higher than 10^-4, indicating that they were dangerous for human ingestion and possibly linked to a risk associated with carcinogenic agent exposure over a lifetime.

Monodon baculovirus (MBV) infects wild mud crab, Scylla serrata

During a survey of farmed and wild crustaceans from India for viruses, spherical baculovirosis otherwise known as Penaeus monodon-type baculovirus (MBV) was detected in field-collected juvenile/sub-adult mud crab, Scylla serrata using a nested polymerase chain reaction (PCR)-based amplification of the hepatopancreatic DNA. Eight out of 115 mud crab (7.0%) examined during the study were found to be positive in the nested PCR resulting in a 361 nt amplicon. Mud crab, S. olivacea and other crustaceans such as marine crab, Portunus sanguinolentus and farmed penaeid shrimp, Penaeus vannamei and P. monodon were tested negative for the virus. Further, degenerate primers reported to amplify polyhedrin protein gene of MBV also showed PCR amplification in one of the MBV-positive crab samples resulting in a 250 nt amplicon. Sequencing of the two target amplicons (MBV- 361 nt and MBV polyhedrin - 216 nt) revealed more than 97.5 % and 92.8% sequence identity, respectively with the Penaeus monodon nudivirus and Penaeus monodon nucleopolyhedrovirus (MBV) reported from shrimp. Further, histological analysis of mud crab revealed nuclear hypertrophy, chromatin margination and intranuclear eosinophilic/basophilic inclusions in tubule epithelium of hepatopancreas. The hepatopancreatic tissue also showed unusually large, eosinophilic/basophilic inclusion-like structures. These inclusions resembled the viral inclusions reported from S. serrata from Australia. This is the first record of monodon-type baculovirus from a crab host and the second from a non-penaeid crustacean. Interestingly, some of the crab samples also showed deeply basophilic intranuclear inclusion-like bodies resembling hepatopancreatic parvovirus group of viruses (HPV). However, none of the crab samples subjected to PCR amplification using HPV-specific primers showed any amplification. The histological observations made in the present study indicate the possibility of the presence of two hepatopancreas-infecting viruses in S. serrata from India.

Comparative transcriptome profiling of heat stress response of the mangrove crab Scylla serrata across sites of varying climate profiles

Background

The fishery and aquaculture of the widely distributed mangrove crab Scylla serrata is a steadily growing, high-value, global industry. Climate change poses a risk to this industry as temperature elevations are expected to threaten the mangrove crab habitat and the supply of mangrove crab juveniles from the wild. It is therefore important to understand the genomic and molecular basis of how mangrove crab populations from sites with different climate profiles respond to heat stress. Towards this, we performed RNA-seq on the gill tissue of S. serrata individuals sampled from 3 sites (Cagayan, Bicol, and Bataan) in the Philippines, under normal and heat-stressed conditions. To compare the transcriptome expression profiles, we designed a 2-factor generalized linear model containing interaction terms, which allowed us to simultaneously analyze within-site response to heat-stress and across-site differences in the response.

Results

We present the first ever transcriptome assembly of S. serrata obtained from a data set containing 66 Gbases of cleaned RNA-seq reads. With lowly-expressed and short contigs excluded, the assembly contains roughly 17,000 genes with an N50 length of 2,366 bp. Our assembly contains many almost full-length transcripts – 5229 shrimp and 3049 fruit fly proteins have alignments that cover >80% of their sequence lengths to a contig. Differential expression analysis found population-specific differences in heat-stress response. Within-site analysis of heat-stress response showed 177, 755, and 221 differentially expressed (DE) genes in the Cagayan, Bataan, and Bicol group, respectively. Across-site analysis showed that between Cagayan and Bataan, there were 389 genes associated with 48 signaling and stress-response pathways, for which there was an effect of site in the response to heat; and between Cagayan and Bicol, there were 101 such genes affecting 8 pathways.

Conclusion

In light of previous work on climate profiling and on population genetics of marine species in the Philippines, our findings suggest that the variation in thermal response among populations might be derived from acclimatory plasticity due to pre-exposure to extreme temperature variations or from population structure shaped by connectivity which leads to adaptive genetic differences among populations.

Supplementary Information

The online version contains supplementary material available at (10.1186/s12864-021-07891-w).

Environmental salinity and dietary lipid nutrition strategy: Effects on flesh quality of the marine euryhaline crab Scylla paramamosain

The quality of crustaceans' flesh has direct impact on consumers' purchase choices, with water environment and dietary nutrition being effective ways to regulate flesh quality. The aim of present study was to investigate the impacts of water salinity (low, 4 and medium, 23) and dietary lipid source (fish oil and soybean oil) on nutritional values, texture, taste and odor of flesh of mud crab. While water salinity had no significant influence on nutritional values of crab flesh, crabs fed soybean oil displayed significantly lower contents of amino acids and n-3 PUFAs in muscle. However, crabs reared at low salinity showed reduced flesh hardness, chewiness and gumminess likely related to altered myofiber structure, that impacted muscle texture. Furthermore, low salinity and dietary soybean oil weakened umami taste and aroma characteristics of crab flesh associated with decreased contents of free amino acids, flavor nucleotides, inorganic ions and odor active compounds in flesh.

Chemosensitivity and role of swimming legs of mud crab, Scylla paramamosain, in feeding activity as determined by electrocardiographic and behavioural observations

Swimming crabs have a characteristic fifth pair of legs that are flattened into paddles for swimming purposes. The dactyl of these legs bears a thick seta along its edge. The chemoreceptive and feeding properties of the seta are supported with scientific evidence; however, there is no available data on the sensitivity of the setae in portunid crabs. The underlying mechanisms of the chemo- and mechano-sensitivity of appendages and their involvement in feeding activities of the mud crab (Scylla paramamosain) were investigated using electrocardiography and behavioural assay, which focused on the responses of the mud crab to chemical and touch stimulus. Electrocardiography revealed the sensory properties of the appendages. The dactyls of swimming legs and the antennules were chemosensitive, but not mechanosensitive and vice versa for the antennae. However, the mouthparts, claws, and walking legs were chemo- and mechanosensitive. Only the chemosensitive appendages, including the swimming legs, were directly involved in feeding. The flattened dactyls of the swimming legs were more efficient than the pointed dactyls of the walking legs in detecting the food organism crawling on the substrate. The structural features enhanced the capacity of the crab in coming into contact with scattered food items. This study revealed that the swimming legs are important appendages for feeding in the mud crab.

Large lipid transfer proteins in hepatopancreas of the mud crab Scylla paramamosain

Large lipid transfer proteins (LLTPs) are extensively involved in various physiological processes. In the present study, five LLTP sequences encoding apolipocrustacein 1 (apoCr 1), apoCr 2, precursor of the large discoidal lipoprotein (dLp) and high density lipoprotein/β-glucan binding protein (HDL-BGBP) (dLp-BGBP), microsomal triglyceride transfer protein (MTP) and clotting protein (CP) were identified in the hepatopancreas of Scylla paramamosain. Of these, apoCr 2, dLp-BGBP, and MTP were newly identified in this species, and the former two proteins were classified into the APO family while the later into the MTP family in phylogenetic trees. The apoCr 1 expression level was dramatically increased in the hepatopancreas towards ovarian maturation, which was extremely greater than that in the ovaries concurrently, likely to meet the considerable requirements of yolk protein and lipids for embryo development. The dLp-BGBP expression level in male crabs was comparable to that in female crabs, supporting HDL-BGBP acts as a major circulatory lipid carrier. The close phylogenetic relationship between dLp-BGBP and the scaffolding protein of lipid transfer particle implied dLp might facilitate lipid transfer between the hepatopancreas and HDL-BGBP-containing lipoproteins. The MTP expression level was positively related to ovarian development in both the hepatopancreas and ovaries, indicating MTP may be involved in lipoprotein assembly in the hepatopancreas and lipid droplet maturation in the ovaries. CP may play a crucial role in embryo development based on high expression level observed in the testes of mature crabs. Our findings provide novel insights into LLTP superfamily members and their functions in decapods.

Reference gene and tropomyosin expression in mud crab Scylla olivacea, Scylla paramamosain and Scylla tranquebarica

Tropomyosin, a muscle tissue protein is a major allergen in most of shellfish including mud crab. Quantitative real time-PCR (qRT-PCR) using a stable reference gene is the most sensitive approach to produce accurate relative gene expression that has yet to be demonstrated for allergenic tropomyosin in mud crab species. This study was conducted to identify the suitable reference gene and tropomyosin expression in different body parts of local mud crabs, Scylla olivacea, Scylla paramamosain and Scylla tranquebarica. Myosin, 18S rRNA, GADPH and EF1α were selected as candidate reference genes and their expression was measured in the abdomen, walking leg and cheliped tissues of local Scylla spp. The expression stability was analyzed using the comparative delta-Ct method, BestKeeper, NormFinder and geNorm then comprehensively ranked by RefFinder algorithm. Findings showed that EF1α was the most suitable reference gene across three mud crab species. Meanwhile, the abdomen, walking leg and cheliped selected their own suitable reference gene either Myosin, 18S rRNA, EF1α or GADPH. Overall, tropomyosin was the highest in S. tranquebarica, whereas the least was in S. paramamosain. Interestingly, tropomyosin was the highest in the abdomen of all mud crab species. This is the first analysis on reference genes selection for qRT-PCR data normalization of tropomyosin expression in mud crab. These results will provide more accurate findings for further gene expression and allergen analysis in Scylla spp.

Diverse land uses and high coastal urbanisation do not always result in harmful environmental pollutants in fisheries species

Human activities in coastal catchments can cause the accumulation of pollutants in seafood. We quantified the concentration of heavy metals, pesticides and PFASs in the flesh of the fisheries species yellowfin bream Acanthopagrus australis (n = 57) and mud crab Scylla serrata (n = 65) from 13 estuaries in southeast Queensland, Australia; a region with a variety of human land uses. Pollutants in yellowfin bream were best explained by the extent of intensive uses in the catchment. Pollutants in mud crabs were best explained by the extent of irrigated agriculture and water bodies. No samples contained detectable levels of pesticides, and only six samples contained low levels of PFASs. Metals were common in fish and crab flesh, but only mercury in yellowfin bream from the Mooloolah River breached Australian food safety standards. High pollutant presence and concentration is not the norm in seafood collected during routine surveys, even in estuaries with highly modified catchments.

Immune and physiological responses of mud crab (Scylla paramamosain) under air exposure

The immune and physiological responses of mud crab (Scylla paramamosain) under air exposure were studied. The results showed that air exposure increased plasma activities of AST, ALT, ALP. There was a significant increase in glucose (GLU) and malondialdehyde (MDA) levels after air exposure. The transcript levels of SOD, CAT, HSP90, HSP70, p53, and hypoxia-inducible factor-1 (HIF-1) were induced by air exposure. Furthermore, caspase-3 transcript significantly increased at 48 and 72 h, while it significantly decreased at 96 h and 120 h under air exposure. These results suggested that oxidative stress occurred in the prolonged period of air exposure. HIF-1 and p53 signaling pathways played an important role under air exposure.

Role of crustacean female sex hormone (CFSH) in sex differentiation in early juvenile mud crabs, Scylla paramamosain

Recent studies have shown that crustacean female sex hormone (CFSH) is involved in the development of reproductive phenotype. In the present study, observation of sexually dimorphic traits revealed that gender could be distinguished from the third stage juveniles onwards in the mud crab, Scylla paramamosain. Sp-cfsh expression levels were analyzed in early juveniles. The results showed that, Sp-cfsh expression levels differed among individuals at post-molt of the first stage and second stage, and significantly different between the two sexes at post-molt of the third stage, which suggested that Sp-cfsh might participate in the sex differentiation in early juveniles. The expression of Sp-cfsh was examined during the molting cycle at the third stage juveniles, and the results showed that it was highest at the pre-molt stage. Based on the results, the expression of Sp-cfsh at pre-molt stage was further analyzed between the sexes from the third stage to the fifth stage, and it was found that the expression of Sp-cfsh was similar between two sexes at the third stage and the fourth stage; whereas at the fifth stage, when the gonopores occurred, the expression of Sp-cfsh significantly increased in females but decreased in males; suggesting that the expression of Sp-cfsh could influence the formation of gonopores. Finally, the role of Sp-cfsh in the reproductive phenotypes was confirmed through RNA interference knockdown. The combined results suggest that CFSH is involved in the regulation of sex differentiation of early juvenile in S. paramamosain.

Reassessment of species distribution and occurrence of mud crab (Scylla spp., Portunidae) in Malaysia through morphological and molecular identification

This study utilized genetic and morphometric approaches to assess the molecular and morphometric differentiation among commercially important species of mud crab. Molecular investigations were derived from 542 bp mitochondrial DNA COI on 249 individuals within genus Scylla from nine states in Malaysia represents four marine regions; South China Sea, Sulu Sea, Straits of Singapore and Straits of Malacca. Four specimens were obtained from Indonesia to give a robust analysis in this study. For species delimitation, Automatic Barcode Gap Discovery (ABGD) method on a web interface was employed. Analysis on phylogenetics was implemented utilizing Neighbour joining (NJ) and Maximum Parsimony (MP) methods. The inter- and intraspecies genetic distances (D_s) was computed using Kimura 2-parameter distance and executed in MEGA version 5.05. All samples were genetically and morphologically identified and clustered into four distinct species. Among the species, S. olivacea was the most abundant (n = 111), on the other hand the occurrence of S. paramamosain in Malaysia was very low (n = 29). No single individual of S. serrata from Malaysia was recorded in this study. Both genetic distance and phylogenetic approaches exhibited a correlative monophyletic association among all specimens analysed. This present study is crucial as it reports the reassessment of all species within genus Scylla in Malaysia, eventually could be employed as a reference source for subsequent research mainly on mariculture and other conservation efforts for the species.

Bioaccumulation of heavy metals (Hg, Cd and Ni) by sentinel crab (Macrophthalmus depressus) from sediments of Mousa Bay, Persian Gulf

The presence of heavy metals (HMs) in the environment can increase their risk of transfer to the food chain. The present study was conducted to investigate the bioaccumulation of HMs including Hg, Cd and Ni in soft and hard tissues of sentinel crab (Macrophthalmus depressus Rüppell, 1830) in sediments of Mousa Bay in northwest of the Persian Gulf. The average (mean ± SD) amounts of Hg, Cd and Ni in the sediments were 6.27 ± 3.66, 3.8 ± 1.48 and 71.6 ± 5.09 μg/g, whereas the relevant amounts for soft tissues were 6.16 ± 4.64, 3.3 ± 1.7 and 19.7 ± 3.96 μg/g, and for hard tissues were, 2.9 ± 1.67, 3.5 ± 1.35 and 10.44 ± 3.1 μg/g, respectively. Accordingly, soft tissues of the crab could be suitable bioindicators of Hg and Cd, whereas the hard tissues could be used as Cd bioindicator. Since the bioaccumulation of Ni was the most, it might have a higher risk among the metals to enter the food chain in the region.

Pattern recognition receptors and their roles on the innate immune system of mud crab (Scylla paramamosain)

The innate immune system is the first line of defense protecting the hosts against invading pathogens. Mud crab (Scylla paramamosain) is widely distributed in China and Indo-west Pacific countries, which develops a very complicated innate immune system against pathogen invasions. Innate immunity involves the humoral and cellular responses that are linked to the pattern recognition receptors (PRRs). PRRs initially recognize the infection and trigger the activation of signaling cascades, leading to transcriptional regulation of inflammatory mediators that function in pathogenic control and clearance. In mud crab S. paramamosain, the Toll/Toll-like receptors, lipopolysaccharide and β-1,3-glucan binding proteins, C-type lectins, scavenger receptors, and down syndrome cell adhesion molecules have been identified as receptor families responsible for the recognition of bacteria, fungi, and viruses, and are important components in the innate immune system. In this review, we summarize the literature on the current knowledge and the roles of PRRs in the immune defenses of mud crab, which in an effort to provide much information for further researches.

Source of hemolymph microbiota and their roles in the immune system of mud crab

Special innate immune mechanisms against pathogens are developed in marine invertebrates such as mud crab, which is also an economically important aquaculture species in many coastal countries. Hemolymph is a critical site in host immune response, but its source of microorganisms is less known. In this study, we provided a detailed investigation of the microorganisms inhabiting various body sites of healthy mud crabs, including hemolymph, midgut, gill, subcuticular epidermis and hepatopancreas. By using fluorescence microscopy and high-throughput sequencing of the bacterial 16S rRNA genes, various abundances and kinds of microorganisms were observed in the healthy mud crabs, of which some are potential pathogens to mud crab and human. The SourceTracker analysis and oral injection experiment confirm the hypothesis that hemolymph microorganisms are derived from the digestive systems of invertebrates with open circulatory systems, indicating that these microorganisms play vital roles in crab immune response. Moreover, physiological differences (gut length), behavioral characteristics (foraging behavior), diet preferences (herbivory), and/or sex hormones (testosterone) possibly determine the unique features of the crab-associated microbiota for both sexes. These findings also contribute to the development of appropriate microbial immunoenhancers, which has potential applications for improving quality and yield during crab aquaculture.

SpBAG1 promotes the WSSV infection by inhibiting apoptosis in mud crab (Scylla paramamosain)

Bcl-2 associated athanogene-1 (BAG1) is involved in various signalling pathways including apoptosis, cell proliferation, gene transcriptional regulation and signal transduction in animals. However the functions of BAG1 during the antiviral response of mud crab Scylla paramamosain is still unclear. In this study, the mud crab BAG1 (SpBAG1) was characterized to consist of 1761 nucleotides, containing an opening frame of 630bp encoding 209 amino acids with an ubiquitin domain and a BAG1 domain. SpBAG1 was found to be significantly up-regulated at 6 h-24 h, but down-regulated from 48 h-72 h in the hemocytes of mud crab after challenge with white spot syndrome virus (WSSV). RNAi knock-down of SpBAG1 significantly reduced the copies of WSSV and increased the apoptotic rate in mud crabs. The finding from this study suggested that SpBAG1 could promote the WSSV infection by inhibiting apoptosis in mud crab. Therefore, to the best of our knowledge, this is the first study demonstrating the role of SpBAG1 as a novel apoptosis inhibitor to promote virus infection in mud crab.

Lactic acid bacteria, Enterococcus faecalis Y17 and Pediococcus pentosaceus G11, improved growth performance, and immunity of mud crab (Scylla paramamosain)

Mud crabs (Scylla paramamosain), a commercially important cultured species in the southeastern region of China, is usually infected by Vibriosis or parasites, causing great economic losses in cultured farms. Previous studies have demonstrated that probiotics benefited in enhancing the immune response against invading pathogens in aquatic animals. In this study, the effects of dietary administration of lactic acid bacteria (LAB) (Enterococcus faecalis Y17 and Pediococcus pentosaceus G11) on growth performance and immune responses of mud crab were assessed. Both strains (Y17 and G11) showed an inhibitory activity against bacterial pathogens (Aeromonas hydrophila, Vibrio parahaemolyticus, Vibrio alginolyticus, Staphylococcus aureus, and β Streptococcus), and a wide pH tolerance range of 2-10. In vivo, mud crabs were fed a control diet and experimental diets supplemented with 10⁹ cfu g^-1 diet either Y17 or G11 for 6 weeks before subjecting to a challenge test with V. parahaemolyticus for 12 h. The probiotic-supplemented diets had significant effects on weight gain and specific growth rate during the feeding trial. Increased serum enzyme activities of phenoloxidase, lysozyme, and SOD were observed in the hemolymph of mud crab in Y17 and G11-supplemented groups compared to that in the controls (P < 0.01). The significantly up-regulated expression of gene CAT, LYS, proPO, and SOD could be seen in hepatopancreas in G11-supplemented groups. After the pathogenicity test, the survival rate of Y17 + and G11 + V. parahaemolyticus groups was 66.67% and 80.00%, respectively, compared with 53.33% for the control groups. Taken together, dietary supplementation of Y17 and G11 strains were beneficial in mud crab, which could increase growth performance, modulate immune system and protect the host against V. parahaemolyticus infection.

Molecular characterization of a vitellogenesis-inhibiting hormone (VIH) in the mud crab (Scylla olivacea) and temporal changes in abundances of VIH mRNA transcripts during ovarian maturation and following neurotransmitter administration

The vitellogenesis-inhibiting hormone (VIH), also known as gonad-inhibiting hormone, is a neuropeptide hormone in crustaceans that belongs to the crustacean hyperglycemic hormone (CHH)-family peptide. There is regulation vitellogenesis by VIH during gonad maturation in crustaceans. A full-length Scylla olivacea VIH (Scyol-VIH) was identified through reverse transcription polymerase chain reaction and rapid amplification of cDNA ends. The open reading frame consists of 378 nucleotides, which encodes a 126-amino acid precursor protein, including a 22-residue signal peptide and a 103-amino acid mature peptide in which 6 highly conserved cysteine residues are present. There was expression of the Scyol-VIH gene in immature female Scylla olivacea in the eyestalk, brain and ventral nerve cord. The Scyol-VIH gene expression was localized to the eyestalk X-organ, brain neuronal clusters 6 and 11, and in multiple neuronal clusters of the ventral nerve cord. The relative abundance of Scyol-VIH mRNA transcript in the eyestalk was relatively greater in immature stage females, then decreased as ovarian maturation progressed. Furthermore, eyestalk Scyol-VIH increased after dopamine (5 μg/g BW) injection. The present research provides fundamental information about Scyol-VIH and its potential effect in controlling reproduction.

Proteomic analysis and white spot syndrome virus interaction of mud crab (Scylla olivacea) revealed responsive roles of the hemocytes

White spot disease (WSD) is a highly virulent viral disease in shrimps. Clinical signs and high mortality of WSD is generally observed after a few days of infection by White Spot Syndrome virus (WSSV). Mud crabs are the major carrier and persistent host for the WSSV. However, an elucidation of viral interaction and persistent mode of WSSV infection in mud crab is still limited. We investigated the defensive role of mud crab (Scylla olivacea) hemocytes against WSSV infection by using comparative proteomic analysis coupled with electrospray ionization liquid chromatography tandem mass spectrometry (ESI-LC/MS/MS). The proteomic maps of expressed proteins obtained from WSSV infected hemocytes revealed differential proteins related to various biological functions, including immune response, anti-apoptosis, endocytosis, phosphorylation signaling, stress response, oxygen transport, molting, metabolism, and biosynthesis. Four distinctive cell types of crab hemocytes: hyaline cells (HC), small granular cells (SGC), large granular cells (LGC) and mixed granular cells (MGC) were found susceptible to WSSV. However, immunohistochemistry analysis demonstrated a complete replication of WSSV only in SGC and LGC. WSSV induced apoptosis was also observed in HC, SGC and MGC except for LGC. These results suggested that HC and MGC may undergo apoptosis prior to a complete assembly of virion, while SGC is more susceptible showing higher amplification and releasing of virion. In contrast, WSSV may inhibit apoptosis in infected LGC to stay in latency. This present finding provides an insight for the responsive roles of crustacean hemocyte cells involved in molecular interaction and defense mechanism against WSSV.

Gonadal microRNA Expression Profiles and Their Potential Role in Sex Differentiation and Gonadal Maturation of Mud Crab Scylla paramamosain

Although the sexual dimorphism in terms of gonadal development and gametogenesis of mud crab has been described, the internal regulating mechanism and sex differentiation process remain unclear. A comparative gonadal miRNA transcriptomic study was conducted to identify miRNAs that are differentially expressed between testes and ovaries, and potentially uncover miRNAs that might be involved in sex differentiation and gonadal maturation mechanisms of mud crabs (Scylla paramamosain). A total of 10 known miRNAs and 130 novel miRNAs were identified, among which 54 were differentially expressed. Target gene prediction revealed a significant enrichment in 30 KEGG pathways, including some reproduction-related pathways, e.g. phosphatidylinositol signalling system and inositol phosphate metabolism pathways. Further analysis on six differentially expressed known miRNAs, six differentially expressed novel miRNAs and their reproduction-related putative target genes shows that both miRNAs and putative target genes showed stage-specific expression during gonadal maturation, suggesting their potential regulatory roles in sex differentiation and reproductive development. This study reveals the sex-biased miRNA profile and establishes a solid foundation for understanding the sex differentiation and gonadal maturation mechanisms of S. paramamosain.

A novel crustacean hyperglycemic hormone (CHH) from the mud crab Scylla paramamosain regulating carbohydrate metabolism

Crustacean hyperglycemic hormone (CHH) plays a crucial role in regulating carbohydrate metabolism in crustaceans. In this study, a new cDNA encoding type I CHH peptide, termed Sp-CHH3, was isolated from the mud crab Scylla paramamosain and its potential functions were investigated. The full length cDNA of Sp-CHH3 was identified as encoding a 127-aa precursor composed of a 27-aa signal peptide, a 23-aa CHH precursor-related peptide and a 75-aa mature peptide with a typical motif of CHH. Phylogenic analysis suggested that, Sp-CHH3 is a previously unreported CHH from S. paramamosain. Tissue distribution analysis showed that Sp-CHH3 was mainly expressed in the eyestalk ganglia, thoracic ganglia, stomach and the ovary. A RNA interference experiments showed that after injection of Sp-CHH3-targeted dsRNA, both the level of Sp-CHH3 expression in the eyestalk ganglia and hemolymph glucose level decreased significantly. A further short-term starvation experiments demonstrated that, the level of Sp-CHH3 detected in the eyestalk ganglia was significantly up-regulated at the 12th h of starvation, it then fell back at the 24th h of starvation and subsequently remained relative stability between the 24th to 96th h of starvation. The hemolymph glucose level decreased significantly (P < .05) at each sampling time during the 96 h starvation duration when compared to that of 0 h (prior to starvation) and the overall trend was largely correlated with the level of Sp-CHH3 expression in the eyestalk ganglia. In summary, the results suggest that Sp-CHH3 plays a functional role in regulating carbohydrate metabolism in S. paramamosain.

Identifying neuropeptide GPCRs in the mud crab, Scylla paramamosain, by combinatorial bioinformatics analysis

Neuropeptides, ubiquitous signaling molecules, commonly achieve their signaling function via interaction with cell membrane-spanning G-protein coupled receptors (GPCRs). In recent years, in the midst of the rapid development of next-generation sequencing technology, the amount of available information on encoded neuropeptides and their GPCRs sequences have increased dramatically. The repertoire of neuropeptides has been determined in many crustaceans, including the commercially important mud crab, Scylla paramamosain; however, determination of GPCRs is known to be more difficult and usually requires in vitro binding tests. In this study, we adopted a combinatorial bioinformatics analysis to identify S. paramamosain neuropeptide GPCRs. A total of 65 assembled GPCR sequences were collected from the transcriptome database. Subsequently these GPCRs were identified by comparison to known neuropeptide GPCRs based on the sequence-similarity-based clustering and phylogenetic analysis, which showed that many of them are closely related to insect GPCR families. Of these GPCRs, most of them were detected in various tissues of the mud crab and some of them showed differential expression by gender, suggesting they are involved in different physiological processes, such as sex differentiation. By employing ligand-receptor binding tests, we demonstrated that the predicted crustacean cardioactive peptide (CCAP) receptor was activated by CCAP peptide in a dose-dependent manner. This is the first CCAP receptor that has been functionally defined in crustaceans. In summary, the present study shortlists candidate neuropeptide GPCRs for ligand-receptor binding tests, and provides information for subsequent future research on the neuropeptide/GPCR signaling pathway in S. paramamosain.

Protein Profile and Ammonia Excretion of Mud Crab <I>Scylla serrata</I> with Recirculation System

BACKGROUND AND OBJECTIVE

Mud crabs have a high level of cannibalism so as to increase the growth of maximum mud crab and reduce the level of stress it is necessary environmental manipulation that supports it as a container maintenance with dark and bright conditions. This study aimed to determine the optimum container condition for survival and growth of mud crab by protein profile and ammonia excretion.

MATERIALS AND METHODS

Mud crab derived from the fisherman Pasuruan East Java with initial weight 45-65 g kept in containers (60×40×30 cm3) in recirculation systems for 42 days with feeding trash fish restricted by 5% twice daily. The study was conducted with two treatments and three replications of bright containers and dark containers. Several stress indicators including protein retention, total serum protein, ammonia secretion were determined and growth performance of the mud crab was also evaluated.

RESULTS

The dark container resulted in optimum condition for mud crab indicated by the highest survival 30±6%, specific growth rate 0.44±0.02%/day, absolute longevity 1.29±0.03 cm, absolute weight growth 10.5±0.31 g, protein retention 15.59±0.46% and feed conversion ratio 6.38±0.27.

CONCLUSION

This study concluded that better growth performance was observed in dark container for nursery of mud crabs.

Study on Carapace Width Growth Band Counts Relationship of Orange Mud Crab, Scylla olivacea (Herbst, 1796) from Terengganu Coastal Waters, Malaysia

BACKGROUND

Orange mud crab Scylla olivacea is one of the most important fisheries resources. A new development in ageing technique of crustaceans has been introduced. The detection of growth band deposited in hard structure of gastric mill in the cardiac stomach are found retained after moulting process can be used as age indicator and growth estimation.

OBJECTIVE

This study was carried out to determine the comparison between carapace width and growth band count of S. olivacea in Malaysia.

MATERIALS AND METHODS

Samples were collected from Setiu Wetlands, Terengganu, Malaysia from February until August, 2016. Samples were categorized based on their morphological measurements. The mesocardiac and zygocardiac ossicles in the gastric mill of S. olivacea was dissected out and preserved in solutions and underwent a cross sectioning process. A total of 76 of wild S. olivacea ranging from 6.56 to 12.84 cm in carapace width were analysed. The growth band counts were examined for each individual and ranging from 1 to 3 band counts.

RESULTS

A positive linear relation was observed between CW and GBC with r2 = 0.5178, p<0.01. Overall, there was a strong, positive correlation between CW and GBC. Increase in CW were correlated with increases in GBC respectively for this species.

CONCLUSION

Therefore, the carapace width, growth band counts and body weight can be used to improve data on growth, recruitment, maturation and mortality. Thus, this study would able to improve new ageing technique and contribute greatly to improve the conservation and management of S. olivacea in Setiu Wetlands, Terengganu, Malaysia.

Infestation of parasitic rhizocephalan barnacles Sacculina beauforti (Cirripedia, Rhizocephala) in edible mud crab, Scylla olivacea

Screening of mud crab genus Scylla was conducted in four locations (Marudu Bay, Lundu, Taiping, Setiu) representing Malaysia. Scylla olivacea with abnormal primary and secondary sexual characters were prevalent (approximately 42.27% of the local screened S. olivacea population) in Marudu Bay, Sabah. A total of six different types of abnormalities were described. Crabs with type 1 and type 3 were immature males, type 2 and type 4 were mature males, type 5 were immature females and type 6 were mature females. The abdomen of all crabs with abnormalities were dented on both sides along the abdomen’s middle line. Abnormal crabs showed significant variation in their size, weight, abdomen width and/or gonopod or pleopod length compared to normal individuals. The mean body weight of abnormal crabs (type 1–5) were higher than normal crabs with smaller body size, while females with type 6 abnormality were always heavier than the normal counterparts at any given size. Sacculinid’s externa were observed in the abdomen of crabs with type 4 and type 6 abnormalities. The presence of embryos within the externa and subsequent molecular analysis of partial mitochondrial COI region confirmed the rhizocephalan parasite as Sacculina beauforti. Future in-depth descriptions of the life cycle and characteristics of S. beauforti are recommended as it involves a commercially important edible crab species and the effect on human health from the consumption of crabs is of crucial concern.

Molecular cloning, mRNA expression and nutritional regulation of a Δ6 fatty acyl desaturase-like gene of mud crab, Scylla paramamosain

Fatty acyl desaturases (Fads) are critical enzymes in the pathways for the biosynthesis of the highly unsaturated fatty acids (HUFA). Here we report on the molecular cloning, tissue expression and nutritional regulation of a Δ6 fatty acyl desaturase-like (Δ6 Fad-like) gene from mud crab, Scylla paramamosain. The full-length cDNA was 1973bp, with a 201bp of 5'-UTR, a 443bp of 3'-UTR, and an ORF of 1329bp that encoded a protein of 442 amino acids. Bioinformatics analysis showed that the deduced peptide sequence possessed the typical features of the microsomal Fads, including N-terminal cytochrome b₅ domain containing the heme-binding motif (H-P-G-G), three histidine-rich boxes and three membrane-spanning regions. Sequence comparison revealed that the predicted protein had a high percentage identity (>53%) with Δ6 Fads from other crustacean species. The tissue distribution of mud crab Δ6 Fad-like mRNA was found predominantly in hepatopancreas, with lower expression levels in all other tissues. Quantitative real-time PCR showed that the Δ6 Fad-like transcriptional levels in hepatopancreas gradually increased with the increased replacement of dietary fish oil (FO) by soybean oil (SO). The replacement ratio of FO by SO up to 60%, 80%, and 100% were significantly up-regulated by about 2.40-fold, 2.99-fold and 3.02-fold compared with that in the control group (100% FO) respectively (P<0.05). These results may contribute to better understanding the HUFA biosynthetic pathway and regulation mechanism in this species.

Transcriptome analysis of mud crab (Scylla paramamosain) gills in response to Mud crab reovirus (MCRV)

Mud crab (Scylla paramamosain) is an economically important marine cultured species in China's coastal area. Mud crab reovirus (MCRV) is the most important pathogen of mud crab, resulting in large economic losses in crab farming. In this paper, next-generation sequencing technology and bioinformatics analysis are used to study transcriptome differences between MCRV-infected mud crab and normal control. A total of 104.3 million clean reads were obtained, including 52.7 million and 51.6 million clean reads from MCRV-infected (CA) and controlled (HA) mud crabs respectively. 81,901, 70,059 and 67,279 unigenes were gained respectively from HA reads, CA reads and HA&CA reads. A total of 32,547 unigenes from HA&CA reads called All-Unigenes were matched to at least one database among Nr, Nt, Swiss-prot, COG, GO and KEGG databases. Among these, 13,039, 20,260 and 11,866 unigenes belonged to the 3, 258 and 25 categories of GO, KEGG pathway, and COG databases, respectively. Solexa/Illumina's DGE platform was also used, and about 13,856 differentially expressed genes (DEGs), including 4444 significantly upregulated and 9412 downregulated DEGs were detected in diseased crabs compared with the control. KEGG pathway analysis revealed that DEGs were obviously enriched in the pathways related to different diseases or infections. This transcriptome analysis provided valuable information on gene functions associated with the response to MCRV in mud crab, as well as detail information for identifying novel genes in the absence of the mud crab genome database.

Report of leucine-rich repeats (LRRs) from Scylla serrata: Ontogeny, molecular cloning, characterization and expression analysis following ligand stimulation, and upon bacterial and viral infections

Leucine-rich repeat (LRR) proteins are present in all living organisms, and their participation in signal transduction and defense mechanisms has been elucidated in humans and mosquitoes. LRRs possibly involve in protein-protein interactions also and show differential expression pattern upon challenge with pathogens. In the present study, a new LRR gene was identified in mud crab, Scylla serrata. LRR gene mRNA levels in different developmental stages and various tissues of S. serrata were analysed. Further, the response of the gene against different ligands, Gram-negative bacterium, and white spot syndrome virus (WSSV) was investigated in vitro and in vivo. Full-length cDNA sequence of S. serrata LRR (SsLRR) was found to be 2290 nucleotide long with an open reading frame of 1893bp. SsLRR encodes for a protein containing 630 deduced amino acids with 17 conserved LRR domains and exhibits significant similarity with crustacean LRRs so that these could be clustered into a branch in the phylogenetic tree. SsLRR mRNA transcripts were detected in all the developmental stages (egg, Zoea1-5, megalopa and crab instar), haemocytes and various tissues such as, stomach, gill, muscle, hepatopancreas, hematopoietic organ, heart, epithelial layer and testis by reverse-transcriptase PCR. SsLRR transcripts in cultured haemocytes showed a 2-fold increase in expression at 1.5 and 12h upon Poly I:C induction. WSSV challenge resulted in significant early up-regulation at 3h in-vitro and late up-regulation at 72h in-vivo. Peptidoglycan (PGN)-induction resulted in marginal up-regulation of SsLRR at timepoints, 6, 12 and 24h (fold change below 1.5) and no significant change in the expression at early timepoints. LPS-stimulation, on the other hand, showed either down-regulation or normal level of expression at all timepoints. However, a delayed 5-fold up-regulation was observed in vivo against Vibrio parahaemolyticus infection at 72hpi. The constitutive expression of the LRR gene in all the early life-stages, and its response to various ligands and to viral challenge suggest the possible role of the LRR in immune defense in mud crab. The result provides additional information which would help in future studies in understanding the innate immune pathways in crustaceans.

The natural diet of the mud crab Scylla olivacea (Herbst, 1896) in Pichavaram mangroves, India

Food and feeding habits of mud crab Scylla olivacea (Herbst, 1896) in Pichavaram mangroves was investigated quantitatively and qualitatively for a period of two years from June 2010 to May 2012. Gut contents from 1737 specimens comprising 843 males and 894 females in the size range between 45 mm and 148 mm were examined. Crustaceans form the predominant food item in a majority of size groups in terms of percentage wet weight and frequency of occurrence, while molluscs showed a preference in few size groups. The other dietary items includes fishes, detritus, mud and sand and miscellaneous. Gut content analysis revealed no significant variation between the quantities of food consumed by both sexes. Feeding intensity was higher in juveniles and subadults of both sexes than that of adults, revealing a greater preference to feed on fast moving prey such as crustaceans and fishes. The results of the present study indicate that S. olivacea in Pichavaram mangroves exhibited a clear preference for crustaceans.

A review of maturation diets for mud crab genus Scylla broodstock: Present research, problems and future perspective

Study of broodstock maturation diets is important in order to increase the quality of berried females, which indirectly improve the larval quantity in the hatchery production of cultured species. This paper reviewed the studies on the maturation diets for mud crab broodstock, genus Scylla and compared independently to identify their effect on reproductive performance and larval quality. The broodstock is usually caught from the wild and held in the spawning or maturation tank for further use of hatchery seed production. Mud crab broodstock was fed either natural diet, artificial diet or mixed diet. Trash fishes were commonly used as a natural feed for mud crab broodstock; meanwhile artificial diets are from formulated fish meal and various kinds of feed. The results indicated that mud crab broodstock has a high dietary requirement for lipids, fatty acids and protein which are to be used during the maturation and breeding processes. However, the natural diet produce better larval quality compared to the artificial diet. The mixed diet is the better diet which resulted in better reproductive performances such as growth, survival, fecundity and maturation processes. This review also discusses the problems in the previous studies for the potential future research to develop very high quality and cost-effective formulated diet for the enhancement of broodstock and seed production technology. Information from this review can be useful in developing a better quality of crustacean broodstock’s diet for commercial hatchery production.

Enhancement of the immune response and protection against Vibrio parahaemolyticus by indigenous probiotic Bacillus strains in mud crab (Scylla paramamosain)

In a previous study, bacterial communities of the intestine in three populations of crabs (wild crabs, pond-raised healthy crabs and diseased crabs) were probed by culture-independent methods. In this study, we examined the intestinal communities of the crabs by bacterial cultivation with a variety of media. A total of 135 bacterial strains were isolated from three populations of mud crabs. The strains were screened for antagonistic activity against Vibrio parahaemolyticus using an agar spot assay. Antagonistic strains were then identified by 16S rRNA gene sequence analysis. Three strains (Bacillus subtilis DCU, Bacillus pumilus BP, Bacillus cereus HL7) with the strongest antagonistic activity were further evaluated for their probiotic characteristics. The results showed that two (BP and DCU) of them were able to survive low pH and high bile concentrations, showed good adherence characteristics and a broad spectrum of antibiotic resistance. The probiotic effects were then tested by feeding juvenile mud crabs (Scylla paramamosain) with foods supplemented with 10(5) CFU/g of BP or DCU for 30 days before being subjected to an immersion challenge with V. parahaemolyticus for 48 h. The treated crabs showed significantly higher expression levels of immune related genes (CAT, proPO and SOD) and activities of respiratory burst than that in controlled groups. Crabs treated with BP and DCU supplemented diets exhibited survival rates of 76.67% and 78.33%, respectively, whereas survival rate was 54.88% in crabs not treated with the probiotics. The data showed that indigenous mud-associated microbiota, such as DCU and BP, have potential application in controlling pathogenic Vibriosis in mud crab aquaculture.

Chitosan extracted from mud crab (Scylla olivicea) shells: physicochemical and antioxidant properties

The aim of this study is to report the yield of extraction, as well as the physicochemical and antioxidant properties of extracted chitosan from mud crabs (S.olivacea) as compared to commercial chitosan. The yield obtained for extracted chitosan was 44.57 ± 3.44 % with a moisture and ash content of 9.48 ± 0.59 % and 5.97 ± 0.90 %, respectively. Commercial chitosan demonstrated a higher degree of deacetylation (58.42 ± 2.67 %), water (250 ± 9.90 %) and fat (329 ± 7.07 %) binding capacity, solubility (73.85 %), viscosity (463.25 ± 13.10 %) and also the whiteness value (77.8 ± 0.47) compared to the extracted chitosan, which were only 53.42 ± 0.88 %, 180 ± 0.00 %, 260 ± 0.00 %, 53.38 %, 383.9 ± 28.43 % and 62.1 ± 7.52 %, respectively. The structure of extracted and commercial chitosan was also investigated using Fourier Transform Infrared Spectroscopy (FTIR). In conclusion, the extracted chitosan possessed potential properties similar to the commercial chitosan with high reducing power but low in the scavenging activity on the DPPH and hydroxyl radicals compared to the commercial chitosan.

Characterization of the circulating hemocytes in mud crab (Scylla olivacea) revealed phenoloxidase activity

This study focused on an isolation and characterization of the circulating hemocytes in mud crab, Scylla olivacea. Isolation of specific cell types of hemocytes from crab hemolymph was accomplished by using 60% Percoll density gradient centrifugation. Four separated bands of the hemocytes were successfully obtained. Characterization of these isolated hemocytes by light microscope using trypan blue-rose bengal staining, rose bengal-hematoxilin staining, and phase contrast revealed four distinct types of hemocyte cells. Using their specific morphology and granularity, they were identified as hyaline cell (HC), small granular cell (SGC), large granular cell (LGC) and mixed granular cell (MGC). Transmission electron microscopy (TEM) revealed more details on specific cell size, size of cytoplasmic granule, and nuclear to cytoplasmic ratio, and confirmed the classification. Relative abundance of these cells types in the hemolymph of an adult crab were 15.50±8.22% for HC, 55.50±7.15% for SGC, 13.50±5.28% for LGC, and 15.50±3.50% for MGC. Proteomic analysis of protein expression for each specific cell types by two-dimensional electrophoresis identified two highly abundant proteins, prophenoloxidase (ProPO) and peroxinectin in LGC. Determination of phenoloxidase (PO) activity in each isolated cell types using in vitro and in situ chemical assays confirmed the presence of PO activity only in LGC. Based on an increased PO activity of crab hemolymph during the course of White Spot Syndrome Virus (WSSV) infection, these results suggest that prophenoloxidase pathway was employed for host defense mechanism against WSSV and it may link to the role of large granular hemocyte.