Penaeus Japonicus Research Articles

Tropical seascapes as feeding grounds for juvenile penaeid shrimps in southern Mozambique revealed using stable isotopes

The feeding grounds for four of the most commercially important penaeid shrimp species (Metapenaeus monoceros, M. stebbingi, Penaeus japonicus and Penaeus indicus) within the mangrove and its adjacent coastal habitats (sand flat, mud flat and seagrass meadows) were investigated at Saco and Sangala bays (Inhaca Island, Mozambique, southern-East Africa). The study used carbon and nitrogen stable isotope ratios to identify the potential food sources for the different shrimp species within each habitat. Significant differences (p < 0.05) in terms of stable isotopes were observed among potential food sources in each habitat in both Saco and Sangala bays (isotopic ratios discriminating habitats), as well as between shrimp species among the different habitats. No ontogenetic dietary shifts were found for the studied penaeid shrimp species. The mangrove habitat did not provide a direct food source for most of the species at Saco and Sangala Bays. The seagrass habitat appeared to be a primary feeding area, mainly through seagrass, sediment, polychaetes and seston. The mud and sand flat habitats contributed with less food items for the shrimp species at Saco Bay, as well as the sand flat habitat at Sangala Bay. The possibility to identify feeding grounds is a fundamental tool to assist conservation of the resources and their habitat and for applying an ecosystem approach to fishery management.

Shrimp miR-12 Suppresses White Spot Syndrome Virus Infection by Synchronously Triggering Antiviral Phagocytosis and Apoptosis Pathways.

Growing evidence has indicated that the innate immune system can be regulated by microRNAs (miRNAs). However, the mechanism underlying miRNA-mediated simultaneous activation of multiple immune pathways remains unknown. To address this issue, the role of host miR-12 in shrimp (Marsupenaeus japonicus) antiviral immune responses was characterized in the present study. The results indicated that miR-12 participated in virus infection, host phagocytosis, and apoptosis in defense against white spot syndrome virus invasion. miR-12 could simultaneously trigger phagocytosis, apoptosis, and antiviral immunity through the synchronous downregulation of the expression of shrimp genes [PTEN (phosphatase and tensin homolog) and BI-1(transmembrane BAX inhibitor motif containing 6)] and the viral gene (wsv024). Further analysis showed that miR-12 could synchronously mediate the 5′–3′ exonucleolytic degradation of its target mRNAs, and this degradation terminated in the vicinity of the 3′ untranslated region sequence complementary to the seed sequence of miR-12. Therefore, the present study showed novel aspects of the miRNA-mediated simultaneous regulation of multiple immune pathways.

The Color of Marine Shrimps and Its Role in the Aquaculture

In the present review, we have described aspects of the color of marine shrimp of importance in aquaculture (mainly Penaeus japonicus, Litopenaeus vannamei and Penaeus monodon) and in the world. It is generally described some ecological aspects and some factors that affect the color of the shrimp.

Beneficial effects of dietary supplemented Parachlorella kessleri strain KNK-A001 on pacific white shrimp (Litopenaeus vannamei) and kuruma shrimp (Marsupenaeus japonicus)

Beneficial effects of dietary supplemented Parachlorella kessleri strain KNK-A001 on pacific white shrimp (Litopenaeus vannamei) and kuruma shrimp (Marsupenaeus japonicus)

EFFECTS OF DIETARY PYRIDOXINE LEVELS ON GROWTH AND VITAMIN B6 PROFILE OF JUVENILE KURUMA PRAWN, Penaeus japonicus

The effects of dietary pyridoxine levels (0, 5, 15. and 25mg/100g diet) on growth andvitamin 86 profile of' juvenile Penaeus japonicus (0.69 + 0.03g; mean + sd) wereinvestigated during 8 weeks of f'eeding experiments.

Scavenger receptor C promotes bacterial clearance in kuruma shrimp Marsupenaeus japonicus by enhancing hemocyte phagocytosis and AMP expression

Scavenger receptors (SRs) comprise a large family of structurally diverse glycoproteins located on the cell membrane and function as pattern-recognition receptors (PRRs) participating in innate immunity in different species. Class C scavenger receptor (SRC) has been only identified in invertebrates and its biological functions still need to be researched. In this study, we characterized the anti-bacterial function of a SRC from kuruma shrimp Marsupenaeus japonicus (MjSRC). The mRNA level of MjSRC was up-regulated significantly in hemocytes of kuruma shrimp challenged by Vibrio anguillarum or Staphylococcus aureus. The recombinant extracellular domains (MAM and CCP domains) of MjSRC have the ability of binding different bacteria and glycans in vitro. After knockdown of MjSRC, the bacterial clearance ability and phagocytic rate of hemocyte decreased significantly in vivo. Meanwhile, overexpression of MjSRC in shrimp enhanced the clearance ability and phagocytic rate of hemocytes. Further study found that MjSRC could regulate the expression of several antimicrobial peptides (AMPs). All these results indicate that MjSRC plays important roles in antibacterial immunity in kuruma shrimp by enhancing hemocyte phagocytosis and AMP expression.

The crustin-like peptide plays opposite role in shrimp immune response to Vibrio alginolyticus and white spot syndrome virus (WSSV) infection

Crustin is an antimicrobial peptide (AMP) that plays a key role in innate immunity of crustaceans. In this study, we cloned the entire 660 bp crustin-like sequence with a 507 bp open reading frame encoding a 168 amino acid from Marsupenaeus japonicus. The crustin-like gene was primarily expressed in gills and over-expressed in shrimp hemocytes after challenge with WSSV or Vibrio alginolyticus. After knockdown crustin-like gene using specific double-stranded RNA (CRU-dsRNA), IMD, Rab7, L-lectin, mitogen-activated protein kinase, p53, prophenoloxidase and Rho were down-regulated and nitric oxide synthase, myosin and tumor necrosis factor-α were up-regulated in hemocytes at 24 h post dsRNA treatment. After WSSV challenge, The mortality, WSSV copy number and expressions of WSSV immediate early genes (IE1, IE2, DNA polymerase, VP28) were both decreased but the apoptosis rate was increased in CRU-dsRNA-treated shrimps, indicating that WSSV may take advantage of crustin-like to benefit its replication. After silenced the crustin-like, the results of phagocytosis showed that the phagocytic rate of shrimp hemocytes on WSSV decreased significantly. In contrast, the absence of crustin-like in shrimps increased the mortality following V. alginolyticus challenge, indicating that crustin-like may play a positive role in the antibacterial process. The phagocytosis experiment showed there was a higher phagocytosis rate of hemocytes after CRU-dsRNA treatment. The result indicated that V. alginolyticus may be able to use crustin-like to avoid phagocytosis of shrimp hemocytes. These results further added to our understanding of the function of crustin-like peptide and also provided its potential role in innate immunity in shrimp.

Novel Pattern Recognition Receptor Protects Shrimp by Preventing Bacterial Colonization and Promoting Phagocytosis.

The recognition of pathogen-associated molecular patterns is accomplished by the recognition modules of pattern recognition receptors (PRRs). Leucine-rich repeats (LRRs) and C-type lectin-like domain (CTLD) represent the two most universal categories of recognition modules. In the current study, we identified a novel soluble and bacteria-inducible PRR comprising LRRs and a CTLD from the hepatopancreas of kuruma shrimp Marsupenaeus japonicus and named it Leulectin. The module arrangement of Leulectin is unique among all organisms. Both modules, together with the whole molecule, protected shrimp against Vibrio infection. By screening the pathogen-associated molecular patterns that shrimp might encounter, Leulectin was found to sense Vibrio flagellin through the LRRs and to recognize LPS through CTLD. The LRR-flagellin interaction was confirmed by pull-down and far-Western assays and was found to rely on the fourth LRR of Leulectin and the N terminus of flagellin. The recognition of LPS was determined by the long loop region of CTLD in a calcium-independent manner. By sensing the flagellin, LRRs could prevent its attachment to shrimp cells, thereby inhibiting Vibrio colonization. With the ability to recognize LPS, CTLD could agglutinate the bacteria and promote hemocytic phagocytosis. Our study clearly showed the division of labor and the synergy between different recognition modules and provided new insights into the concept of pattern recognition and the function of soluble PRRs in the antibacterial response.

Effect of the dietary probiotic Clostridium butyricum on growth, intestine antioxidant capacity and resistance to high temperature stress in kuruma shrimp Marsupenaeus japonicus

A 56-day feeding trial followed by an acute high temperature stress test were performed to evaluate the effect of dietary probiotic Clostridium butyricum (CB) on growth performance and intestine antioxidant capacity of kuruma shrimp Marsupenaeus japonicus. Shrimp were randomly allocated in 9 tanks (30 shrimp per tank) and triplicate tanks were fed with diets containing different levels of C. butyricum (1×109 cfu/g): 0mgg−1 feed (Control), 100mgg−1 feed (CB-100), 200mgg−1 feed (CB-200) as treatment groups. The results indicated that dietary supplementation of C. butyricum increased the growth performance and decreased the feed conversion rate (FCR) of shrimp in the CB-100 group. HE stain showed that C. butyricum increased the intestine epithelium height of M. japonicus. C. butyricum supplemented in diets decreased·O2- generation capacity and malondialdehyde (MDA) content, and increased total antioxidant capacity (T-AOC), catalase (CAT) and peroxidase (POD) activity and the expression level of heat shock protein 70 (hsp70) and metallothionein (mt) gene in intestine of shrimp cultured under normal condition for 56 d, while no significant changes in glutathione peroxidase (GPx) activity and ferritin gene expression level. After shrimp exposed to high temperature stress 48h, the lower level of·O2- generation capacity and MDA content, and the higher level survival, activities of T-AOC, CAT, GPx and POD, as well as hsp70, ferritin and mt gene expression level were found in intestine of two C. butyricum groups. These results revealed that C. butyricum could improve the growth performance, increase intestine antioxidant capacity of M. japonicus against high temperature stress, and could be a potential feed additive in shrimp aquaculture.

Pathogen recognition of a novel C-type lectin from Marsupenaeus japonicus reveals the divergent sugar-binding specificity of QAP motif

C-type lectins (CTLs) are calcium-dependent carbohydrate-binding proteins known to assist the innate immune system as pattern recognition receptors (PRRs). The binding specificity of CTLs lies in the motif of their carbohydrate recognition domain (CRD), the tripeptide motifs EPN and QPD bind to mannose and galactose, respectively. However, variants of these motifs were discovered including a QAP sequence reported in shrimp believed to have the same carbohydrate specificity as QPD. Here, we characterized a novel C-type lectin (MjGCTL) possessing a CRD with a QAP motif. The recombinant MjGCTL has a calcium-dependent agglutinating capability against both Gram-negative and Gram-positive bacteria, and its sugar specificity did not involve either mannose or galactose. In an encapsulation assay, agarose beads coated with rMjGCTL were immediately encapsulated from 0 h followed by melanization at 4 h post-incubation with hemocytes. These results confirm that MjGCTL functions as a classical CTL. The structure of QAP motif and carbohydrate-specificity of rMjGCTL was found to be different to both EPN and QPD, suggesting that QAP is a new motif. Furthermore, MjGCTL acts as a PRR binding to hemocytes to activate their adherent state and initiate encapsulation.

Two White Spot Syndrome Virus MicroRNAs Target the Dorsal Gene To Promote Virus Infection in Marsupenaeus japonicus Shrimp.

In eukaryotes, microRNAs (miRNAs) serve as regulators of many biological processes, including virus infection. An miRNA can generally target diverse genes during virus-host interactions. However, the regulation of gene expression by multiple miRNAs has not yet been extensively explored during virus infection. This study found that the Spaztle (Spz)-Toll-Dorsal-antilipopolysaccharide factor (ALF) signaling pathway plays a very important role in antiviral immunity against invasion of white spot syndrome virus (WSSV) in shrimp (Marsupenaeus japonicus). Dorsal, the central gene in the Toll pathway, was targeted by two viral miRNAs (WSSV-miR-N13 and WSSV-miR-N23) during WSSV infection. The regulation of Dorsal expression by viral miRNAs suppressed the Spz-Toll-Dorsal-ALF signaling pathway in shrimp in vivo, leading to virus infection. Our study contributes novel insights into the viral miRNA-mediated Toll signaling pathway during the virus-host interaction.IMPORTANCE An miRNA can target diverse genes during virus-host interactions. However, the regulation of gene expression by multiple miRNAs during virus infection has not yet been extensively explored. The results of this study indicated that the shrimp Dorsal gene, the central gene in the Toll pathway, was targeted by two viral miRNAs during infection with white spot syndrome virus. Regulation of Dorsal expression by viral miRNAs suppressed the Spz-Toll-Dorsal-ALF signaling pathway in shrimp in vivo, leading to virus infection. Our study provides new insight into the viral miRNA-mediated Toll signaling pathway in virus-host interactions.

Prevalence and distribution of covert mortality nodavirus (CMNV) in cultured crustacean

An emerging covert mortality nodavirus (CMNV) was proved to be the infectious agent of shrimp viral covert mortality disease (VCMD). Prevalence and distribution of CMNV were investigated by using the methods of reverse transcription loop-mediated isothermal amplification (RT-LAMP), nested reverse transcription PCR, gene sequencing, histopathology, in situ RNA hybridization (ISH) and transmission electron microscope (TEM) in this study. RT-LAMP results showed that CMNV positive samples appeared in the cultured crustaceans including Litopenaeus vannamei, Fenneropenaeus chinensis, Marsupenaeus japonicus, Penaeus monodon, and Macrobrachium rosenbergii, and mostly distributed the coastal provinces in China. The prevalence rates of CMNV among the collected samples in 2013, 2014 and 2015 were 45.93% (130/283), 27.91% (84/301) and 20.85% (54/259), respectively. CMNV infection in M. japonicas and P. monodon was verified by ISH. The presence of CMNV particles were confirmed by TEM analysis in the CMNV positive samples diagnosed by RT-LAMP. The high prevalence and wide epidemic distribution of CMNV in this investigation revealed that it was necessary to pay close attention to the high risk of CMNV transmission in farmed crustaceans.

Effects of maternal influences and timing of spawning on intraspecific variations in larval qualities of the Kuruma prawn Marsupenaeus japonicus

Decreases in intraspecific variations in offspring qualities resulting from reductions in female body size in harvested populations can reduce the ability of these species to adapt to variations in environmental conditions. This, in turn, may result in greater fluctuations in recruitment of resources. In species in which offspring quality differs by female parent size, preserving differences and preventing limitations in female size among populations would be important. The effects of maternal factors on intraspecific variations in larval quality of the Kuruma prawn (Marsupenaeus japonicus) were analyzed by determining the relationships between larval variability (body size and resistance to starvation) and maternal variability (maternal body size, spawning timing, and maternal body condition) in the laboratory from June to October 2015. In addition, temporal variations in parental body size of fished M. japonicus stock were examined by field investigation for ten years between 1996 and 2010 in Bungo-suido Channel, Japan. Body size and starvation resistance of hatched larvae varied by spawning timing (spawning date) and corresponded with seasonal availability of food for larvae in the field. Larger females produced larger larvae with stronger starvation resistance. The mean size of harvested female prawns has decreased significantly over time. Stocks of M. japonicus with reduced mean female size would show reductions in intraspecific variations in quality and quantity of larvae at the population level, resulting from observed maternal influences and size-dependent female reproductive potential. If fishing activity reduces body size, marine reserves can be used as a possible management option.

Death associated protein 1 (DAP 1) positively regulates virus replication and apoptosis of hemocytes in shrimp Marsupenaeus japonicus

Death-associated protein 1 (DAP1) is a small proline-rich cytoplasmic protein that functions both in the apoptosis and autophage process of mammalian and in the clinical cancer of human. However, little knowledge is known about the homologue gene of DAP1 and its roles in the physiological process of invertebrates. In this paper, we report a novel function of DAP1 in the antivirus immunity of shrimp. A homologue gene of DAP1 was cloned from Marsupenaeus japonicus and named as Mjdap-1. The full-length of Mjdap-1 was 1761 bp with a 309 bp open reading frame that encoded 102 amino acids. Reverse transcription-PCR results showed that Mjdap-1 was expressed in all tested tissues, including hemocytes, gills, intestines, stomach, heart, hepatopancreas, testes, and ovaries. In shrimp, Mjdap-1 transcripts were up-regulated by white spot syndrome virus (WSSV) infection; Mjdap-1 knockdown decreased the virus copy in vivo and the mortality of M. japonicus to WSSV challenge. Conversely, injecting the purified recombinant MjDAP1 protein promoted the amplification of virus in shrimp. Flow cytometric assay showed, the virus infection-induced apoptosis of hemocytes was enhanced by MjDAP1 protein injection and inhibited in MjDAP1 knockdown shrimp. Furthermore, the expression of apoptosis-inducing factor (AIF) was regulated by Mjdap-1, but the caspase transcripts were not affected. Our results suggested that MjDAP1 facilitated the amplification of virus in shrimp, which may be attributed to the promotion of hemocyte apoptosis in an AIF-dependent manner. These results provided a new insight into the function of this protein that may be used for virus disease control.

Interaction of the Small GTPase Cdc42 with Arginine Kinase Restricts White Spot Syndrome Virus in Shrimp.

Many types of small GTPases are widely expressed in eukaryotes and have different functions. As a crucial member of the Rho GTPase family, Cdc42 serves a number of functions, such as regulating cell growth, migration, and cell movement. Several RNA viruses employ Cdc42-hijacking tactics in their target cell entry processes. However, the function of Cdc42 in shrimp antiviral immunity is not clear. In this study, we identified a Cdc42 protein in the kuruma shrimp (Marsupenaeus japonicus) and named it MjCdc42. MjCdc42 was upregulated in shrimp challenged by white spot syndrome virus (WSSV). The knockdown of MjCdc42 and injection of Cdc42 inhibitors increased the proliferation of WSSV. Further experiments determined that MjCdc42 interacted with an arginine kinase (MjAK). By analyzing the binding activity and enzyme activity of MjAK and its mutant, ΔMjAK, we found that MjAK could enhance the replication of WSSV in shrimp. MjAK interacted with the envelope protein VP26 of WSSV. An inhibitor of AK activity, quercetin, could impair the function of MjAK in WSSV replication. Further study demonstrated that the binding of MjCdc42 and MjAK depends on Cys271 of MjAK and suppresses the WSSV replication-promoting effect of MjAK. By interacting with the active site of MjAK and suppressing its enzyme activity, MjCdc42 inhibits WSSV replication in shrimp. Our results demonstrate a new function of Cdc42 in the cellular defense against viral infection in addition to the regulation of actin and phagocytosis, which has been reported in previous studies. IMPORTANCE The interaction of Cdc42 with arginine kinase plays a crucial role in the host defense against WSSV infection. This study identifies a new mechanism of Cdc42 in innate immunity and enriches the knowledge of the antiviral innate immunity of invertebrates.

Adenosine monophosphate degradation and inosinic acid accumulation in the shrimp Penaeus japonicus

Shrimp muscle contains taste component compounds, such as glutamic acid and inosinic acid (IMP). When both are present, taste intensity increases by fourfold to eightfold compared to that when only glutamic acid is present. Inosinic acid is generated via adenosine triphosphate degradation in two metabolic pathways in which adenosine monophosphate (AMP) is generated and then degraded to either IMP or adenosine (AdR). We investigated post-mortem AMP degradation pathways in the shrimp Penaeus japonicus by measuring the activity of enzymes extracted from shrimp muscle and by isolating bacteria from shrimp muscle and examining their role in AMP degradation. The enzyme extract degraded AMP to IMP through high AMP deaminase activity, and in addition, we identified Shewanella sp. and Exiguobacterium sp. as mediating AMP degradation to AdR. Therefore, preventing an increase in bacterial numbers during storage is important for preventing AMP from degrading to AdR.

Identification and molecular characterization of Cathepsin L gene and its expression analysis during early ontogenetic development of kuruma shrimp Marsupenaeus japonicus

Cathepsin L gene is a member of the cysteine proteinase gene group. In this study Cathepsin L gene was isolated from Kuruma shrimp Marsupenaeus japonicus (Mj-Cathepsin L) and the full-length DNA sequence was 1 963 bp. Mj-Cathepsin L protein showed high homologies with other Cathepsin L proteins documented in vertebrates, mollusks and other crustaceans. Expression analysis of Mj-Cathepsin L gene in different tissues revealed that it was predominant in hepatopancreas. During early ontogenetic development stages Mj-Cathepsin L showed a development-regulated expression, and the Mj-Cathepsin L showed a molting stage-regulated expression during the five molting stages, inferring its role in the ontogenic development of M. japonicus. Two kinds of forms of Mj-Cathepsin L protein: pro-Cathepsin L and Cathepsin L were measured in hepatopancreas, stomach and intestine by Western Blotting.

Purification and characterization of bioactive peptides RYamide and CCHamide in the kuruma shrimp Marsupenaeus japonicus

To understand the regulation systems of appetite, bioactive peptides from the kuruma shrimp Marsupenaeus japonicus (Mj) were isolated and purified by reverse pharmacological assays using CHO cells expressing the Drosophila melanogaster G-protein-coupled receptors (GPCRs) CG5811 (a RYamide receptor) or CG14593 (a CCHamide-2 receptor). Four peptides having binding activity to GPCRs were obtained and named Mj RYamide-1, Mj RYamide-2, Mj RYamide-3, and Mj CCHamide. Genes encoding the prepropeptides of these peptides were identified using kuruma shrimp transcriptome databases. The Mj prepro-RYamide gene encodes a 130-amino acid polypeptide containing Mj RYamide-1, Mj RYamide-2, and Mj RYamide-3, whereas the Mj prepro-CCHamide gene encodes a 119-amino acid polypeptide containing a single Mj CCHamide peptide. The expression of these genes was confirmed in various neuronal organs including the brain and ventral nerve cord. In addition, prepro-RYamide gene expression is significantly reduced in the brain after starvation. RYamides may thus be associated with regulation of feeding or digestion. Changes in kayak (the c-fos ortholog in invertebrates) gene expression after administration of synthetic peptides were also investigated. Mj kayak expression levels are upregulated in hepatopancreas after treatment with Mj RYamide-3 or CCHamide. Thus, the peptides isolated in this study may have some regulatory effect on cellular metabolism in aquacultured invertebrates.

In silico identification and characterization of putative kuruma prawn (Marsupenaeus japonicus) allergens

Background: Prawn is one of the major sources of shellfish allergens, which will induce mild to severe allergic reactions. Aim: The objective of this study was to predict putative allergens and its characteristics present in Marsupenaeus japonicus through an in silico approach. Materials And Methods: In this present study, in silico tools, RaptorX, Bepipred Linear Epitope and Parker Hydrophilicity Prediction method, and MHC2Pred were used to predict the putative and cross-reactive allergens, tertiary and secondary structures, B-cell linear epitopes, and T-cell epitopes, respectively. Results: As a result, eight putative and cross-reactive allergens including tropomyosin fast isoform, arginine kinase, sarcoplasmic calcium binding protein, myosin light chain, chymotrypsin like proteinase, superoxide dismutase, cathepsin B, and trypsin were predicted by analyzing the protein sequences of M. japonicus. Furthermore, five amino acids (Ala, Ser, Asn, Gly, and Lys) play a vital role in immunoglobulin E binding allergenic epitope. At least one of them was found in the predicted B-cell epitope for each of the predicted putative allergens. Moreover, the predicted T-cell epitopes were highly associated with human leukocyte antigen (HLA) DRB1*0101 and HLA-DRB1*0901 alleles while mediating T-cell immune responses. Conclusion: These results can be utilized to contribute in peptide immunotherapy and reduce the allergic diseases related to shellfish.

Mercury and selenium levels, and their molar ratios in several species of commercial shrimp in Japan regarding the health risk of methylmercury exposure.

The Japanese shrimp industry depends on importing shrimp from other countries. However, little information is available on mercury speciation and selenium (Se) concentrations in commercial shrimp available in Japan. The present study determined the concentrations of total mercury (T-Hg), methylmercury (MeHg), and Se in the muscles (wet weight) of imported and domestic commercial shrimp from Kumamoto and Kagoshima prefectures to obtain information for assessing the risk of MeHg exposure. The median concentrations of T-Hg, MeHg and Se in shrimp imported from three different countries were, respectively: black tiger shrimp (n = 18), 15.8, 14.4, and 415 ng/g; Vannamei shrimp (n = 25), 11.4, 11.2, and 292 ng/g; and white shrimp (n = 26), 26.8, 26.1, and 396 ng/g. There were significant differences in T-Hg and MeHg concentrations between shrimp imported from different countries. The median concentrations of T-Hg, MeHg and Se in shrimp of Japanese origin were, respectively: Shiba shrimp (n = 10), 15.9, 15.0, and 270 ng/g; Kuruma shrimp (n = 10), 79.9, 75.9, and 390 ng/g; and Ashiaka shrimp (n = 10), 36.1, 34.1, and 303 ng/g. The percentages of MeHg in T-Hg were between 90% and 99%, with MeHg levels in the imported and domestic commercial shrimp lower than the Japanese regulation of 300 ng/g for fish. The mean Se/T-Hg molar ratios (16-160) were comparatively higher than those previously reported in fish. Overall, this survey suggests that shrimp commercially available in Japan will not pose a particularly high risk regarding MeHg exposure to consumers.