A Comprehensive Review on Crustaceans' Immune System With a Focus on Freshwater Crayfish in Relation to Crayfish Plague Disease

Phosphorylated Eriocheir sinensis Rab10 regulates apoptosis and phagocytosis to defense Spiroplasma eriocheiris infection

The Rab GTPases play a crucial role in the regulation of immune responses towards viruses and bacteria infection in invertebrates. The proteomic data revealed Eriocheir sinensis Rab10 (EsRab10) phosphorylation was strongly decreased following Spiroplasma eriocheiris infection. However, the regulatory mechanism by which Rab10 modulates the innate immunity of E. sinensis against S. eriocheiris infection remains to be elucidated. In the present study, the coding sequence of EsRab10 identified as 609 bp, encoding a protein of 203 amino acids. EsRab10 was highly transcribed in diverse immune-related tissues of crab, including hepatopancreas, gills, and hemocytes, with a notable downregulation observed after S. eriocheiris infection. Knockdown of EsRab10 via RNA interference (RNAi) led to a significant increase in hemocyte apoptosis and a marked reduction in the phagocytic capacity of hemocytes against S. eriocheiris. Furthermore, EsRab10 RNAi resulted in an elevated S. eriocheiris load in hemocytes and a significant decrease in crab survival rates. Overexpression of EsRab10 in Drosophila Schneider 2 (S2) cells demonstrated that phosphorylation of EsRab10 enhanced cell viability, reduced apoptosis, increased phagocytic activity, and decreased the S. eriocheiris load in S2 cells. Conversely, dephosphorylation of EsRab10 exerted opposite effects. In summary, these results demonstrated that EsRab10 played a crucial role in the resistance of E. sinensis to S. eriocheiris infection by modulating apoptosis and phagocytosis through phosphorylation.

Effects of Different Sediment Improvers on the Growth Environment, Innate Immune Responses, and Intestinal Health of Procambarus clarkii

Sediment improvers are important mediators of aquatic animals' growth performance and the surrounding environmental quality. However, the physiological responses of crayfish (Procambarus clarkii) to different sediment improvers remain unclear. Here, we cultivated crayfish using two chemical (potassium monopersulfate and potassium ferrate) and two biological (purple nonsulfur photosynthetic bacteria and Bacillus subtilis) sediment improvers at low and high concentrations. After 42 days, we found that the addition of chemical sediment improvers was more effective in improving water quality than biological sediment improvers (e.g., more stable pH and lower nutrient concentrations). By contrast, the application of biological sediment improvers resulted in considerably enhanced final weight, weight gains, and survival rates. In all low-concentration groups, the activity of immune-related enzymes (e.g., superoxide dismutase and glutathione peroxidase) in the hemolymph and hepatopancreas considerably increased, whereas the malondialdehyde activity and mRNA expression of AMP genes (PcALF and PcCru) considerably decreased. Crayfish exposed to low concentrations of sediment improvers exhibited enhanced intestinal and hepatopancreatic integrity, with a thickened mucosal layer and increased density of epithelial cell granules. Additionally, the composition of the gut microbiota varied after the addition of different sediment improvers. In summary, our research indicated that different types of sediment improvers not only improved the farming environment but also had varying effects on crayfish. Therefore, an appropriate sediment improver based on specific aquaculture conditions is needed.

Expression of C/EBP and Kr-h1 transcription factors under immune stimulation in the noble crayfish

Transcription factors (TFs) have an important role in the regulation of the gene expression network. The role of TFs in the immune response of freshwater crayfish is poorly understood, but leveraging the regulatory mechanisms of immune response could augment the resistance against the invasive oomycete pathogen, Aphanomyces astaci. Previous studies indicated that the TFs CCAAT/enhancer-binding protein (C/EBP) and putative Krüppel homolog-1 protein (Kr-h1) might play a role in immune and stress response of the noble crayfish (Astacus astacus). Here, we aimed to further characterise these two gene products to gain a better understanding of their evolutionary origin, domain organisation and expression patterns across different crayfish tissues. Furthermore, we conducted an immune stimulation experiment to observe the potential changes in the gene expression of C/EBP and Kr-h1 under immune challenge in different crayfish tissues. Our results showed that both C/EBP and Kr-h1 are closely related to other C/EBPs and Kr-h1s in Malacostraca. Gene expression analysis revealed that both TFs are present in all analysed tissues, with higher expression of C/EBP in the gills and Kr-h1 in the abdominal muscle. Immune stimulation with laminarin (mimicking β-1-3-glucan in the oomycete cell wall) showed an activation of the crayfish immune system, with an overall increase in the total haemocyte count (THC) compared to untreated control and crayfish buffered saline (CBS) treatment. On the gene expression level, an up-regulation of the C/EBP gene was detected in the laminarin treated group in hepatopancreas and heart, while no changes were observed for the Kr-h1 gene. Our results indicate an early change in C/EBP expression in multiple tissues during immune stimulation and suggest its involvement in the immune response of the noble crayfish.

Comprehensive analysis of the mRNA and miRNA transcriptome implicated in the immune response of Procambarus clarkii to Spiroplasma eriocheiris

In recent years, the red swamp crayfish (Procambarus clarkii, P. clarkii) farming industry has suffered huge economic losses due to the pathogenic bacterium Spiroplasma eriocheiris (S. eriocheiris). To elucidate the immune response mechanism and identify hub immune genes as well as their associated microRNAs that regulate the host response of P. clarkii against S. eriocheiris infection, we conducted a comprehensive analysis on P. clarkii hemocyte mRNA and microRNA (miRNA) transcriptomes at different infection stages using third- and second-generation sequencing technologies. In full-length transcriptome functional annotation, 8155 unigenes were annotated, and 1168 potential new transcripts were predicted. In the mRNA transcriptome, a total of 3168 differentially expressed genes were identified at different infection stages, including 1492 upregulated and 1676 downregulated genes (duplicate genes excluded). Transcriptome analysis revealed 880 differentially expressed genes involved in multiple pathways and processes such as endocytosis, autophagy, lysosome, mTOR signaling, phagosome, and the Fanconi anemia pathway. Mfuzz analysis was employed to integrate and cluster the differential expression trends of genes across the three infection stages. In the miRNA transcriptome, 234 miRNAs and 966 predicted target genes were identified, with 86 differentially expressed miRNAs identified across the three time periods. A significant difference (P < 0.05) was observed for miRNAs including pcl-miR-146-3p, pcl-miR-74-3p, pcl-miR-225-5p, and pcl-miR-68-5p. These miRNAs are involved in multiple immune and autophagy-related pathways and have regulatory effects on immune genes including Vps26, lqf, and ERK-A. Based on the differentially expressed immune-related genes, we constructed a protein-protein interaction (PPI) network, which revealed the interactions among hub genes including Rac1, Akt1, Rho1, and Egfr. We also constructed a miRNA-gene interaction network in immune and autophagy-related processes, highlighting the potential regulatory effects of miRNAs including pcl-miR-183-5p, pcl-miR-146-3p, pcl-miR-176-5p, and pcl-miR-225-5p on proteins including LST8, SNAP29, Rab-7A, and ERK-A. To conclude, this study has identified hub immune genes and corresponding regulatory miRNAs in P. clarkii hemocytes in response to S. eriocheiris infection and explored the roles of these genes in selected pathways and processes. These findings are expected to provide further insights into the molecular mechanisms that confer resistance to S. eriocheiris infection in P. clarkii.

Myeloid differentiation protein 2 regulates the innate immunity and the disease resistant against Vibrio alginolyticus in Scylla paramamosain

Myeloid differentiation protein 2 (MD2), generally functions as a coreceptor of Toll-like receptor 4 (TLR4), facilitating the activation of TLR4 and the recognition of lipopolysaccharides (LPS) in host organisms. While the role of MD2 in immune activation is well-documented across various species, the specific role of the MD2 homolog in Scylla paramamosain (SpMD2) remains unidentified. In this study, we applied RNA interference to reduce SpMD2 expression, aiming to elucidate its role in immune system of mud crabs. Notably, SpMD2 interference leded to decrease in the hemocyte counts and phagocytic activity, along with increase in apoptosis rates and level of reactive oxygen species (ROS). Furthermore, the activities of key enzymes related to immune, such as superoxide dismutase (SOD), catalase (CAT), phenoloxidase (PO), peroxidase (POD), lysozyme (LZM), and acid phosphatase (ACP), were reduced by SpMD2 knockdown. Following infection with Vibrio alginolyticus, increase of SpMD2 expression level was observed. This was accompanied by alterations in the expression levels of genes related to immune in mud crabs. Challenge experiment with Vibrio alginolyticus showed a higher mortality rate after SpMD2 interference. Our study underscore the critical role of SpMD2 in enhancing the innate immunity and disease resistant in S. paramamosain, advancing our understanding of the innate immune regulatory mechanisms in crustaceans.

The role of phagocytic cells in aging: insights from vertebrate and invertebrate models

While the main role of phagocytic scavenger cells consists of the neutralization and elimination of pathogens, they also keep the body fluids clean by taking up and breaking down waste material. Since a build-up of waste is thought to contribute to the aging process, these cells become particularly pertinent in the research field of aging. Nevertheless, a direct link between their scavenging functions and the aging process has yet to be established. Integrative approaches involving various model organisms hold promise to elucidate this potential, but are lagging behind since the diversity and evolutionary relationship of these cells across animal species remain unclear. In this perspective, we review the current knowledge associating phagocytic scavenger cells with aging in vertebrate and invertebrate animals, as well as put forward important questions for further exploration. Additionally, we highlight future challenges and propose a constructive approach for tackling them.

Zinc oxide-Ulva lactuca nanocomposite is a robust dietary immunostimulant in the red swamp crayfish (Procambarus clarkii)

Aquaculture industry suffers significant limitations such as low resistance to diseases and expensive feed. This study investigated the antibacterial and immunostimulatory activities of ZnO-Ulva lactuca nanocomposite (ZnO-Ul NC) in the Procambarus clarkii. Zinc oxide nanoparticles (ZnO NPs) and ZnO-Ul NC were synthetized and characterized by electron microscopies as well as Fourier transform infrared spectroscopy. ZnO NPs and ZnO-Ul NC inhibited the growth of the isolated species Citrobacter freundii and Enterobacter hormaechei. For immunostimulatory evaluation, six crayfish groups (control, U. lactuca, ZnO L, ZnO H, ZnO-Ul L, and ZnO-Ul H) were fed on commercial diet, Ulva lactuca powder, and low or high dose of ZnO NPs or ZnO-Ul NCs, respectively for 90 days. The highest levels of total hemocyte count, granular cells%, phenoloxidase (PO) activity in hemolymph, and NO, superoxide dismutase (SOD), and GSH in hepatopancreas were all reported in the ZnO-Ul groups. The expression of proPO, SOD, and lysozyme exhibited the highest upregulation in the ZnO-Ul H group. Taken together, dietary ZnO-Ul NC significantly improved the non-specific immunity and antioxidant milieu of the crayfish at the genomic and proteomic levels. ZnO-Ul NC is cost effective, easily synthesized, and a promising immunostimulant for Procambarus clarkii that could be used in the aquaculture.

Multiple Biomarker Responses in Aegla castro Exposed to Copper: A Laboratory Approach

Although some biomarkers have already been determined in aeglids collected in the field, data from laboratory exposures are scarce. To our knowledge, no studies have investigated oxidative stress biomarkers in aeglids exposed to metals in the laboratory, or performed hemocyte counts and the comet assay using gill and hepatopancreas of aeglids. Thus, we investigated the effects of acute Cu exposure on intermolt males of Aegla castro, collected from a reference stream, acclimated for 6 days in the laboratory, and then exposed to 11 μg L-1 of dissolved Cu (Cu 11) or only to water (CTR), for 24 h. Gill and hepatopancreas samples were used to determine Cu accumulation, DNA damage, and metallothionein content (MT), while hemolymph samples were used to determine Cu accumulation, DNA damage, and hemocyte counts. Muscle samples were used to determine Cu accumulation and acetylcholinesterase activity (AChE). Non-protein thiol content (NPSH), catalase (CAT), glutathione S-transferase activities (GST), lipoperoxidation (LPO), and protein carbonylation content (PCC) were measured only in the hepatopancreas. Aegla castro exposed to Cu accumulated this metal in gills and activated detoxification mechanisms, through increased MT content in the gill, and showed an immune response, evidenced by an increase in hyaline hemocytes. Therefore, gill and hemocytes appear to have a protective role in preventing the transport and bioavailability of Cu through the body. On the other hand, we observed a decrease in MT content in the hepatopancreas of crabs exposed to Cu, suggesting the excretion of MT in association with Cu bound to the sulfhydryl groups of this protein.

Dietary β-1,3-Glucan Promotes Growth Performance and Enhances Non-Specific Immunity by Modulating Pattern Recognition Receptors in Juvenile Oriental River Prawn (Macrobrachium nipponense)

As a typical pathogen-associated molecular pattern (PAMP), β-1,3-glucan can engage with pattern recognition receptors (PRRs) to initiate an immune response. In this study, we investigated the effects of dietary β-1,3-glucan on growth performance, antioxidant capacity, immune response, intestinal health, and bacterial resistance in juvenile Macrobrachium nipponense. Prawns were fed with five experimental diets containing 0%, 0.05%, 0.1%, 0.2%, and 0.4% β-1,3-glucan for eight weeks. The findings demonstrated that the inclusion of β-1,3-glucan improved weight gain and survival rate in prawns. Prawns fed with β-1,3-glucan exhibited elevated activities of hepatopancreatic ACP (acid phosphatase), AKP (alkaline phosphatase), and SOD (superoxide dismutase), while MDA (malondialdehyde) content was reduced. Expression levels of PRRs related genes including LGBP (lipopolysaccharide and β-1,3-glucan binding protein), lectin, and LBP (lipopolysaccharide-binding protein) were significantly increased in prawns fed with β-1,3-glucan. Intestinal flora analysis revealed suppression of Cyanobacteria abundance at the Phylum level and enhancement in Rhodobacter abundance at the genus level in prawns fed with a 0.2% β-1,3-glucan diet. Furthermore, prawns fed with 0.1%, 0.2%, and 0.4% β-1,3-glucan demonstrated significantly higher survival rates following Aeromonas hydrophila infection. In conclusion, β-1,3-glucan can activate PRRs to improve immune responses in M. nipponese. Within the range of β-1,3-glucan concentrations set in this experiment, it is recommended to add 0.18% of β-1,3-glucan to the diet, taking into account the positive effect of β-1,3-glucan on the survival rate of M. nipponensecu.

Effects of high temperature and LPS injections on the hemocytes of the crab Neohelice granulata

Temperature fluctuations, particularly elevated temperatures, can significantly affect immune responses. These fluctuations can influence the immune system and alter its response to infection signals, such as lipopolysaccharide (LPS). Therefore, this study was designed to investigate how high temperatures and LPS injections collectively influence the immune system of the crab Neohelice granulata. Two groups were exposed to 20 °C (control) or 33 °C for four days. Subsequently, half were injected with 10 μL of physiological crustacean (PS), while the rest received 10 μL of LPS [0.1 mg.kg-1]. After 30 min, the hemolymph samples were collected. Hemocytes were then isolated and assessed for various parameters using flow cytometry, including cell integrity, DNA fragmentation, total hemocyte count (THC), differential hemocyte count (DHC), reactive oxygen species (ROS) level, lipid peroxidation (LPO), and phagocytosis. Results showed lower cell viability at 20 °C, with more DNA damage in the same LPS-injected animals. There was no significant difference in THC, but DHC indicated a decrease in hyaline cells (HC) at 20 °C following LPS administration. In granular cells (GC), an increase was observed after both PS and LPS were injected at the same temperature. In semi-granular cells (SGC), there was a decrease at 20 °C with the injection of LPS, while at a temperature of 33 °C, the SGC there was a decrease only in SGC injected with LPS. Crabs injected with PS and LPS at 20 °C exhibited higher levels of ROS in GC and SGC, while at 33 °C, the increase was observed only in GC and SGC cells injected with LPS. A significant increase in LPO was observed only in SGC cells injected with PS and LPS at 20 °C and 33 °C. Phagocytosis decreased in animals at 20 °C with both injections and exposed to 33 °C only in those injected with LPS. These results suggest that elevated temperatures induce changes in immune system parameters and attenuate the immune responses triggered by LPS.

Transforming Aquaculture through Vaccination: A Review on Recent Developments and Milestones

Aquaculture has rapidly emerged as one of the fastest growing industries, expanding both on global and on national fronts. With the ever-increasing demand for proteins with a high biological value, the aquaculture industry has established itself as one of the most efficient forms of animal production, proving to be a vital component of global food production by supplying nearly half of aquatic food products intended for human consumption. As in classic animal production, the prevention of diseases constitutes an enduring challenge associated with severe economic and environmental repercussions. Nevertheless, remarkable strides in the development of aquaculture vaccines have been recently witnessed, offering sustainable solutions to persistent health-related issues challenging resilient aquaculture production. These advancements are characterized by breakthroughs in increased species-specific precision, improved vaccine-delivery systems, and innovations in vaccine development, following the recent advent of nanotechnology, biotechnology, and artificial intelligence in the -omics era. The objective of this paper was to assess recent developments and milestones revolving around aquaculture vaccinology and provide an updated overview of strengths, weaknesses, opportunities, and threats of the sector, by incorporating and comparatively discussing various diffuse advances that span across a wide range of topics, including emerging vaccine technologies, innovative delivery methods, insights on novel adjuvants, and parasite vaccine development for the aquaculture sector.

A pattern recognition receptor interleukin-1 receptor is involved in reproductive immunity in Macrobrachium nipponense ovary

The family of TIR domain-containing receptors includes numerous proteins involved in innate immunity. In this study, a member of this family was characterized from the ovary of the oriental river prawn Macrobrachium nipponense and identified as interleukin-1 receptor (MnIL-1R). Meanwhile, to elucidate the conservation of IL-1R, its orthologous were identified in several crustacean species as well. In addition, the expression pattern of MnIL-1R in various adult tissues and post different pathogen-associated molecular patterns (PAMPs) challenge in ovary was analyzed with qRT-PCR technology. Finally, the roles of MnIL-1R in the ovary were analyzed by RNAi technology. The main results are as follows: (1) MnIL-1R comprises a 1785 bp ORF encoding 594 amino acids and is structurally composed of five domains: a signal peptide, two immunoglobulin (IG) domains, a transmembrane region, and a TIR-2 domain; (2) the TIR domain showed a high conservation among analyzed crustacean species; (3) MnIL-1R is widely detected in all tested tissues including ovary; (4) MnIL-1R showed a positive response to challenges with LPS, PGN, and polyI:C in the ovary; (5) its IG domain showed strong binding ability to LPS and PGN, confirming its role as a pattern recognition receptor; (6) the expression patterns of several members of the Toll signaling pathway (Myd88, TRAF-6, Dorsal, and Relish) was similar to that of MnIL-1R after challenges with LPS, PGN, and polyI:C in the ovary; (7) the silencing of MnIL-1R resulted in down-regulation of theses gene' (Myd88, TRAF-6, Dorsal, and Relish) expression level in the ovary. These results suggest that MnIL-1R can activate the Toll signaling pathway in the ovary by directly recognizing LPS and PGN through its IG domain, thereby contributing to the immune response in the ovary of M. nipponense.

Immunostimulant effects of Pituitary Adenylate Cyclase-Activating Polypeptide and double-stranded (ds)RNA in Orconectes propinquus

Disease outbreaks in crustacean aquaculture caused by opportunistic and obligate pathogens cause severe economic losses to the industry. Antibiotics are frequently used as prophylactic treatments worldwide, although its overuse and misuse has led to microbial resistance, which has driven the search for novel molecules with immunostimulant and antibacterial activities. Antimicrobial peptides (AMP) and double-stranded (ds)RNAs constitute promising immunostimulants in the fight against infectious diseases in aquaculture. Scientists have made significant progress in testing these molecules in aquatic organisms as potential candidates for replacing conventional antibiotics. However, most studies have been conducted in teleost fish, thus little is known about the immunostimulatory effects in crustaceans, especially in freshwater crayfishes. Consequently, in the present work, we evaluate the immunomodulatory effects of the AMP Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) and high molecular weight (HMW) Poly (I:C) in the northern clearwater crayfish Orconectes propinquus. Two bioassays were conducted to evaluate the effects of different doses of PACAP and Poly (I:C) HMW, different administration routes, as well as the effects of the combined treatment on the crayfish immune system. Results showed the immunostimulatory role of PACAP and Poly (I:C) HMW with effects depending on the dose, the site of injection and the treatment assessed. These findings offer new insights into the crayfish immune system and contribute to the development of effective broad-spectrum immune therapies in aquaculture.

The evolutionary adaptation of shrimp hemocyanin subtypes and the consequences on their structure and functions

Hemocyanin is the main respiratory protein of arthropods and is formed by hexameric and/or oligomeric subunits. Due to changes in the living environment and gene rearrangement, various hemocyanin subtypes and subunits evolved in crustaceans. This paper reviews the various hemocyanin subtypes and isoforms in shrimp and analyses published genomic data of sixteen hemocyanin family genes from Litopenaeus vannamei to explore the evolution of hemocyanin genes, subunits, and protein structure. Analysis of hemocyanin subtypes distribution and structure in various tissues was also performed and related to multiple and tissue-specific functions, i.e., immunological activity, immune signaling, phenoloxidase activity, modulation of microbiota homeostasis, and energy metabolism. The functional diversity of shrimp hemocyanin due to molecular polymorphism, transcriptional regulation, alternative splicing, degradation into functional peptides, interaction with other proteins or genes, and structural differences will also be highlighted for future research. Inferences would be drawn from other crustaceans to explain how evolution has changed the structure-function of hemocyanin and its implication for evolutionary research into the multifunctionality of hemocyanin and other related proteins in shrimp.

Temporal dynamics of the immune response in Astacus astacus (Linnaeus, 1758) challenged with Aphanomyces astaci Schikora, 1906

One of the main drivers of biodiversity loss in freshwater ecosystems are alien invasive species. In Europe, pathogen Aphanomyces astaci Schikora, 1906, is considered as one of the most problematic invasive species, as its introduction caused the severe decimation of the European freshwater crayfish stocks. The most affected are the populations of noble crayfish, keystone species native to European freshwaters. Unfortunately, even after decades of research, we do not understand the temporal dynamics of the noble crayfish immune response during Ap. astaci infection. Here, we studied the changes in the immune response of the noble crayfish during a time course challenge with a highly virulent strain of Ap. astaci. We recorded gross symptoms of the disease, changes in the total haemocyte count (THC), gene expression profiles of putative immune response regulators and pathogen load. Additionally, we conducted a preliminary histological analysis of the pathogen dissemination in host tissues. Based on the occurrence of symptoms we propose three stages in the crayfish plague disease progression: asymptomatic stage, symptomatic stage, and finally death of infected individual. Furthermore, based on the qPCR analysis we could differentiate three Ap. astaci growth phases: initial lag phase, followed by exponential growth phase and finally sporulation phase. We observed that all measured immune response parameters were significantly correlated to the observed increase in the pathogen load (qPCR). Altogether, our results point to the absence of a successful immune response in the noble crayfish to a challenge with a highly virulent strain of Ap. astaci. The noble crayfish immune system was not able to suppress the growth of the intruding pathogen. In general, our observations have to be considered in the context of the specific combination of crayfish plague pathogen virulence and disease resistance of the challenged crayfish population, which defines the temporal dynamics of their interaction.

Research progress of pattern recognition receptors in red swamp crayfish (Procambarus clarkii)

Though Procambarus clarkii (red swamp crayfish) is a lower invertebrate, it has nonetheless developed a complex innate immune system. The crayfish farming industry has suffered considerable economic losses in recent years as a consequence of bacterial and viral diseases. Hence, perhaps the most effective ways to prevent microbial infections in P. clarkii are to examine and elucidate its innate immunity. The first step in the immune response is to recognize pathogen-associated molecular patterns (PAMPs) through pattern recognition receptors (PRRs). PRRs are expressed mainly on immune cell surfaces and recognize at least one PAMP. Thence, downstream immune responses are activated and pathogens are phagocytosed. To date, the PRRs identified in P. clarkii include Toll-like receptors (TLRs), lectins, fibrinogen-related proteins (FREPs), and β-1,3-glucan-binding proteins (BGRPs). The present review addresses recent progress in research on PRRs and aims to provide guidance for improving immunity and preventing and treating infectious diseases in P. clarkii.

Cellular responses in crustaceans under white spot syndrome virus infection

Innate immunity plays the most important system responsible for protecting crustaceans against invading pathogens. White spot syndrome virus (WSSV) is considered a serious pathogen in crustaceans with high cumulative mortality and morbidity in infected animals. Understanding the mechanism of the response of hosts to WSSV infection is necessary, which is useful for effective prevention in controlling infection. In this review, we summarize the participation of signaling pathways (toll, immune deficiency, JAK/STAT, endocytosis, mitogen-activated protein kinase, PI3K/Akt/mTOR, cGAS-STING, Wingless/Integrated signal transduction, and prophenoloxidase (proPO) cascade) and the activity of cells (apoptosis, autophagy, as well as, reactive oxygen species and antioxidant enzymes) in the cellular-mediated immune response of crustaceans during WSSV infection. The information presented in this current review is important for a better understanding of the mechanism of the response of hosts to pathogens. Additionally, this provides a piece of basic knowledge for discovering approaches to strengthen the immune system and resistance of cultured animals against viral infections.

Microplastics in feed cause sublethal changes in the intestinal microbiota and a non-specific immune response indicator of the freshwater crayfish Procambarus clarkii (Decapoda: Cambaridae)

Microplastics (MP) are a hazardous pollutant of global concern that threatens aquatic ecosystems and public health. We used the invasive, cosmopolitan, and environmentally versatile red swamp crayfish Procambarus clarkii as a model to study the effects of MP on the intestinal microbiome. Crayfish collected from the environment were compared with specimens exposed to recycled Polyethylene terephthalate (rPET) MP in feed (30%) for 96 h in the laboratory and a control group. We analyzed the 16S rRNA of the intestinal bacteria by PCR-DGGE and high-throughput sequencing. MP exposure caused dysbiosis of the intestinal microbiota, with an increase in Alphaproteobacteria and Actinobacteria. We detected higher abundance of opportunistic genera such as Klebsiella, Acinetobacter, Hydromonas, Pseudomonas, Gemmobacter, and Enterobacter on MP fed organisms. Moreover, MP exposure reduced the abundance of Clostridia and Bateroidetes, which are important for immune system development and pathogen prevention. Furthermore, MP exposure decreased the phenoloxidase (PO) immune response in crayfish. There was a significant difference in the richness of intestinal bacterial communities after consumption of food contaminated with MP, likely increasing the abundance of opportunistic bacteria in the intestinal microbiota. Our results suggest that MP alter the gut microbial composition and impair the health of P. clarkii.

Crayfish Research: A Global Scientometric Analysis Using CiteSpace

A scientometric analysis was conducted to investigate the trends and development of crayfish research in terms of literature published, author, affiliation, and countries' collaborative networks, as well as the co-citation dataset (e.g., author, article, and keywords). The study analyzed 12,039 bibliographic datasets from the Web of Science, using CiteSpace as a tool for the co-citation analysis. The study revealed extraordinary increases in publication trends, with a total of 21,329 authors involved in approximately 80% of countries around the world (163/195) having conducted crayfish research. Unsurprisingly, countries such as the USA and China, followed by European countries, were among the top countries that have published crayfish-related studies. The findings also indicated that "invasive crayfish" was the world's top keyword for crayfish research. Crayfish species are important for both environmental sustainability (invasiveness and species composition) and social wellbeing (aquaculture), which provides directions for research, philanthropic, academic, government, and non-government organizations regarding how to invest limited resources into policies, programs, and research towards the future management of this species. Our study concluded that strategic collaboration among authors, institutions, and countries would be vital to tackle the issue of invasive crayfish species around the world.

Effectiveness of various cacao pod husk extraction byproducts in promoting growth and immunocompetence in Litopenaeus vannamei

Extracts from plant products can promote growth, can act as immunostimulants, and have antibacterial and antiparasitic properties. These extracts can be used as alternatives to the chemical treatments commonly used to prevent and control disease in aquatic species. Research on the subject has focused on identifying invasive plants or agricultural waste products that can be used as immunostimulants. The present study further identified an optimal means of extracting pectin from cacao pod husks to promote growth performance and immunocompetence in Litopenaeus vannamei that would both reduce production costs and enable waste recycling. The byproducts of pectin extraction from cacao pod husks, that is, dried cacao pod husk powder (DCP), steamed DCP (sDCP), hot water-treated cacao pod husk powder (HCP), hot water-treated cacao pod husk supernatant (HCS), and cacao pod husk pectin (CPH pectin), were used to create five experimental diets, which were administered to five groups. The control group was fed a basal diet. The growth and immunocompetence of the shrimp were determined after 30, 60, 90 and 120 days of feeding. To identify the most cost-effective means of obtaining dried cacao pod husks, this study firstly determined the costs and effectiveness of the sun-drying, dehumidification, and heated-wind drying techniques. According to the results of growth performance, the CPH pectin group had higher survival but lower weight gain than the DCP, sDCP, HCP, and HCS groups did. At 30, 60, and 90 days, the clearance efficiency of the experimental groups was higher than that of the control group. At 60 days, the experimental groups had significantly higher phagocytic activity than the control group did. However, at 30 and 90 days the HCP, HCS and CPH pectin group had higher phagocytic activity. The total hemocyte count, differential hemocyte count, phenoloxidase activity, and respiratory bursts of the CPH pectin group were higher at 30 days but the same as those of the control group at 60 and 90 days. After 120 days of feeding trial, the resistance of L. vannamei fed with diets containing byproducts of pectin extraction from cacao pod husks significantly enhanced compared to that in BD group when they were infected with Vibrio aliginolyticus for 168 h, and the related higher survival rate can be observed in HCP, HCS and CPH pectin groups. The study findings suggest that diet-administered HCP and HCS have long-term immunostimulant potential and that CPH pectin has potential in the early stages of feeding. In addition, when heated air drying was employed, a moisture level of below 10% was obtained within 12 h. The results of this study indicate that adding HCP obtained from heated air-dried cacao pod husks to the feed of L. vannamei is the most cost-effective and sustainable means of promoting long-term growth performance and immunocompetence in the species.

Cherax quadricarinatus Resistant to Chequa iflavirus: A Pilot Study

High mortalities of redclaw crayfish (Cherax quadricarinatus) were reported from northern Queensland farms, mainly attributed to two viruses, Chequa iflavirus and Athtab bunyavirus. From a research population of redclaw crayfish with these pre-existing viral infections, five individuals were found uninfected by Chequa iflavirus but infected with Athtab bunyavirus. A pilot study was designed to examine if progeny crayfish from this cohort were resistant to infections by Chequa iflavirus. Two experiments measured changes in viral load with RT-qPCR. Seven donors, four negative controls and six crayfish injected with a purified virus or saline were used. In Experiment 1, the purified viral inoculum was injected into the crayfish, and they were bled 14 days post-injection (dpi). In Experiment 2, haemolymph containing the viruses was injected into the same crayfish and they were bled at 24 hpi, 48 hpi, 7 dpi and 14 dpi. In Exp. 1, the crayfish cleared Chequa iflavirus infections within 14 dpi, while in Exp. 2, it was within 24 hpi. One mortality was observed, but that crayfish had cleared the virus before dying. The number of copies of Athtab bunyavirus and the weights of the crayfish did not differ significantly (p > 0.05) between the control and injected crayfish. Histology of crayfish all showed that the haemolymph vessels were clear of granulomas, suggesting no bacterial involvement. There was no melanisation in the gill tissue of control crayfish, but it was prominent in virus-injected crayfish. Neither group had haemocytic infiltration of the muscle fibres. Anti-viral immune mechanisms of RNA interference and Cherax quadricarinatus Down Syndrome Cell Adhesion Molecule (DSCAM) are hypothesised to be involved in viral clearance. We conclude that these crayfish were resistant to Chequa iflavirus infections and could be commercially exploited by aquaculturists as a nuclear breeding stock if numbers are increased over time.

Growth and Welfare Status of Giant Freshwater Prawn (Macrobrachium rosenbergii) Post-Larvae Reared in Aquaponic Systems and Fed Diets including Enriched Black Soldier Fly (Hermetia illucens) Prepupae Meal

Due to the limited application of insect meal in giant freshwater prawn (Macrobrachium rosenbergii) culture, the present study aimed to (i) produce spirulina-enriched full-fat black soldier fly (Hermetia illucens) prepupae meal (HM) and (ii) test, for the first time, two experimental diets characterized by 3% or 20% of fish meal and fish oil replacement with full-fat HM (HM3 and HM20, respectively) on M. rosenbergii post-larvae during a 60-day feeding trial conducted in aquaponic systems. The experimental diets did not negatively affect survival rates or growth. The use of spirulina-enriched HM resulted in a progressive increase in α-tocopherol and carotenoids in HM3 and HM20 diets that possibly played a crucial role in preserving prawn muscle-quality traits. The massive presence of lipid droplets in R cells in all the experimental groups reflected a proper nutrient provision and evidenced the necessity to store energy for molting. The increased number of B cells in the HM3 and HM20 groups could be related to the different compositions of the lipid fraction among the experimental diets instead of a nutrient absorption impairment caused by chitin. Finally, the expression of the immune response and stress markers confirmed that the experimental diets did not affect the welfare status of M. rosenbergii post-larvae.

Hallmarks of crustacean immune hemocytes at single-cell resolution

In invertebrates, hemocytes are the key factors in innate immunity. However, the types of invertebrate immune hemocytes are unclassified due to the limitation of morphological classification. To determine the immune hemocytes of crustaceans, the heterogeneity of hemocytes of shrimp Marsupenaeus japonicus and crayfish Procambarus clarkii, two representative crustacean species, were characterized in this study. The results of single-cell RNA sequencing indicated that shrimp and crayfish contained 11 and 12 types of hemocytes, respectively. Each of different types of hemocytes specifically expressed the potential marker genes. Based on the responses of shrimp and crayfish to the infection of white spot syndrome virus (WSSV) and the challenge of lipopolysaccharide (LPS), four types of immune hemocytes of crustaceans were classified, including semi-granular hemocytes involved in antimicrobial peptide production, granular hemocytes responsible for the production of antimicrobial peptides, hemocytes related to cell proliferation and hemocytes in immunity-activated state. Therefore, our study provided the first classification of crustacean hemocytes as well as of immune hemocytes of crustaceans at the single-cell resolution, which would be helpful to understand the innate immunity of invertebrates.

Effects of Dietary Pectin and Lactobacillus salivarius ATCC 11741 on Growth Performance, Immunocompetence, Gut Microbiota, Antioxidant Capacity, and Disease Resistance in Narrow-Clawed Crayfish, Postantacus leptodactylus

The present study was conducted to clarify the effects of Lactobacillus salivarius (LS) ATCC 11741 and pectin (PE) on growth performance, digestive enzymes activity, gut microbiota composition, immune parameters, antioxidant defense as well as disease resistance against Aeromonas hydrophila in narrow-clawed crayfish, Postantacus leptodactylus. During 18 weeks trial feeding, 525 narrow-clawed crayfish juvenile (8.07 ± 0.1 g) fed with seven experimental diets including control (basal diet), LS1 (1 × 10⁷ CFU/g), LS2 (1 × 109 CFU/g), PE1 (5 g/kg), PE2 (10 g/kg), LS1PE1 (1 × 10⁷ CFU/g +5 g/kg), and LS2PE2 (1 × 109 CFU/g +10 g/kg). After 18 weeks, growth parameters (final weight, weight gain, and specific growth rate) and feed conversion rate were significantly improved in all treatments (P < 0.05). Besides, diets incorporated with LS1PE1 and LS2PE2 significantly increased the activity of amylase and protease enzymes compared to LS1, LS2, and control groups (P < 0.05). Microbiological analyses revealed that the total heterotrophic bacteria count (TVC) and lactic acid bacteria (LAB) of narrow-clawed crayfish fed diets containing LS1, LS2, LS1PE1, and LS2PE2 were higher than control group. The highest total haemocyte count (THC), large-granular (LGC) and semigranular cells (SGC) count, and hyaline count (HC) was obtained in LS1PE1 (P < 0.05). Similarly, higher immunity activity (lysozyme (LYZ), phenoloxidase (PO), nitroxidesynthetase (NOs), and alkaline phosphatase (AKP)) observed in the LS1PE1 treatment compared to the control group (P < 0.05). The glutathione peroxidase (GPx) and superoxide dismutase (SOD) activity remarkably enhanced in LS1PE1 and LS2PE2, while malondialdehyde (MDA) content reduced in these two treatments. In addition, specimens belonging to LS1, LS2, PE2, LS1PE1, and LS2PE2 groups presented higher resistance against A. hydrophila compared to the control group. In conclusion, feeding narrow-clawed crayfish with synbiotic had higher efficiency on growth parameters, immunocompetence, and disease resistance compared to single consumption of prebiotics and probiotics.

Integrated analysis of mRNA and microRNA transcriptome related to immunity and autophagy in shrimp hemocytes infected with Spiroplasma eriocheiris

In recent years, the industry in charge of the cultivation of Macrobrachium nipponense (M.nipponense) has suffered significant economic losses due to an infectious pathogen called Spiroplasma eriocheiris (S.eriocheiris). There has therefore been a need to identify the key immune and autophagy genes that respond to M.nipponense's infection with S. eriocheiris to analyze its immune response mechanism and the regulation of related microRNAs (miRNAs). In this study, the mRNA and miRNA transcriptome of M.nipponense's hemocytes were analyzed at different stages of infection. This analysis employed the second and third-generation sequencing technologies. In the mRNA transcriptome, 1656 genes were expressed in healthy and susceptible M.nipponense. 892 of these were significantly up-regulated, while 764 were down-regulated. 118 genes with significant differences in autophagy, endocytosis, lysosome, Toll, IMD, and VEGF pathways were obtained from the transcriptome. In the miRNA transcriptome, 312 miRNAs (Conserved: 112, PN-type: 18, PC-type: 182) were sequenced. 74 were significantly up-regulated, and 57 were down-regulated. There were 25 miRNAs involved in regulating the Toll and IMD pathways, 41 in endocytosis, 30 in lysosome, and 12 in the VEGF pathway. An integrated analysis of immune-related miRNAs and mRNAs showed that miRNAs with significant differences (P < 0.05) such as ame-miR-29b-3p, dpu-miR-1and PC-3p-945_4074, had corresponding regulatory relationships with 118 important immune genes such as Relish, Dorsal, Caspase-3, and NF-κB. This study obtained the key immune and autophagy-related genes and corresponding regulatory miRNAs in M. nipponense's hemocytes in response to an infection by S.eriocheiris. The results can provide vital data that further reveals the defense mechanism of M.nipponense's immune system against S.eriocheiris. It can also help further comprehension and interpretation of M.nipponense's resistance mechanism to the invading S.eriocheiris, and provide molecular research information for the realization of host-directed therapies (HDT) for M.nipponense.

The amphipod Parhyale hawaiensis as a promising model in ecotoxicology

Near-shore marine/estuarine environments play an important role in the functioning of the marine ecosystem and are extremely vulnerable to the presence of chemical pollution. The ability to investigate the effects of pollution is limited by a lack of model organisms for which sufficient ecotoxicological information is available, and this is particularly true for tropical regions. The circumtropical marine amphipod Parhyale hawaiensis has become an important model organism in various disciplines, and here we summarize the scientific literature regarding the emergence of this model within ecotoxicology. P. hawaiensis is easily cultured in the laboratory and standardized ecotoxicity protocols have been developed and refined (e.g., miniaturized), and effects of toxicants on acute toxicity (Cd, Cu, Zn, Ag, ammonia, dyes, pesticides, environmental samples), genotoxicity as comet assay/micronuclei, and gene expression (Ag ion and Ag nanoparticles) and regeneration (pesticides) have been published. Methods for determination of internal concentrations of metals (Cu and Ag) and organic substances (synthetic dye) in hemolymph were successfully developed providing sources for the establishment of toxicokinetics models in aquatic amphipods. Protocols to evaluate reproduction and growth, for testing immune responses and DNA damage in germ cells are under way. The sensitivity of P. hawaiensis, measured as 50% lethal concentration (LC50), is in the same range as other amphipods. The combination of feasibility to culture P. hawaiensis in laboratory, the recent protocols for ecotoxicity evaluation and the rapidly expanding knowledge on its biology make it especially attractive as a model organism and promising tool for risk assessment evaluations in tropical environments.

Immune Defense in Hypoxic Waters: Impacts of CO2 Acidification

AbstractPeriodic episodes of low oxygen (hypoxia) and elevated CO₂ (hypercapnia) accompanied by low pH occur naturally in estuarine environments. Under the influence of climate change, the geographic range and intensity of hypoxia and hypercapnic hypoxia are predicted to increase, potentially jeopardizing the survival of economically and ecologically important organisms that use estuaries as habitat and nursery grounds. In this review we synthesize data from published studies that evaluate the impact of hypoxia and hypercapnic hypoxia on the ability of crustaceans and bivalve molluscs to defend themselves against potential microbial pathogens. Available data indicate that hypoxia generally has suppressive effects on host immunity against bacterial pathogens as measured by in vitro and in vivo assays. Few studies have documented the effects of hypercapnic hypoxia on crustaceans or bivalve immune defense, with a range of outcomes suggesting that added CO₂ might have additive, negative, or no interactions with the effects of hypoxia alone. This synthesis points to the need for more partial pressure of O₂ × low pH factorial design experiments and recommends the development of new host∶pathogen challenge models incorporating natural transmission of a wide range of viruses, bacteria, and parasites, along with novel in vivo tracking systems that better quantify how pathogens interact with their hosts in real time under laboratory and field conditions.

Molecular markers for hemocyte subpopulations in crayfish Cherax quadricarinatus

Semigranular cells (SGCs) and granular cells (GCs) are two dominant groups of circulating hemocytes in crayfish Cherax quadricarinatus. Molecular markers are required for the clear classification of the hemocytes and the research of their function and differentiation. In this study, we compared the protein content of GCs and SGCs by using two workflows: one-dimensional gel electrophoresis followed by LC-MS/MS and in-solution digestion of cell lysate followed by LC-MS/MS. Cell type-specific proteins were identified, and their expression in SGCs and GCs was further investigated by RT-PCR, Western blotting, and immunofluorescence analysis. Three molecular markers for GCs (peroxinectin, a mannose-binding protein, and prophenoloxidase-activating enzyme 2a) and three molecular markers for SGCs (a vitelline membrane outer layer protein I-like protein, a C-type lectin, and a peptidase) were identified. The application of some of the markers in Eriocheir sinensis was also analyzed. These molecular markers are useful tools for the research of crustaceans hemocytes.

Shrimp bacterial and parasitic disease listed in the OIE: A review

Shrimp aquaculture industry has steadily increased with demand and development of aquaculture technology. In recent years, frequent diseases have become a major risk factor for shrimp aquaculture, such as a drastically reduced the production of shrimp and causing national economic loss. Among them, shrimp bacterial diseases such as hepatopancreatic necrosis disease (AHPND) and necrotizing hepatopancreatitis (NHP-B) and parasitic disease such as Aphanomyces astaci (crayfish plague) are emerging and evolving into new types. OIE (World Organization for Animal Health) regularly updates information on diseases in the Aquatic Code and Aquatic Manual, but in-depth information on the shrimp diseases are lacking. Therefore, the purpose of this review is to provide information necessary for the response and prevention of shrimp diseases by understanding the characteristics and diagnosis of shrimp diseases designated by OIE.

Changes in the Immunity, Histopathology, and Metabolism of Crayfish (Procambarus clarkii) in Response to Drought

Freshwater ecosystems are among the most threatened ecosystems on Earth. The freshwater biodiversity crisis has caused widespread global concern. Drought as one of the factors causing freshwater biodiversity is still poorly understood. Crayfish is often used in academic research as a biological indicator. In this study, flow cytometry, hematoxylin-eosin staining, and untargeted metabolomics were used to analyze the immune function, histopathology, and metabolism of crayfish under drought conditions. After drought exposure, the total hemocytes count (THC) was significantly decreased (from 8.9 × 105 mL−1 in the control group to 2.2 × 105 mL−1 at day 5). Phagocytosis decreased by 66% after 5 days of drought. The level of reactive oxygen species (ROS) in the hepatopancreas was upregulated. Moreover, histological disorder and metabolism changes in the hepatopancreas were obvious. These results indicate that drought suppresses immune function, disrupts the balance of oxidative and antioxidative systems, and induces tissue damage and metabolic changes in crayfish.

Differential white spot syndrome virus-binding proteins in two hemocyte subpopulations of Chinese shrimp (Fenneropenaeus chinensis)

A number of white spot syndrome virus (WSSV)-binding proteins have been identified previously in the hemocytes of Fenneropenaeus chinensis. In order to further investigate the differential WSSV-binding proteins in hemocyte subpopulations, granular hemocytes and hyalinocytes were sorted from WSSV-infected shrimp by immunomagnetic bead (IMB) method. The results of ELISA and immuno-dot blot assay showed that the WSSV-binding activity of granular hemocytes proteins was much stronger than that of hyalinocytes proteins. And the percentage of WSSV-positive granular hemocytes was significantly higher than that of hyalinocytes post WSSV infection, indicating that granular hemocytes were more susceptible to WSSV infection. Moreover, a total of 9 WSSV-binding proteins were successfully identified in granular hemocytes and hyalinocytes by two-dimensional virus overlay protein binding assay (2D-VOPBA) and MALDI-TOF MS analysis, of which 3 binding proteins (arginine kinase, protease 1 and transglutaminase) existing in both hyalinocytes and granular hemocytes and 6 proteins (F₁ATP synthase β-chain, hnRNPs, GAPDH, RACK1, β-actin and cellular retinoic acid) detected only in granular hemocytes. Among these identified WSSV-binding proteins, the transglutaminase (TG) was further recombinantly expressed, and the recombinant TG could be bound with WSSV. Subsequently, quantitative real-time PCR analysis showed that differential expression levels of WSSV-binding proteins were observed in granular hemocytes and hyalinocytes. The results of this study revealed that the WSSV-binding proteins were differentially expressed in granular hemocytes and hyalinocytes, which provided a deeper insight into the interaction between WSSV and hemocyte subpopulations.

Synbiotic combination of prebiotic, cacao pod husk pectin and probiotic, Lactobacillus plantarum, improve the immunocompetence and growth of Litopenaeus vannamei

To reach the sustainable development goals on waste recycling, cacao pod husk (CPH), produced as an agricultural waste byproduct during the cacao bean processing was applied to manufacture CPH pectin for developing the potential for diverse application in aquaculture, minimizing CPH impact to the environment and bringing benefits to the agriculture and aquaculture industries. In this study, CPH pectin (5 g/kg diet) and Lactobacillus plantarum (LP; 10¹⁰ cfu/kg diet) were separately introduced to the diets of Litopenaeus vannamei for a 56-day feeding trial, and two synbiotic combinations of CPH pectin and LP (CPH pectin at 5 g/kg diet + LP at 10⁷ cfu/kg diet or at 10¹⁰ cfu/kg diet) were also conducted. After the 56-day feeding trial, significantly elevated percent weight gain, percent length gains and feeding efficiency in L. vannamei were only observed in synbiotic combination of CPH pectin at 5 g/kg diet and LP at 10⁷ cfu/kg diet treatment, and the remainder of the treatments remained consistently similar to the control. Significantly increases in total haemocyte count, granular cells, phenoloxidase activity, and respiratory bursts were observed in L. vannamei fed with synbiotics at 7-28 days of feeding, accompanied by significant promotion of phagocytic activity and clearance efficiency in response to V. alginolyticus challenge during 56 days of feeding trial. Furthermore, at the end of the 56 days of feeding trial, shrimp receiving CPH pectin and/or LP treatments showed a significantly higher survival ratio against V. alginolyticus infection and hypothermal stress. It was therefore concluded that CPH pectin or LP was confirmed as an immunostimulant for L. vannamei to trigger immunocompetence through oral administration without negative effects within 56 days of feeding trial, and the synbiotic combination of CPH pectin and LP exhibited complementary and synergistic effects on growth performance and immunocompetence in L. vannamei.

Lytic Polysaccharide Monooxygenases as Chitin-Specific Virulence Factors in Crayfish Plague

The oomycete pathogen Aphanomyces astaci, also known as “crayfish plague”, is an obligate fungal-like parasite of freshwater crustaceans and is considered responsible for the ongoing decline of native European crayfish populations. A. astaci is thought to secrete a wide array of effectors and enzymes that facilitate infection, however their molecular mechanisms have been poorly characterized. Here, we report the identification of AA15 lytic polysaccharide monooxygenases (LPMOs) as a new group of secreted virulence factors in A. astaci. We show that this enzyme family has greatly expanded in A. astaci compared to all other oomycetes, and that it may facilitate infection through oxidative degradation of crystalline chitin, the most abundant polysaccharide found in the crustacean exoskeleton. These findings reveal new roles for LPMOs in animal–pathogen interactions, and could help inform future strategies for the protection of farmed and endangered species.