Isolation of an Insulin-Like Receptor Involved in the Testicular Development of the Mud Crab Scylla paramamosain

Insulin-like androgenic gland hormone (IAG) is a key regulator of male sexual differentiation in crustaceans that plays important roles in secondary sexual characteristics and testicular development. As a hormone, IAG interacts with its membrane receptor to initiate downstream signal pathways to exert its biological functions. In this study, we isolated a full-length cDNA of an insulin-like receptor (Sp-IR) from the mud crab Scylla paramamosain. Sequence analysis revealed that this receptor consists of a Fu domain, two L domains, three FN-III domains, a transmembrane domain, and a tyrosine kinase domain, classifying it as a member of the tyrosine kinase insulin-like receptors family. Our results also suggested that Sp-IR was highly expressed in the testis and AG in males. Its expression in the testis peaked in stage I but significantly decreased in stages II and III (p < 0.01). Next, both short- and long-term RNA interference (RNAi) experiments were performed on males in stage I to explore Sp-IR function in mud crabs. The results showed that Sp-vasa and Sp-Dsx expression levels in the testis were significantly down-regulated after the specific knockdown of Sp-IR by RNAi. Additionally, the long-term knockdown of Sp-IR led to a considerable decrease in the volume of seminiferous tubules, accompanied by large vacuoles and a reduced production of secondary spermatocytes and spermatids. In conclusion, our results indicated that Sp-IR is involved in testicular development and plays a crucial role in transitioning from primary to secondary spermatocytes. This study provided a molecular basis for the subsequent analysis of the mechanism on male sexual differentiation in Brachyuran crabs.

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.

Consumer Preferences and Willingness to Pay for Mud Crabs in Southeast Asian Countries: A Discrete Choice Experiment

The mud crab (Scylla serrata) is an economically important species found in the mangroves and estuaries of tropical countries and is a popular seafood product in the coastal areas of Southeast Asian markets. The aim of this study is to identify factors affecting consumer preference of mud crabs, and to understand consumers’ willingness to pay (WTP) for these factors in a Singapore market where imported mud crabs from other Asian countries are sold. The results showed that the country of origin matters to participants, affecting purchasing decisions, and consumers were willing to pay approximately 16.48 SGD (11.49 USD, the average price of four shops: 35.55 USD/kg for one mud crab) more if the mud crabs were from Sri Lanka if compared with Indonesian or Cambodian mud crabs. Moreover, consumers were willing to pay 25.08 SGD (17.48 USD) more if the mud crabs were alive and 13.40 SGD (9.34 USD) less if the mud crabs were frozen compared with fresh, but not alive, mud crabs. Furthermore, consumers’ preference in mud crab was associated with the consumers’ religion. Some groups of consumers preferred female mud crabs with eggs over male mud crabs, while other groups preferred male crabs. The results identified diverse consumer preference of mud crabs and, therefore, could provide new insights that are useful for sustainable consumption of mud crabs in the region.

Molting Alters the Microbiome, Immune Response, and Digestive Enzyme Activity in Mud Crab (Scylla paramamosain)

Molting is a crucial lifelong process in the growth, development, and reproduction of crustaceans. In mud crab (Scylla paramamosain), new exoskeleton, gills, and appendages are formed after a molting, which contributes to a 40 to 90% increase in body weight. However, little is currently known about the associations between molting and the dynamic changes of microbiota and physiological characteristics in mud crabs. In this study, the effects of molting on changes of the microbiome, immune response, and digestive enzyme activities in mud crabs were investigated. The results showed dynamic changes in the abundances and community compositions of crab-associated microbiota harboring the gills, subcuticular epidermis, hepatopancreas, midgut, and hemolymph during molting. Renewed microbiota was observed in the gills and midgut of crabs at the postmolt stages, which seems to be related to the formation of a new exoskeleton after the molting. A significant positive correlation between the expression of two antimicrobial peptide (AMP) genes (SpALF5 and SpCrustin) and the relative abundance of two predominant microorganisms (Halomonas and Shewanella) in hemolymph was observed in the whole molt cycle, suggesting that AMPs play a role in modulating hemolymph microbiota. Furthermore, digestive enzymes might play a vital role in the changes of microbiota harboring the hepatopancreas and midgut, which provide suitable conditions for restoring and reconstructing host-microbiome homeostasis during molting. In conclusion, this study confirms that molting affects host-associated microbiota and further sheds light on the effects on the immune response and the digestive systems as well. IMPORTANCE Molting is crucial for crustaceans. In mud crab, its exoskeleton is renewed periodically during molting, and this process is an ideal model to study the effects of host development on its microbiota. Here, multiple approaches were used to investigate the changes in microbial taxa, immune response, and digestive enzyme activity with respect to molting in mud crab. The results found that a renewed microbiota was generated in the gills and midgut of crab after a molt. A significant positive correlation between changes in the relative abundances of microbes (such as Halomonas and Shewanella) and the expression of AMP genes (SpALF5 and SpCrustin) was observed in the hemolymph of crabs during the whole molt cycle, suggesting the modulation of hemolymph microbes by AMPs. Furthermore, the digestive enzymes were found to participate in the regulation of microbiota in hepatopancreas and midgut, consequently providing a suitable condition for the restoration and reconstruction of host-microbiome homeostasis during the molting. This study confirms that molting affects the microbial communities and concomitantly influences the immune and digestive systems in mud crabs. This is also the first time the homeostasis of the host and microbiome, and the associations between molting and physiological characteristics in crustaceans, have been revealed.

dLp/HDL-BGBP and MTP Cloning and Expression Profiles During Embryonic Development in the Mud Crab Scylla paramamosain

Lipids are the main energy source for embryonic development in oviparous animals. Prior to the utilization and catabolism, lipids are primarily transported from the yolk sac to embryonic tissues. In the present study, cDNA encoding a circulatory large lipid transfer protein (LLTP) superfamily member, the precursor of large discoidal lipoprotein (dLp) and high-density lipoprotein/β-1,3-glucan-binding protein (HDL-BGBP), named dLp/HDL-BGBP of 14,787 bp in length, was cloned from the mud crab Scylla paramamosain. dLp/HDL-BGBP was predicted to encode a 4,831 amino acids (aa) protein that was the precursor of dLp and HDL-BGBP, which were both detected in hemolymph by liquid chromatography–mass spectrometry (LC-MS/MS) analysis. For the intracellular LLTP, three microsomal triglyceride transfer protein (MTP) cDNAs of 2,905, 2,897, and 3,088 bp in length were cloned from the mud crab and were predicted to encode MTP-A of 881 aa, MTP-B of 889 aa, and MTP-C of 919 aa, respectively, which were different merely in the N-terminal region and shared an identical sequence of 866 aa. During embryonic development, the expression level of dLp/HDL-BGBP consecutively increased from the early appendage formation stage to the eye pigment-formation stage, which indicated that HDL-BGBP is probably the scaffolding protein for yolk lipid. For the MTP gene, MTP-C accounted for ~70% of MTP mRNA from the blastocyst stage to the nauplius stage, as well as the pre-hatching stage; MTP-C and MTP-A expression levels were comparable from the early appendage formation stage to the late eye pigment-formation stage; MTP-A was extremely low in blastocyst and gastrula stages; MTP-B was expressed at a relatively low-level throughout embryo development. The variations in the expression profiles among MTP transcripts suggested that MTP might play roles in the lipid droplet maturation and lipoprotein assembly during embryonic development.

A Review of the Nursery Culture of Mud Crabs, Genus Scylla: Current Progress and Future Directions

Simple Summary

Nursery culture knowledge is important for successful commercial seed production especially for mud crab, genus Scylla, a highly valued delicacy. The aim of this review paper is to summarise the status and information on the current nursery culture stage of the mud crab. Various aspects of mud crab hatchery described in this paper are expected to facilitate practitioners and lay people to easily understand a mud crab nursery. This review also provides guidelines for researchers in conducting future research and development on a mud crab nursery in order to increase the production of mud crab crablets for the farming industry.

Abstract

The nursery stages of mud crab, genus Scylla, proceed from the megalopa stage to crablet instar stages. We review the definition and several of the key stages in mud crab nursery activities. The practice of the direct stocking of megalopa into ponds is not recommended due to their sensitivity. Instead, nursery rearing is needed to grow-out mud crabs of a larger size before pond stocking. Individual nursery rearing results in a higher survival rate at the expense of growth and a more complicated maintenance process compared with communal rearing. The nursery of mud crabs can be done both indoors or outdoors with adequate shelter and feed required to obtain a good survival percentage and growth performance. Artemia nauplii are still irreplaceable as nursery feed, particularly at the megalopa stage, while the survival rate may be improved if live feed is combined with artificial feed such as microbound diet formulations. Water quality parameters, identical to those proposed in tiger shrimp cultures, can be implemented in mud crab rearing. The transportation of crablets between different locations can be done with or without water. The provision of monosex seeds from mud crab hatcheries is expected to become commonplace, increasing seed price and thus improving the income of farmers. Numerous aspects of a mud crab nursery including nutrition; feeding strategies; understanding their behaviour, i.e., cannibalism; control of environmental factors and practical rearing techniques still need further improvement.

Genetic differentiation and signatures of local adaptation revealed by RADseq for a highly dispersive mud crab Scylla olivacea (Herbst, 1796) in the Sulu Sea

Connectivity of marine populations is shaped by complex interactions between biological and physical processes across the seascape. The influence of environmental features on the genetic structure of populations has key implications for the dynamics and persistence of populations, and an understanding of spatial scales and patterns of connectivity is crucial for management and conservation. This study employed a seascape genomics approach combining larval dispersal modeling and population genomic analysis using single nucleotide polymorphisms (SNPs) obtained from RADseq to examine environmental factors influencing patterns of genetic structure and connectivity for a highly dispersive mud crab Scylla olivacea (Herbst, 1796) in the Sulu Sea. Dispersal simulations reveal widespread but asymmetric larval dispersal influenced by persistent southward and westward surface circulation features in the Sulu Sea. Despite potential for widespread dispersal across the Sulu Sea, significant genetic differentiation was detected among eight populations based on 1,655 SNPs (FST  = 0.0057, p < .001) and a subset of 1,643 putatively neutral SNP markers (FST  = 0.0042, p < .001). Oceanography influences genetic structure, with redundancy analysis (RDA) indicating significant contribution of asymmetric ocean currents to neutral genetic variation ( R adj 2  = 0.133, p = .035). Genetic structure may also reflect demographic factors, with divergent populations characterized by low effective population sizes (N e < 50). Pronounced latitudinal genetic structure was recovered for loci putatively under selection (FST  = 0.2390, p < .001), significantly correlated with sea surface temperature variabilities during peak spawning months for S. olivacea ( R adj 2  = 0.692-0.763; p < .050), suggesting putative signatures of selection and local adaptation to thermal clines. While oceanography and dispersal ability likely shape patterns of gene flow and genetic structure of S. olivacea across the Sulu Sea, the impacts of genetic drift and natural selection influenced by sea surface temperature also appear as likely drivers of population genetic structure. This study contributes to the growing body of literature documenting population genetic structure and local adaptation for highly dispersive marine species, and provides information useful for spatial management of the fishery resource.

Comparative analysis of the intestinal bacterial communities in mud crab Scylla serrata in South India

Little is known about the functions of the crustacean gut microbiome, but environmental parameters and habitat are known to affect the composition of the intestinal microbiome, which may in turn affect the physiological status of the host. The mud crab Scylla serrata is an economically important species, and is wild‐caught, and farmed across the Indo‐Pacific region. In this study, we compared the composition of the gut microbiome (in terms of gut microbial species richness and abundance) of S. serrata collected from wild sites, and farms, from the east and west coast of India, and also tested the effects of the environment on the composition. The water temperature had a statistically significant effect on gut microbiome composition, with microbial biodiversity decreasing with increasing water temperature. This could have negative effects on both wild and farmed mud crabs under future climate change conditions, although further research into the effects of temperature on gut microbiomes is required. By comparison, salinity, crab mass and carapace width, geographical location as well as whether they were farmed or wild‐caught crabs did not have a significant impact on gut microbiome composition. The results indicate that farming does not significantly alter the composition of the gut microbiome when compared to wild‐caught crabs.

Thermal Tolerance and Physiological Changes in Mud Crab, Scylla paramamosain Crablet at Different Water Temperatures

Simple Summary

The nursery phase of mud crab (Scylla spp.)—from megalopa to several, further crablet stagesneeds to be carried out in optimal environmental conditions, until they reach a larger size suitable to being stocked to a pond. This study observed the behavioral thermoregulation of crablet instar phases, and determined the effects of several levels of water temperature on growth, survival, molting cycle, gill condition, and sex ratio in the nursery phase of S. paramamosain. In this study, optimal temperature for the long-term nursery phase of S. paramamosain, beginning with megalopa stage, was found to be 28 to 30 °C, with the possibility that water temperature could affect the sex ratio of mud crabs. Findings of this study could result in increased crablet production from hatcheries, and assist in realizing potential of monosex seed production of S. paramamosain, through temperature treatment.

Abstract

This study was carried out to determine the physiological changes (survival, growth, molting cycle, sex differentiation, and gill condition) of mud crab, Scylla paramamosain crablet at different water temperatures of 24, 28 and 32 °C, and ambient temperature of 27 to 30 °C. Thermoregulatory behavior, represented by preferred temperature (29.83 ± SD 2.47 °C), critical thermal minimum (17.33 ± SD 0.58 °C), critical thermal maximum (40 ± SD 0.00 °C), and thermal tolerance interval (22.67 ± SD 0.58 °C), were checked for Crablet 1 stage only (with ambient temperature as acclimation temperature).Both low (24 °C) and high (32 °C) temperatures were associated with lower growth performance, and survival rate (p < 0.05), in comparison with both 28 °C and ambient temperature treatments.Male ratio at low temperaturetreatment (24 °C) was higher (80.09 ± SD 18.86%) than for other treatments (p < 0.05), observed as 44.81 ± D 10.50%, 41.94 ± SD 19.44%, and 76.30 ± SD 5.13% for 28 °C, 32 °C and ambient temperature treatments, respectively. However, there was no significant difference observed between 24 °C, 28 °C, and ambient temperature treatments. Anatomical alterations of gill lamellae of S. paramamosain crablet for both 32 °C, and 24 °C treatments, appeared thinner and paler than at both 28 °C, and ambient temperature treatments. Based on this study, temperature of 28 to 30 °C was recommended as the optimal temperature for the long-term nursery phase of S. paramamosain.

Characterization of Aquimarina hainanensis isolated from diseased mud crab Scylla serrata larvae in a hatchery

Mass mortality due to necrosis signs occurred in hatchery-reared zoea stage larvae of the mud crab Scylla serrata in Okinawa, Japan, and a causative bacterium was isolated. In this study, we identified and characterized the bacterium by genome analysis, biochemical properties and pathogenicity. The bacterium was a Gram-negative, non-motile, long rod, forming yellow colonies on a marine agar plate. It grew at 20-33°C (not at 37°C) and degraded chitin and gelatin. Phylogenetic analysis of the 16S rRNA gene sequence identified the bacterium as Aquimarina hainanensis. Genome sequence data obtained from Illumina MiSeq generated 29 contigs with 3.56 Mbp in total length and a G + C content of 32.5%. The predicted 16 chitinase genes, as putative virulence factors, had certain homologies with those of genus Aquimarina. Experimental infection with the bacterium conducted on larvae of four crustacean species, brine shrimp Artemia franciscana, freshwater shrimp Caridina multidentata, swimming crab Portunus trituberculatus and mud crab S. serrata, revealed that this bacterium was highly virulent to these species. The present study suggests that the bacterium caused mass mortality in mud crab seed production was A. hainanensis and can be widely pathogenic to crustaceans.

Two Elongases, Elovl4 and Elovl6, Fulfill the Elongation Routes of the LC-PUFA Biosynthesis Pathway in the Orange Mud Crab (Scylla olivacea)

While the capacity for long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis has been elucidated in vertebrates and several invertebrate phyla, the comparative knowledge in crustaceans remains vague. A key obstacle in mapping the full spectrum of LC-PUFA biosynthesis in crustacean is the limited evidence of the functional activities of enzymes involved in desaturation or elongation of polyunsaturated fatty acid substrates. In this present study, we report on the cloning and functional characterization of two Elovl elongases from the orange mud crab, Scylla olivacea. Sequence and phylogenetic analysis suggest these two Elovl as putative Elovl4 and Elovl6, respectively. Using the recombinant expression system in Saccharomyces cerevisiae, we demonstrate the elongation capacity for C18-C22 PUFA substrates in the S. olivacea Elovl4. The S. olivacea Elovl6 elongated saturated fatty acids, monounsaturated fatty acids, and interestingly, C18-C20 PUFA. Taken together, both Elovl fulfill the elongation steps required for conversion of C18 PUFA to their respective LC-PUFA products. Elovl4 is expressed mainly in the hepatopancreas and gill tissues, while Elovl6 is predominant in digestive tissues. The mRNA expression of both enzymes was higher in mud crabs fed with vegetable oil-based diets. Tissue fatty acid composition also showed the existence of LC-PUFA biosynthesis intermediate products in tissues expressing these two elongases. In summary, we report here two novel Elovl with PUFA elongating activities in a marine brachyuran. This will contribute significantly to the understanding of the LC-PUFA biosynthesis pathway in crustaceans and advance the development of aquafeed for intensive farming of the mud crab.

Role of Oxytocin/Vasopressin-Like Peptide and Its Receptor in Vitellogenesis of Mud Crab

Oxytocin (OT)/vasopressin (VP) signaling system is important to the regulation of metabolism, osmoregulation, social behaviours, learning, and memory, while the regulatory mechanism on ovarian development is still unclear in invertebrates. In this study, Spot/vp-like and its receptor (Spot/vpr-like) were identified in the mud crab Scylla paramamosain. Spot/vp-like transcripts were mainly expressed in the nervous tissues, midgut, gill, hepatopancreas, and ovary, while Spot/vpr-like were widespread in various tissues including the hepatopancreas, ovary, and hemocytes. In situ hybridisation revealed that Spot/vp-like mRNA was mainly detected in 6–9th clusters in the cerebral ganglion, and oocytes and follicular cells in the ovary, while Spot/vpr-like was found to localise in F-cells in the hepatopancreas and oocytes in the ovary. In vitro experiment showed that the mRNA expression level of Spvg in the hepatopancreas, Spvgr in the ovary, and 17β-estradiol (E₂) content in culture medium were significantly declined with the administration of synthetic SpOT/VP-like peptide. Besides, after the injection of SpOT/VP-like peptide, it led to the significantly reduced expression of Spvg in the hepatopancreas and subduced E₂ content in the haemolymph in the crabs. In brief, SpOT/VP signaling system might inhibit vitellogenesis through neuroendocrine and autocrine/paracrine modes, which may be realised by inhibiting the release of E₂.

DNA Methylation Inhibits the Expression of CFSH in Mud Crab

Crustacean female sex hormone (CFSH) is a key regulator of crustacean sex differentiation. The expression of Sp-CFSH in the mud crab Scylla paramamosain showed a tissue-specific and gender-variant pattern. To explore the role of DNA methylation in Sp-CFSH expression, the 5'-flanking region of Sp-CFSH was cloned, and one CpG island containing 12 CpG sites was found. Results of sodium bisulfite sequencing and methylated DNA immunoprecipitation showed that CpG island methylation was stable in the eyestalk ganglion during ovarian development of the females, which was significantly lower than that in the muscle of the females and in the eyestalk ganglion of the males. Such results suggested that the involvement of DNA methylation in regulating Sp-CFSH expression followed an eyestalk ganglion-specific and gender-variant pattern. The analysis of CpG dinucleotide site methylation and activity of the site-directed mutation (SDM) reporter vector further demonstrated that methylation inhibited Sp-CFSH expression by blocking the binding of transcription factor Sp1. The finding suggested for the first time the involvement of CpG methylation in the regulation of Sp-CFSH expression.

Serotonergic Mechanisms of Oocyte Germinal Vesicle Breakdown in the Mud Crab, Scylla paramamosain

The mechanism of serotonin (5-HT)-induced oocyte germinal vesicle breakdown (GVBD) in the mud crab, Scylla paramamosain, was investigated in this study. Histological staining showed that there were two meiotic arrests in oocyte, appearing at prophase I and metaphase I. This result indicated that meiosis I arrest at prophase I in S. paramamosain was similar to that of vertebrates, but meiosis II arrest at metaphase I was different from that of vertebrates. Resumption of oocytes arrest at meiosis prophase I could be induced by 5-HT rapidly within 5 min in S. paramamosain. We obtained the sequence of the 5-HT receptor type 1A (5-HTR_1A) from the NCBI database, and found that 5-HTR_1A was expressed in oocytes and follicle cells. In addition, we found that an agonist 8-OH-DPAT which binds 5-HTR_1A induced GVBD and an antagonist WAY100635 which inhibited 5-HT induced GVBD in S. paramamosain. This result showed that 5-HTR_1A mediated the regulation of oocyte GVBD by 5-HT. To explore the functional mechanism of 5-HT in inducing oocyte GVBD, forskolin, a cAMP agonist was used. Results showed that, forskolin significantly blocked 5-HT-induced GVBD, and there was a negative correlation between GVBD rate and cAMP level. Our data indicate that there are two meiotic arrests in S. paramamosain, and the resumption of prophase I arrest can be induced by 5-HT, which binds to 5-HTR_1A, and this process is mediated by cAMP, which acts as negative regulator via cAMP signaling pathway.

Crustacean Female Sex Hormone From the Mud Crab Scylla paramamosain Is Highly Expressed in Prepubertal Males and Inhibits the Development of Androgenic Gland

Recently, the crustacean female sex hormone (CFSH), which is considered a female-specific hormone, has been shown to play a crucial role in female phenotypes in crustaceans. In this study, two transcripts (Sp-CFSH1 and Sp-CFSH2) encoding the same CFSH precursor were cloned from the mud crab Scylla paramamosain. Homology and phylogenetic analysis showed that CFSHs were homologous to interleukin-17 and highly conserved among brachyuran crabs. PCR analysis revealed that Sp-CFSH was expressed exclusively in the eyestalk ganglion of both prepubertal males and females, and surprisingly, the abundance of Sp-CFSH transcripts detected in the males were not significantly different from that of the females (P > 0.05). In addition, mRNA in situ hybridization showed that Sp-CFSH was localized in the X-organ of the male eyestalk ganglion. During the development of the androgenic gland (AG), the level of Sp-IAG mRNA in AG remained at low levels from stages I to II (early stage) but had a significant increase at stage III (mature stage). In contrast, the level of Sp-CFSH transcripts in the eyestalk ganglion was high in the early stage but extremely low in the mature stage. To investigate the potential function of CFSH in male S. paramamosain, the recombinant protein (∼20 kDa) was expressed in Escherichia coli and was subsequently added to AG explants in vitro. It was demonstrated that recombinant Sp-CFSH protein significantly reduced the expression of Sp-IAG in the AG explants at a concentration of 10-6 M (P < 0.05). In conclusion, our study provides the first piece of evidence that shows CFSH from the eyestalk ganglion acts as a negative regulator inhibiting the development of AG in crustaceans.