Mud Crab Aquaculture Research Articles

Comparative analysis of embryonic development and growth performance among two mud crab species and their hybrids

In modern aquaculture, inter-specific hybridization enhances traits, but its effects on embryonic development and growth in mud crabs (genus Scylla) remain underexplored. This study investigated the embryonic development and growth performance of Scylla paramamosain, Scylla serrata, and their hybrid offspring from reciprocal crosses. We found that S. paramamosain and the hybrid (S. paramamosain ♀ × S. serrata ♂) produced smaller eggs with shorter development periods than S. serrata and the hybrid (S. serrata ♀ × S. paramamosain ♂). Both hybrids exhibited higher growth rates in the crablet stage than their purebred parents. Notably, the hybrid (S. serrata ♀ × S. paramamosain ♂) demonstrated significant heterosis in body weight and height, while the hybrid (S. paramamosain ♀ × S. serrata ♂) showed single-parent heterosis. While the shape of the frontal lobe spines in hybrids depended on the male parent. Development durations varied, with the longest observed in the hybrid (S. paramamosain ♂ × S. serrata ♀). Discriminant analysis of growth traits showed high accuracy across developmental stages, supporting the potential of inter-specific hybridization for enhancing mud crab aquaculture. This research provides valuable insights and germplasm resources for the aquaculture industry.

Nutritional prospects and heavy metal risks in fattened versus wild mud crabs of the Ganges-Brahmaputra delta: Implications for sustainable management

Scylla olivacea, or the mud crab, is a crucial economic contributor in Southeast Asia, notably in the coastal region of the Ganges-Brahmaputra delta. This study compared the nutritional and heavy metals of fattened and wild-captured mud crabs from the southwest coastal areas of the Ganges-Brahmaputra delta, focusing on proximate composition, fatty acids, amino acids, and heavy metals. Fattened mud crabs showed higher crude protein levels (13.2%–14.4%), particularly in males, and higher crude fat and ash contents than their wild counterparts. Among fatty acids, fattened crabs had the highest palmitic acid levels (34.0%–41.2%), whereas wild crabs were rich in linoleic and linolenic acids. Amino acid analysis revealed that histidine and arginine were the most prevalent essential amino acids in fattened and wild crabs, respectively. Elemental analysis indicated that calcium levels were high in both groups. However, zinc, copper, iron, and manganese concentrations exceeded recommended dietary allowances. Furthermore, the wild mud crabs contained heavy metals lower than that of the fattened mud crabs. Notably, nickel, lead, and cadmium levels surpassed maximum permissible limits, suggesting potential health risks in fattened and wild mud crabs. The concentration of Omega-3 fatty acids was higher in wild crabs than in cultured ones. These findings emphasize the need for cautious consumption and strict monitoring in mud crab aquaculture to ensure food safety and sustainability.

Characteristics and pathogenicity of Vibrio alginolyticus SWS causing high mortality in mud crab (Scylla serrata) aquaculture in Hong Kong.

Vibrio alginolyticus is a Gram-negative, rod-shaped bacterium belonging to the family of Vibrionaceae, a common pathogen in aquaculture animals, However, studies on its impact on Scylla serrata (mud crabs) are limited. In this study, we isolated V. alginolyticus SWS from dead mud crab during a disease outbreak in a Hong Kong aquaculture farm, which caused up to 70% mortality during summer. Experimental infection and histopathology were used to investigate the pathogenicity of V. alginolyticus SWS in S. serrata and validate Koch's postulates. Comprehensive whole-genome analysis and phylogenetic analysis antimicrobial susceptibility testing, and biochemical characterization were also performed. Our findings showed that V. alginolyticus SWS caused high mortality (75%) in S. serrata with infected individuals exhibiting inactivity, loss of appetite, decolored and darkened hepatopancreas, gills, and opaque muscle in the claw. Histopathological analysis revealed tissue damage and degeneration in the hepatopancreas, gills, and claw muscle suggesting direct and indirect impacts of V. alginolyticus SWS infection. This study provides a comprehensive characterization of V. alginolyticus SWS as an emerging pathogen in S. serrata aquaculture. Our findings underscore the importance of ongoing surveillance, early detection, and the development of targeted disease management strategies to mitigate the economic impact of vibriosis outbreaks in mud crab aquaculture.

Impact and accumulation of calcium on soft-shell mud crab Scylla paramamosain in recirculating aquaculture system

Soft-shell crabs are highly valued for their commercial significance and culinary appeal. To enhance production of soft-shell crabs, careful attention should be paid to the water calcium concentration in their culture. This study investigated the influences of different levels of calcium concentrations on the molting and growth of mud crab (Scylla paramamosain) within a meticulously controlled recirculating aquaculture system (RAS). We established three distinct water calcium concentration gradients (200, 300, and 450 mg/L) to comprehensively assess feeding habits, molting patterns, growth, and tissue calcium levels of mud crab. Initially, we observed a gradual reduction in water calcium concentrations with increments of crab molting events in RAS. Throughout one molting cycle, the feeding incidence of the crabs remained consistently high from 4 days to 37 days post-molt, irrespective of different calcium concentrations. Nonetheless, high water calcium levels (300 and 450 mg/L) significantly shortened molt intervals and accelerated exoskeletal calcification. Specifically, the molt intervals were 52.30 ± 2.72 d, 41.65 ± 5.24 d, and 37.70 ± 3.02 d, while the carapace hardening durations were 21.51 ± 4.33 h, 17.23 ± 3.38 h, and 13.46 ± 2.76 h at water calcium concentrations of 200, 300, and 450 mg/L, respectively. Moreover, elevated calcium concentrations also significantly enhanced weight gain of the mud crab during molting. Noteworthy, regardless of fluctuations in water calcium concentration, the condition factor of the molting crabs was approximately 63%, which could be an indicator of crab selection in soft-shell crab cultivation. Furthermore, the dynamic changes in calcium concentrations were disparate among different tissues in the post-molt stage. Gill and exoskeleton tissues exhibited an upward trend in calcium concentrations, while hemolymph and hepatopancreas tissues displayed distinct patterns of decrease followed by increase. Gill and exoskeleton tissues were identified as primary sites for calcium absorption and utilization, evidenced by a positive correlation between high calcium concentrations and increased calcium content in these tissues at 6 h and 3 d post-molt. Overall, our findings provide practical evidence for optimizing aquaculture management strategies through adjustments in water calcium concentration, thus to enhance production efficiency and profitability in soft-shell mud crab aquaculture.

Identification and Characterization of a Potential Probiotic, Clostridium butyricum G13, Isolated from the Intestine of the Mud Crab (Scylla paramamosain).

The butyrate-producing bacterium Clostridium butyricum has been proven to be important in improving the growth and health benefits of aquatic animals. In this study, C. butyricum G13 was isolated for the first time from the gut of the mud crab (Scylla paramamosain). The results of this study showed that C. butyricum G13 could produce a high concentration of butyric acid and grow well in a wide range of pHs (4 to 9) and NaCl (1 to 2.5%) and bile salt (0.2 to 1.0%) concentrations. In vitro characterization revealed that C. butyricum G13 is a Gram-positive and gamma-hemolytic bacterium sensitive to most antibiotics and shows hydrophobicity and the capacity to degrade starch. In vitro fermentation using mud crab gut contents showed that C. butyricum G13 alone or in combination with galactooligosaccharides (GOS) and/or resistant starch (RS) significantly increased butyric acid production and beneficially affected the abundance and diversity of intestinal microbiota. In addition, C. butyricum G13 can improve the survival rate of mud crabs and effectively maintain the normal structure of gut morphology after infection with Vibrio parahaemolyticus. In conclusion, C. butyricum G13 can be considered a potential probiotic that improves the immune capacity and confers health benefits on mud crabs. IMPORTANCE With the development of society, more and more aquatic animals are demanded. Intensification in the aquaculture scale is facing problems, such as disease outbreaks, eutrophication of water bodies, and misuse of antibiotics. Among these challenges, disease outbreak is the most important factor directly affecting aquaculture production. It is crucial to explore new approaches effective for the prevention and control of diseases. Probiotics have been widely used in aquaculture and have shown beneficial effects on the host. In this study, the butyrate-producing bacterium Clostridium butyricum G13 was isolated for the first time from the intestine of the mud crab through in vitro fermentation. The bacterium has probiotic properties and changes the gut microbiota to be beneficial to hosts in vitro as well as protecting hosts from Vibrio parahaemolyticus infection in vivo. The outcomes of this study indicate that C. butyricum G13 can be used as a potential probiotic in mud crab aquaculture.

Challenges and opportunities in achieving sustainable mud crab aquaculture in tropical coastal regions

Aquaculture plays a significant role in food security and provides livelihoods and employment for millions of people among coastal communities worldwide. However, the growing aquaculture sector has also created debates around its long-term ecological sustainability, economic viability, potential social inequalities and governance issues. We investigated the perceived challenges and opportunities to achieving sustainable mud crab aquaculture in tropical coastal regions by using the case study of coastal mud crab farms in Andhra Pradesh, India. Informed by perceptions and indicative financial data from a sample of stakeholders we investigated the potential economic outcomes under different scenarios representing varying yield levels, risk factors and project time periods. The main risks identified by the stakeholders were associated with the limited supply of mud crab seeds and the lack of access to governmental and non-governmental support schemes. There are no financial buffers, therefore major disease outbreaks or extreme weather conditions caused by climate change would lead to a loss of livelihoods. This paper also highlights the most critical factor determining the level of success of mud crab farming being the crab survival rate which is influenced by a variety of factors including increasing sea surface temperature. The results of this study show that small-scale mud crab farming has fewer risks and higher flexibility involved than large-scale mud crab farming. It could be an economically sustainable enterprise and serve as a tool for poverty alleviation in developing countries if microfinance support and training are available.

Mud Crab Culture in the Coastal Brackish Water Wetlands of West Bengal – A Promising Enterprise

Mud crab culture or crab fattening in brackish water wetlands of coastal West Bengal locally known as Chamber chas was initiated in the Sundarban coast since 1990s. Two species, viz., Scylla serrata and Scylla tranquebarica are reared in small and medium sized brackish water ponds for a period of about 18 days, using undersized and discarded crabs, mainly with help of household manpower to earn their living in this region. This is briefly reviewed herein to highlight the crab fattening enterprise and to promote the mud crab aquaculture so that the dependency on capture fishing may be reduced especially from mangrove tigerland of Sundarban, West Bengal.

Studies on Diversity of Bacterial Diseases and Occupational Risks through Mudcrab Aquaculture in West Bengal

In West Bengal, the two most tradable species of mud crab (Scylla sp.) are available due to high market demand in local as well as foreign markets. Scylla sp. is an important (ecological, nutritional, and economical) bioresource in India including West Bengal. Juveniles and adult mud crabs are selectively collected by coastal area common people or fisherpersons for culturing in ponds and crabs are traded locally or internationally. Different coastal districts’ people of West Bengal, mainly North-24 Parganas, South-24 Parganas, and Midnapur are inextricably linked to the crab as being culture that serves as their alternative occupation/livelihood. Various bacteria are recorded as related to mud crab as being infections. Some of the bacteria may transmit from mud crabs to humans and cause mainly gastric-related diseases and septicemia by the transmission of virulent genes and microbes from unsafe water to the crab and then to humans. Such pathogenic infections like vibriosis without proper treatment can result in mass mortality of Scylla sp. The potential for disease transmission to people from mud crabs has been demonstrated by a number of significant variables and the water surrounding them. Eating raw or undercooked crab, ingesting water or other substances contaminated with infected crab excrement or mucus, and coming into touch with the infectious agent through open wounds or contact skin scratches or abrasions are the main sources of bacterial infections. It is reported that bacteria transferred by consuming contaminated water with infected organisms or handling are more than 10%. Crab fisherpersons and farmers, in general, have less environmental awareness, and scientific-based knowledge and for this reason, they face various types of occupational hazards including zoonotic septicemia. The present article investigates the distribution of different zoonotic bacteria and their potential threats, both for mud crabs and the human population.

Microplastics pollution in mud crab (Scylla sp.) aquaculture system: First investigation and evidence

Microplastics (MPs) occurrence in farmed aquatic organisms has already been the prime priority of researchers due to the food security concerns for human consumption. A number of commercially important aquaculture systems have already been investigated for MPs pollution but the mud crab (Scylla sp.) aquaculture system has not been investigated yet even though it is a highly demanded commercial species globally. This study reported the MPs pollution in the mud crab (Scylla sp.) aquaculture system for the first time. Three different stations of the selected aquafarm were sampled for water and sediment samples and MPs particles in the samples were isolated by the gravimetric analysis (0.9% w/v NaCl solution). MP abundance was visualized under a microscope along with their size, shape, and color. A subset of the isolated MPs was analyzed by scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR) for the surface and chemical characterization respectively. The average MPs concentration was 47.5 ± 11.875 particles/g in sediment and 127.92 ± 14.99 particles/100 L in the water sample. Fibrous-shaped (72.17%) and transparent-colored (59.37%) MPs were dominant in all the collected samples. However, smaller MPs (>0.05–0.5 mm) were more common in the water samples (47.69%) and the larger (>1–5 mm) MPs were in the sediment samples (47.83%). SEM analysis found cracks and roughness on the surface of the MPs and nylon, polyethylene, polypropylene, and polystyrene MPs were identified by FTIR analysis. PLI value showed hazard level I in water and level II in sediment. The existence of deleterious MPs particles in the mud crab aquaculture system was well evident. The other commercial mud crab aquafarms must therefore be thoroughly investigated in order to include farmed mud crabs as an environmentally vulnerable food security concern.

Population dynamics and reproductive biology of Scylla serrata (Forskål, 1775) on the shores overlooking the mangrove forest of the Persian Gulf

Size frequency distribution and reproductive biology of Scylla serrata (Forskål, 1775) collected by gill net in the tidal zone of the northern Persian Gulf were studied in May 2019 and then from November 2019 to September 2020. A biometric data of 165 mud crabs showed that males are larger compared to females. The populations of male and female crabs were dominated by adult crabs (CW > 100 mm) from winter to mid-spring (December to May). The juvenile crabs were dominant from late spring to mid-summer (May to August). The sex ratio of male:female was 3:1, with 75.2% being male. This species could spawn continuously throughout the year and its peak occurs in winter and spring. The size of the first-maturity of females and LM50% were recorded in the carapace width of 82 mm and 99.4 mm, respectively. The carapace width–weight relationship showed positive allometric growth in male crabs and negative allometric growth in female crabs with a b value calculated to be 3.43 and 2.97 for males and females, respectively.The parameters CW ∞, K, and t0 were estimated at 217 mm, 1.5 Y−1, −0.61 y−1 for males and 198 mm, 1.1 Y−1, −0.86 y−1 for females, respectively. The φ index was estimated at 4.85 in males and 4.63 in females. Total, natural, and fishing mortality rates were estimated at 3.50, 1.32, and 2.18 Y−1 for males and 1.46, 1.10, and 0.36 Y−1 for females, respectively. The exploitation ratio was calculated to be 0.62 for males and 0.24 for females.This findings state of knowledge on the population biology of mud crabs will act as a baseline to propose suitable management strategies for the S. serrata stocks on the Iranian coast as well as for future research to support the development of sustainable mud crab aquaculture and fisheries.

Study on growth, survival and intactness of sub-adult to adult mud crab aquaculture under low saline earthen pondsin the coastal areas of Bangladesh

To assess the growth, survival and intactness of mud crabanexperiment was conducted for a period of 120 days from July to October 2021 in the farmers ponds of Betbunia village under Paikgacha upazilla at Khulna Districts, Bangladesh. The crab Juvenile was collected from adjacent Shibsha River and stocked in a pond of 0.01 ha area with the stocking density at 1 m2,2m2, 3 m2in T1,T2 and T3 treatments with 2 replications each. Fresh choppedtilapiafish was fed and the feed was adjusted periodically in accordance with the growth performance. Production and physico-chemical parameters were recorded and analyzed according to standard methodsduring the culture period. Among these parameters salinity has significant (p<0.05) role on survival of mud crab.After 120 days of rearing, obtained average final weight was 97.8±13.86g, 94.22±9.25gand 117.77±14.34g; with the estimated yield of 371.56 kg/ha, 433.12 kg/ha and 376.56 kg/ha, survival was 38%, 46% and 32% in T1, T2 and T3 treatments respectively.Results and findings of the present study suggested that poor salinity level and cannibalism is the potential constraints inthe growth, survival and intactness of mud crab aquaculturein the coastal areas of Bangladesh.

Mud Crab (Scylla spp.) Aquaculture in the South-West Sundarbans Region of Bangladesh

Mud crab (Scylla spp.) aquaculture has become an important livelihood option for the coastal fisher-folks in Bangladesh. Mud crabs harvested from wild sources are traditionally fattened in pens installed in tidal rivers, ghers, and earthen ponds in Bangladesh. The study was aimed at understanding the practice and production economics of mud crab farming in the South-West Sundarbans region of Bangladesh, and was conducted in the areas namely Bagerhat, Satkhira and Khulna districts where mud crab fattening are predominately ventured. Most of the farmers fatten both male (lean) and female (gonadally immature) crabs of 100 - 180 g. The crabs are stocked at varying rate (12 - 641 g/m2), and fed at the rate of 8-10% of body weight with trash live fishes, dried fishes, snails, mollusks, and cattle viscera. The fattening for a mean cycle of 22 ± 14.34 days has the survival rate of 55 - 90%, and has the production of 0.065 ± 0.26, 0.084 ± 1.33, and 0.17 ± 3.76 kg/m2 in Bagerhat, Satkhira, and Khulna, respectively. After harvesting (mostly partial), crabs are sold at average price rate of 4.35 ± 0.45 US$/kg. The lowest production cost (3.14 US$/kg) and the better economic return (US$ 147.77) per cycle was recorded in the district of Satkhira. The mud crab fattening has hitherto been evaluated economically feasible in and around the Sundarbans region, but the production and economic efficiency can be scaled up adopting scientifically demonstrated regime of stocking, feeding, and health management. The development of crab seed hatchery, artificial feed for crab, and strongest marketing network are addressed as crux issues for the sustainability of mud crab aquaculture in Bangladesh.

A New C-Type Lectin Homolog SpCTL6 Exerting Immunoprotective Effect and Regulatory Role in Mud Crab Scylla paramamosain.

C-type lectin (CTL), a well-known immune-related molecule, has received more and more attention due to its diverse functions, especially its important role in development and host defense of vertebrate and invertebrate. Since the research on crab CTLs is still lack, we screened a new CTL homolog, named SpCTL6 from mud crab Scylla paramamosain. The full-length cDNA sequence of SpCTL6 was 738 bp with a 486 bp of ORF, and the deduced amino acids were 161 aa. SpCTL6 was predicted to have a 17 aa signal peptide and its mature peptide was 144 aa (MW 16.7 kDa) with pI value of 5.22. It had typical CTL structural characteristics, such as a single C-type lectin-like domain, 4 conserved cysteines, similar tertiary structure to that of vertebrate CTLs and a mutated Ca2+ binding motif Gln-Pro-Thr (QPT), clustering into the same branch as the crustacean CTLs. SpCTL6 was highly expressed in the entire zoeal larval stages and widely distributed in adult crab tissues with the highest transcription level in testis. During the molting process of juvenile crabs, the expression level of SpCTL6 was remarkably increased after molting. SpCTL6 could be significantly upregulated in two larval stages (Z1 and megalopa) and adult crab testis under immune challenges. Recombinant SpCTL6 (rSpCTL6) was successfully obtained from eukaryotic expression system. rSpCTL6 exhibited binding activity with PAMPs (LPS, lipoteichoic acid, peptidoglycan, and glucan) and had a broad spectrum bacterial agglutination activity in a Ca2+-dependent manner. In addition, rSpCTL6 could enhance the encapsulation activity of hemocytes and has no cytotoxic effect on hemocytes. Although rSpCTL6 had no bactericidal activity on Vibrio alginolyticus, rSpCTL6 treatment could significantly reduce the bacterial endotoxin level in vitro and greatly improved the survival of S. paramamosain under V. alginolyticus infection in vivo. The immunoprotective effect of rSpCTL6 might be due to the regulatory role of rSpCTL6 in immune-related genes and immunological parameters. Our study provides new information for understanding the immune defense of mud crabs and would facilitate the development of effective strategies for mud crab aquaculture disease control.

Outbreak of vibriosis associated with Vibrio parahaemolyticus in the mud crab Scylla paramamosain cultured in China.

In this study, a Gram-negative bacterium was isolated from diseased Scylla paramamosain and tentatively named strain QX17. The bacterial isolate was identified as Vibrio parahaemolyticus based on morphological and biochemical characteristics and molecular identification with the 16S rRNA and HSP60 genes. In the challenge experiment, S. paramamosain injected intramuscularly with the V. parahaemolyticus isolate developed pathological signs similar to the naturally diseased mud crabs. The infection experiment also showed that the median lethal dosage (LD50) for QX17 was 4.79 × 102 CFU g-1 (crab weight). Histopathological analysis of the diseased mud crabs infected with V. parahaemolyticus showed deformation and basement membrane rupture of hepatopancreatic tubules in the hepatopancreas, and disordered and broken muscle fiber in the muscle. Antimicrobial susceptibility tests revealed that QX17 was highly sensitive to most of the tested aminoglycosides, tetracyclines, and quinolones. To the best of our knowledge, this is the first study reporting isolation and antibiotic sensitivities of V. parahaemolyticus from cultured mud crabs. The discovery of V. parahaemolyticus in cultured mud crabs not only adds to the growing list of emerging pathogens in crab aquaculture in China, but also highlights the necessity of developing early detection strategies and appropriate interventions to reduce the damage caused by V. parahaemolyticus in mud crab aquaculture.

Induced mating of newly molted females of orange mud crab, Scylla olivacea (Herbst, 1796), in captivity

Mud crab aquaculture is gaining attention in tropical and sub-tropical regions for its high commercial value. Mating is the fundamental requirement for the natural seed production of mud crabs. The aim of this study was to develop an induced mating technique of orange mud crab, Scylla olivacea in captivity to support sustainable mud crab farming through increasing the supply of hatchery-produced mud crab seeds. Induced mating technique involved the mating of a mature induced soft-shelled female (newly molted) with a mature intermolt male. The mating pairs were selected randomly. This study proved that S. olivacea can copulate without pre-copulation (pairing of male-female before copulation) and post-copulatory guarding by the male. Spermatophores were found in the seminal receptacles of all the copulated females. A mating success of 83.33 ± 5.77% was obtained in captivity using this technique, and can be applied in future breeding and hybridization trials of mud crabs.

First report of Photobacterium damselae subsp. damselae infection in the mud crab Scylla paramamosain cultured in China

In May 2017, there was a massive mortality of mud crab Scylla paramamosain in a farm of Sanmen, Zhejiang Province, China. The bacterial isolates from the hepatopancreas and muscle of the diseased S. paramamosain showed the same phenotypic traits and biochemical profiles, and were identified as Photobacterium damselae subsp. damselae in accordance with the biochemical characteristics and molecular identification with the 16S rRNA and ureC genes. The morphological observation suggested that P. damselae subsp. damselae QX175062 strain was a rod-shaped bacterium with singlet flagellum. Bacterial infection tests were conducted by intramuscular injection of the QX175062 isolate into healthy mud crabs, and the results indicated that the isolate was lethal to S. paramamosain with the LD50 value of 3.63 × 101 CFU/g (body weight). The challenged mud crabs showed similar pathological signs as those that were naturally infected. Histopathological analysis of mud crabs injected with QX175062 isolate showed agglutination and necrosis of hepatopancreatic tubules in hepatopancreas; ruptured or disordered tissue and fiber dissolution in muscle. Antibiogram study revealed that QX175062 isolate was mainly sensitive to tetracyclines, aminoglycosides, macrolides and quinolones, but resistant to β-lactam antibiotic drugs. This first case report underlines the involvement of P. damselae subsp. damselae in the mud crab aquaculture with disease outbreak and emphasizes the need of developing rapid diagnostic methods and prevention measures to reduce the economic loss caused by P. damselae subsp. damselae infection in mud crab aquaculture.

A Possible Role of Crustacean Cardioactive Peptide in Regulating Immune Response in Hepatopancreas of Mud Crab

Crustacean cardioactive peptide (CCAP), a cyclic amidated non-apeptide, is widely found in arthropods. The functions of CCAP have been revealed to include regulation of heart rate, intestinal peristalsis, molting, and osmotic pressure. However, to date, there has not been any report on the possible involvement of CCAP in immunoregulation in crustaceans. In this study, a CCAP precursor (designated as Sp-CCAP) was identified in the commercially important mud crab Scylla paramamosain, which could be processed into four CCAP-associated peptides and one mature peptide (PFCNAFTGC-NH2). Bioinformatics analysis indicated that Sp-CCAP was highly conserved in crustaceans. RT-PCR results revealed that Sp-CCAP was expressed in nerve tissues and gonads, whereas the Sp-CCAP receptor gene (Sp-CCAPR) was expressed in 12 tissues of S. paramamosain, including hepatopancreas. In situ hybridization further showed that an Sp-CCAPR-positive signal is mainly localized in the F-cells of hepatopancreas. Moreover, the mRNA expression level of Sp-CCAPR in the hepatopancreas was significantly up-regulated after lipopolysaccharide (LPS) or polyriboinosinic polyribocytidylic acid [Poly (I:C)] challenge. Meanwhile, the mRNA expression level of Sp-CCAPR, nuclear transcription factor NF-κB homologs (Sp-Dorsal and Sp-Relish), member of mitogen-activated protein kinase (MAPK) signaling pathway (Sp-P38), pro-inflammatory cytokines factor (Sp-TNFSF and Sp-IL16), and antimicrobial peptide (Sp-Lysozyme, Sp-ALF, Sp-ALF4, and Sp-ALF5) in the hepatopancreas were all up-regulated after the administration of synthetic Sp-CCAP mature peptide both in vivo and in vitro. The addition of synthetic Sp-CCAP mature peptide in vitro also led to an increase in nitric oxide (NO) concentration and an improved bacterial clearance ability in the hepatopancreas culture medium. The present study suggested that Sp-CCAP signaling system might be involved in the immune responses of S. paramamosain by activating immune molecules on the hepatopancreas. Collectively, our findings shed new light on neuroendocrine-immune regulatory system in arthropods and could potentially provide a new strategy for disease prevention and control for mud crab aquaculture.

Short neuropeptide F enhances the immune response in the hepatopancreas of mud crab (Scylla paramamosain)

Short neuropeptide F (sNPF), a highly conserved neuropeptide, displays pleiotropic functions on multiple aspects of physiological processes, such as feeding, metabolic stress, locomotion, circadian clock and reproduction. However, to date there has no any report on the possible immunoregulation of sNPF in crustaceans. In the present study, we found that the Sp-sNPF was mainly expressed in the nervous tissue in the mud crab Scylla paramamosain, while the sNPF receptor gene (Sp-sNPF-R) was expressed in a wide variety of tissues, including the hepatopancreas. In situ hybridization further showed that the Sp-sNPF-R positive signal mainly localized in the F-cells of the hepatopancreas. Moreover, the Sp-sNPF-R transcription could be significantly up-regulated after the challenge of bacteria-analog LPS or virus-analog Poly (I:C). Both in vitro and in vivo experiments showed that the synthetic sNPF peptide significantly increased the gene expressions of sNPF-R, nuclear factor-κB (NF-κB) signaling genes and antimicrobial peptides (AMPs) in the hepatopancreas. Simultaneously, the administration of sNPF peptide in vitro also increased the concentration of nitric oxide (NO) and the bacteriostasis of the culture medium of hepatopancreas. These results indicated that sNPF up-regulated hepatopancreas immune responses, which may bring new insight into the neuroendocrine-immune regulatory system in crustacean species, and could potentially provide a new strategy for disease prevention and control for mud crab aquaculture.

Mud crab fishery in climate vulnerable coastal Bangladesh: an analysis towards sustainable development

Developing countries are far more vulnerable to climate change impacts than industrialised countries. Most of the world’s poor live in South Asia where they have limited livelihood options that have become even narrower in recent years, indicating a need for alternative income-generating options. Mud crabs (Scylla spp.) are considered to have promising prospects in different parts of the world including Bangladesh, a well-known region for its vulnerability to climate change. At present, this fishery has become a growing venture in coastal Bangladesh, primarily due to the potential of the export market and availability of seed locally. This study included a calculation of the Human Development Index linked to mud crab fishery (HDIMCF) and a strengths, weaknesses, opportunities and threats (SWOT) analysis to clarify the present status of and strategic directions for the mud crab fishery, for the first time. Results revealed an intermediate level of development of mud crab aquaculture, indicating potential alternative livelihood opportunities for vulnerable coastal communities. The SWOT analysis revealed that positive factors, both internal (strengths) and external (opportunities), predominate over negative factors (weaknesses and threats) and that the fishery can be an alternative livelihood option for vulnerable coastal communities. Despite noticeable diversification of the mud crab fishery, dependence on wild seedstock and possible over-exploitation in the wild appear to constrain sustainable development of the fishery. This study’s findings suggest undertaking immediate wild crab stock assessment for determining current status of wild populations. Moreover, modification of the Government of Bangladesh’s existing mud crab policy is needed to better meet growing demand and sustainability of the fishery. Recommendations of this study may be of help in guiding responsible integrated coastal fisheries management and policy.

Innate immune responses and metabolic alterations of mud crab (Scylla paramamosain) in response to Vibrio parahaemolyticus infection

Vibrio parahaemolyticus is one of the major pathogens caused diseases in cultured mud crab (Scylla paramamosain). Mud crabs lack an adaptive immune system, their defenses depend almost on innate immunity. Evaluation of the molecular responses of mud crabs to pathogens is essential for control of disease occurrence in farmed animals. In this study, the impacts of V. parahaemolyticus on immunity-related genes and metabolites in mud crabs of different groups (PG, SG and MG refer to controlled, survival and moribund groups, respectively) were investigated. Our results revealed that V. parahaemolyticus infection stimulated significant expressions of immune-related genes (prophenoloxidase, alpha 2-macroglobulin, lysosomal-associated membrane protein, Rab5, C-type lectin B and anti-lipopolysaccharide factor 5) in the MG within 72 h post-infection. The ATP content was significantly reduced in all tissues except muscle of moribund mud crabs. A total of 668 metabolites (including 190 down-regulated and 145 up-regulated) were identified and assigned to 77 pathways in both SG and MG. Metabolites involved in the saturated fatty acid are up-regulated, whereas unsaturated fatty acid and amino acid metabolisms are down-regulated in the immune system of mud crabs during the bacterial infection in MG. Furthermore, a reduction of hemocyte number and an increase of microbial abundance was found in MG. Our results demonstrated that V. parahaemolyticus induced death of mud crabs through reducing the metabolites associate with energy biosynthesis and innate immune system (i.e. proliferation of hemocyte and melanization), resulting in decrease of ATP in different tissues and failed to clearance of pathogens, respectively. The findings of this study provide a basic information of the responses of mud crab on bacterial infection, which is essential for prevention and control of diseases in mud crab aquaculture.