Expression of immune-related genes in rohu Labeo rohita (Hamilton) by experimental freshwater lice Argulus siamensis (Wilson) infection

Efficacy of quercetin in ameliorating hypoxia-induced hematological and histopathological alterations in rohu Labeo rohita

Hypoxia, a major issue in aquatic ecosystems, in special reference to climate change, and exacerbated by anthropogenic activities. It is causing slow growth, disease outbreaks, and mortality in finfish and shellfish. Therefore, adaptation to lowering oxygen levels through supplementation of herbs or their extracts in diets is imperative. In this study, hypoxia was simulated in controlled conditions with quercetin-enriched diets. Quercetin is a plant pigment (flavonol) possessing anti-oxidant property and is present in vegetables, leaves, seeds, pulses, and fruits. The experiment was conducted on rohu Labeo rohita, which is most widely cultured in India. There were four treatments including T1 (Normoxia: > 5 ppm dissolved oxygen; DO2), T2 (hypoxia: 3-4 ppm DO2), T3 (hypoxia + 50 mg quercetin/kg diet), and T4 (hypoxia + 100 mg quercetin/kg diet). The study was conducted for 30 days, and water quality was measured regularly. The results revealed that the hematological parameters were negatively affected. The tissue micro-architecture illustrated the impairment through degeneration of neurons in the brain, increased pigmentation as melanosis in the kidney, increased thickness of primary lamellae in the gills, and dilatations of sinusoids in the liver in hypoxia groups, while quercetin-enriched diets improved the hematological and histomorphological parameters. The results confirm the utility of hematological and histopathological tools as biomarkers and reflect the possible threats of hypoxia on fish. In conclusion, quercetin in diets appeared to show resistance towards chronic hypoxia by restoring the structure and functions of the vital organs towards normalcy and could be recommended as a potential ameliorative agent.

A comprehensive review on the dynamic role of toll-like receptors (TLRs) in frontier aquaculture research and as a promising avenue for fish disease management

Toll-like receptors (TLRs) represent a conserved group of germline-encoded pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs) and play a crucial role in inducing the broadly acting innate immune response against pathogens. In recent years, the detection of 21 different TLR types in various fish species has sparked interest in exploring the potential of TLRs as targets for boosting immunity and disease resistance in fish. This comprehensive review offers the latest insights into the diverse facets of fish TLRs, highlighting their history, classification, architectural insights through 3D modelling, ligands recognition, signalling pathways, crosstalk, and expression patterns at various developmental stages. It provides an exhaustive account of the distinct TLRs induced during the invasion of specific pathogens in various fish species and delves into the disparities between fish TLRs and their mammalian counterparts, highlighting the specific contribution of TLRs to the immune response in fish. Although various facets of TLRs in some fish, shellfish, and molluscs have been described, the role of TLRs in several other aquatic organisms still remained as potential gaps. Overall, this article outlines frontier aquaculture research in advancing the knowledge of fish immune systems for the proper management of piscine maladies.

Oxidative stress, gene expression and histopathology of cultured gilthead sea bream (Sparus aurata) naturally co-infected with Ergasilus sieboldi and Vibrio alginolyticus

BACKGROUND

Parasitic and bacterial co-infections have been associated with increasing fish mortalities and severe economic losses in aquaculture through the past three decades. The aim of this study was to evaluate the oxidative stress, histopathology, and immune gene expression profile of gilthead sea bream (Sparus aurata) co-infected with Ergasilus sieboldi and Vibrio alginolyticus.

RESULTS

Vibrio alginolyticus and Ergasilus sieboldi were identified using 16 S rRNA and 28 S rRNA sequencing, respectively. The collagenase virulence gene was found in all Vibrio alginolyticus isolates, and the multiple antimicrobial resistance index ranged from 0.286 to 0.857. Oxidant-antioxidant parameters in the gills, skin, and muscles of naturally infected fish revealed increased lipid peroxidation levels and a decrease in catalase and glutathione antioxidant activities. Moreover, naturally co-infected gilthead sea bream exhibited substantial up-regulation of il-1β, tnf-α, and cyp1a1. Ergasilus sieboldi encircled gill lamellae with its second antennae, exhibited severe gill architectural deformation with extensive eosinophilic granular cell infiltration. Vibrio alginolyticus infection caused skin and muscle necrosis in gilthead sea bream.

CONCLUSION

This study described some details about the gill, skin and muscle tissue defense mechanisms of gilthead sea bream against Ergasilus sieboldi and Vibrio alginolyticus co-infections. The prevalence of co-infections was 100%, and no resistant fish were detected. These co-infections imbalance the health status of the fish by hampering the oxidant-antioxidant mechanisms and proinflammatory/inflammatory immune genes to a more detrimental side. Our results suggest that simultaneous screening for bacterial and parasitic pathogens should be considered.

Unraveling the host-parasite interaction: immune response in Oreochromis mossambicus to Cymothoa eremita (Isopoda, Cymothoidae) infection

The host immune response in Oreochromis mossambicus during natural infection with the isopod Cymothoa eremita was investigated. The naturally infected fishes were examined for enzyme profile, viz., respiratory burst activity (RBA), myeloperoxidase activity (MPO), and expression of immune-related genes, viz., toll-like receptor 22 (TLR 22), interleukin-1β (IL-1β), tumor necrosis factor α (TNF-α), complement component (C3), chemokine (CXCa), and β-actin in tissues of various organs (buccal cavity, gills and anterior kidney). Significant reduction (P < 0.05) in RBA and MPO was observed in the parasite-infected fishes when compared to the uninfected control fishes. In the buccal cavity, the expression of the immune-related genes was significantly (P < 0.05) upregulated, whereas all the genes except IL-1β were significantly (P < 0.05) upregulated in the anterior kidney. In the case of gill tissue, the expressed genes showed a varied type of regulation. The immunological responses in O. mossambicus during isopod infection have not been investigated in detail so far, and this is the first study unveiling such insights. Hence, this study will help to improve our molecular understanding of the host-immune response to parasitic isopod infection.

Stability evaluation and validation of appropriate reference genes for real-time PCR expression analysis of immune genes in the rohu (Labeo rohita) skin following argulosis

Argulosis is one of the most unrestrained economically significant freshwater fish ectoparasitic diseases. Proper selection or normalization of the best reference gene governs the accuracy of results of gene expression studies using real-time PCR. Earlier studies in rohu carp (Labeo rohita) have used reference genes without proper validation. Here, seven candidate reference genes viz., acidic ribosomal protein (ARP0), glyceraldehyde 3-phosphate dehydrogenase, RNA polymerase II (RPo), elongation factor1α (EF1α), α- tubulin (AT), ribosomal protein L 10, and β-actin were evaluated using four algorithms (geNorm, BestKeeper, NormFinder and ∆Ct) followed by a comprehensive gene expression analysis using skin tissue of rohu at varied time points of experimental Argulus siamensis infection. ARP0 and EF1α were found to be the most stable whereas RPo and AT were considered as least stable genes based on basal expression level and variation in expression levels. Validation of candidate reference genes was undertaken by looking into the expression of six immune-related genes using the two most stable and two least stable genes as housekeeping genes in Argulus-infected rohu skin at different time points of infection. An increased expression of immune genes indicated the role of inflammation and the immune modulation process at the site of attachment of parasites in governing infection.

Antiparasitic potentiality of ethanol and methanol extracts of Azadirachta indica leaf for eggs and copepodid stage of Argulus japonicus: in vitro study

In the present study, eggs and copepodid stages of Argulus japonicus were treated with ethanol and methanol extract of Azadirachta indica (neem) leaf and its antiparasitic efficacy (AE %) was determined. The experiments were performed in triplicate along with the positive (2% DMSO) and negative (without DMSO and extract) control groups. The reduced cumulative hatching percentage of eggs by 13% (in ethanolic) and 17% (in methanolic) extract of neem leaf at 1.5 g L^-1 was obtained during 15-day exposure compared to the control group showing 70-85% eggs hatching. The AE of 100% for ethanolic and 91.66% for methanolic extract against the copepodid stage was found at 1.25 and 1.5 g L^-1 respectively in 6 h. The histological analysis of the eggs showed the undifferentiated decaying mass of cells with extensively damaged eggs when treated with ethanolic extract of neem leaf. Further, severe degeneration in the branchial region, digestive tract and eye cells was observed in the copepodids treated with ethanol extract than the methanol extract. The terpenoids a potential antiparasitic compound of ethanolic extract produced more AE than the methanolic extract. Thus, the ethanolic extract of neem leaf can be potentially utilized as a natural parasiticide to disrupt the egg and other life phases of A. japonicus.

Recombinant outer membrane protein OmpC induces protective immunity against Aeromonashydrophila infection in Labeorohita

Aeromonashydrophila is an opportunistic pathogen that causes enormous loss to aquaculture industry. The outer membrane proteins of Aeromonas help in bacterium-host interaction, and are considered to be potential vaccine candidates. In the present study, we evaluated immunogenicity and protective efficacy of recombinant OmpC (rOmpC) of A. hydrophila in Indian major carp, Labeorohita. The rOmpC-vaccinated fish produced specific anti-rOmpC antibodies with a significant antibody titer, and the antisera could specifically detect the rOmpC in the cell lysates of Escherichia coli expressing rOmpC and cross-react with different Aeromonas lysates, indicating the suitability of the anti-rOmpC antisera to detect Aeromonas infection. A significant increase was noted in ceruloplasmin level, myeloperoxidase and anti-protease activities in transient and temporal manner the sera of the rOmpC-immunized fish as compared to PBS-control fish. Higher agglutination- and hemolytic activity titers in the anti-rOmpC antisera indicate stimulation of innate immunity. Expression of immune-related genes comprising various acute phase proteins, cytokines and inflammatory response molecules were modulated in the head kidney of rOmpC-immunized L. rohita. While IgM, IL1β, and TLR-22 were significantly up-regulated at early time points (3 h-72 h), the others showed a transient augmentation at both early and later time points (SOD, lysozymes C and G, NKEF-B, C3, CXCa and TNF-α) in the rOmpC-immunized L. rohita in comparison to PBS-injected controls. These data suggest that the rOmpC-induced immune response is temporally regulated to confer immunity. In vivo challenge of the rOmpC-immunized fish with A. hydrophila showed significantly greater survival when compared to PBS-injected control fish. Thus, our results highlight the immunomodulatory role of rOmpC and demonstrate its protective efficacy in L. rohita, along with the use of anti-rOmpC antisera in detecting Aeromonas infections.

Toll-like receptors (TLRs) respond to tributyltin chloride (TBT-Cl) exposure in the river pufferfish (Takifugu obscurus): Evidences for its toxic injury function

Tributyltin chloride (TBT-Cl) residual in water body had become a noticeable ecological problem for aquatic ecosystems. Toll-like receptors (TLRs) are an ancient family of pattern recognition receptors that play key roles in detecting nonself antigens and immune system activation. In this study, we explored the effect of TBT-Cl exposure on four TLRs expression in river pufferfish, Takifugu obscurus. The four T. obscurus Toll-like receptors (To-TLRs) contained different types of domains such as leucine-rich repeats (LRRs), leucine-rich repeats, typical subfamily (LRR_TYP) and other special domains. The To-TLRs mRNA transcripts expressed in all tissues, also To-TLR2 was investigated with higher level in kidney, as well as To-TLR3 in kidney, while To-TLR18 in liver and To-TLR22 in intestine. After the acute and chronic exposure of TBT-Cl, To-TLR2 and To-TLR3 mRNA transcripts were significantly down-regulated in gill. However, To-TLR18 and To-TLR22 were significantly up-regulated in gill and liver. Moreover, the histology and immunohistochemistry (IHC) results showed the different injury degrees of TBT-Cl in liver and gill and implied the cytoplasm reorganization after TBT-Cl stress and the function of immunoregulation for To-TLRs to TBT-Cl exposure. All the results indicated that To-TLRs might involve in sensing and mediating innate immune responses caused by TBT-Cl for keeping detoxification homeostasis.

Comparative Tandem Mass Tag-Based Quantitative Proteomic Analysis of Tachaea chinensis Isopod During Parasitism

Parasitic isopods perforate and attach to the host integument via the mandibles and then feed on hemolymph and exudate from the wounds. Such isopods attack a variety of commercially important fish and crustacean hosts. Similar to other hematophagous parasites, isopods may also employ biomolecules that affect host blood conglutination and defense systems. In the present study, a tandem mass tag-based quantitative proteomic approach was used to identify differentially expressed proteins in Tachaea chinensis parasites of shrimp, by comparing parasitic (fed) and pre-parasitic (unfed) individuals. We identified 888 proteins from a total of 1,510 peptides, with a significant difference in 129 between the fed and unfed groups. Among these, 37 were upregulated and 92 were downregulated in unfed T. chinensis. This indicates that T. chinensis may require more energy before parasitism during its search for a host. In addition, as is the case for other blood-sucking parasites, it might secrete antihemostatic, anti-inflammatory, and immunomodulatory molecules to facilitate blood meal acquisition. To our knowledge, this study is the first to use a TMT-based proteomic approach to analyze the proteome of isopod parasites, and the results will facilitate our understanding of the molecular mechanisms of isopod parasitism on crustaceans.

Catching the complexity of salmon-louse interactions

The study of host-parasite relationships is an integral part of the immunology of aquatic species, where the complexity of both organisms has to be overlayed with the lifecycle stages of the parasite and immunological status of the host. A deep understanding of how the parasite survives in its host and how they display molecular mechanisms to face the immune system can be applied for novel parasite control strategies. This review highlights current knowledge about salmon and sea louse, two key aquatic animals for aquaculture research worldwide. With the aim to catch the complexity of the salmon-louse interactions, molecular information gleaned through genomic studies are presented. The host recognition system and the chemosensory receptors found in sea lice reveal complex molecular components, that in turn, can be disrupted through specific molecules such as non-coding RNAs.

Expression of infection-related immune response in European sea bass (Dicentrarchus labrax) during a natural outbreak from a unique dinoflagellate Amyloodinium ocellatum

In the Mediterranean area, amyloodiniosis represents a major hindrance for marine aquaculture, causing high mortalities in lagoon-type based rearing sites during warm seasons. Amyloodinium ocellatum (AO) is the most common and important dinoflagellate parasitizing fish, and is one of the few fish parasites that can infest several fish species living within its ecological range. In the present study, A. ocellatum was recorded and collected from infected European sea bass (Dicentrarchus labrax) during a summer 2017 outbreak in north east Italy. Histological observation of infected ESB gill samples emphasized the presence of round or pear-shaped trophonts anchored to the oro-pharingeal cavity. Molecular analysis for small subunit (SSU) rDNA of A. ocellatum from gill genomic DNA amplified consistently and yielded 248 bp specific amplicon of A. ocellatum, that was also confirmed using sequencing and NCBI Blast analysis. Histological sections of ESB gill samples were addressed to immunohistochemical procedure for the labelling of ESB igm, inos, tlr2, tlr4, pcna and cytokeratin. Infected gills resulted positive for igm, inos, pcna and cytokeratin but negative to tlr-2 and tlr-4. Furthermore, ESB immune related gene response (innate immunity, adaptive immunity, and stress) in the course of A. ocellatum infection using quantitative polymerase chain reaction (qpcr) for infected gills and head kidney was analysed. Among the twenty three immune related gene molecules tested, cc1, il-8, il-10, hep, cox-2, cla, cat, casp9, and igt were significantly expressed in diseased fish. Altogether, these data on parasite identification and expression of host immune-related genes will allow for a better understanding of immune response in European sea bass against A. ocellatum and could promote the development of effective control measures.

Effect of miconazole nitrate on immunological response and its preventive efficacy in Labeo rohita fingerlings against oomycetes Saprolegnia parasitica

This study evaluated the effect of sublethal doses of antifungal drug miconazole nitrate (MCZ) on immunological responses and its role as a prophylactic drug against S. parasitica in Labeo rohita fingerlings. Fish were fed with sublethal doses of MCZ, that is, T1-6.30 mgMCZ kgBW^-1 , T2-12.61 mgMCZ kgBW^-1 and T3-25.22 mgMCZ kgBW^-1 , and sampling was done at different time intervals for 240 hr. Immunological parameters viz. lysozyme activity, oxygen radical production and plasma antiprotease activity showed significant enhancement (p < 0.05) in fish fed with T2 and T3 doses. Expression of immune-relevant genes such as TLR-22 and β2-M showed significantly higher expression at 6 hr and 24 hr of sampling in both liver and head kidney. However, these genes showed a downregulation after 120 hr of sampling in both the tissues. Preventive efficacy study showed that single dose of MCZ provides protection against oomycetes up to the fourth day of infection. Significantly higher mortality was observed in control diet-fed fish as compared to fish fed with MCZ medicated diet. Thus, it can be concluded that the MCZ can act as a potent antifungal agent for preventing oomycetes infection as well as to enhance the immune response.

Modulation of immune response and protective efficacy of recombinant outer-membrane protein F (rOmpF) of Aeromonas hydrophila in Labeo rohita

The outer-membrane proteins (OMPs) of Aeromonas hydrophila, an imperative fish pathogen accountable for massive economic losses to aquaculture industry, are found to be immunogenic and considered as potential vaccine candidates. In spite of development in the formulation of vaccine candidates against Aeromonas infection, no commercial preparation has been done so far; in addition, the molecular mechanisms of immunoprotection induced by various vaccine formulations in Indian major carp, Labeo rohita, are little known. The present study was undertaken to evaluate the modulation of immunity and expression of immune-related genes post-rOmpF (recombinant outer-membrane protein of A. hydrophila, a novel vaccine candidate) immunization and protective efficacy after A. hydrophila challenge. The rOmpF-immunized fish showed a variable expression of the immune-related genes, viz. toll-like receptor 22 (TLR), complement component 3 (C3), chemokine (CXCa), tumor necrosis factor-α (TNFα), interleukin 1β (IL-1β), manganese superoxide dismutase (MnSOD) and natural killer enhancing factor (NKEF) in the head kidney tissues, when compared to the control group at different time intervals post-vaccination. A significant increase in serum hemolysin titer, ceruloplasmin level and myeloperoxidase activity was observed on day 140 post immunization. Also, bacterial agglutination titer and antiprotease activity were significantly increased on day 42 post immunization. No significant change was observed in lysozyme activity. Challenge studies with live A. hydrophila on day 140 post-immunization of L. rohita significantly increased the relative percentage survival (∼44%) in the vaccinated group. The results suggest that the rOmpF could be used as a potential vaccine candidate to combat A. hydrophila infection in fish.

Expression analysis of immune genes in goldfish (Carassius auratus) infected with the monogenean parasite Gyrodactylus kobayashii

Heavy infection with the ectoparasite Gyrodactylus kobayashii commonly leads to high mortality of ornamental goldfish Carassius auratus. To understand the underlying mechanisms of goldfish against infection of gyrodactylids, transcription responses of immune-related genes including IL-1β2, TNFα1, TNFα2, IFN-γ, TGFβ, MHC II β, TCRβ1 and complement factor C3 were studied by real-time quantitative PCR analysis. Significant increases of expression of inflammatory genes such as IL-1β2, TNFα1, TNFα2 and TGFβ were detected at days 7 and 14 post-infection (pi). No significant differences of G. kobayashii load were observed in response to primary infection and re-infection. In addition, the transcript levels of genes involved in adaptive immunity such as MHC II β and TCRβ1 remained unchanged. Curiously, fish moderately infected with gyrodactylid showed elevated expression IL-1β2, TNFα1 and TNFα2. In all the gyrodactylids-infected fish, expression of complement factor C3 was consistently inhibited. The results extend current knowledge to the understanding of gyrodactylid infection in fish and support the previous findings that innate immunity is indispensable for controlling parasite infection.

Transcriptional analysis of immune-relevant genes in the mucus of Labeo rohita, experimentally infected with Argulus siamensis

The knowledge of mucosa-associated molecular events that occur during infections is scarce despite the well-established importance of mucus in fish immunity. Using qRT-PCR, we analyzed the immune gene expression patterns in mucus of Labeo rohita experimentally infected with an ectoparasite Argulus siamensis. Mucus samples were collected at 0 h, 12 h, 24 h, 3 d, 7 d, 15 d, and 30 d post challenge of L. rohita with metanauplii of A. siamensis. All interleukins studied herein (IL 6, IL 15, and IL 1β) showed significant upregulation of expression levels in mucus of A. siamensis-infected fish compared to control samples. Further, the expression levels of molecules involved in pathogen recognition, toll like receptor 22, and pathogen presentation, β2 microglobulin, were found to be significantly upregulated in experimental samples until 7 d post challenge compared to control samples. The upregulated expression of lysozyme G at all time points post infection indicated the early activation of acute phase responses in mucus of infected L. rohita. Moreover, the expression levels of natural killer cell enhancing factor B were found to be higher in infected fish than they were in the control fish. The early upregulation of the immune genes observed herein reinforces the role of mucus as the first line of defense against pathogenic assault; furthermore, it expands our understanding of mucosal-immune responses to A. siamensis infection, which can aid development of immunological interventions.

Physiological and proteomic responses to corticosteroid treatments in Eurasian perch, Perca fluviatilis: Investigation of immune-related parameters

The comparative effects of cortisol and 11-deoxycorticosterone (DOC), two major corticosteroids in fish, have yet received little attention in teleosts. We evaluated the proteomic and immune responses of Eurasian perch to chronic corticosteroid treatments. We implanted immature perch with cortisol (80mg/kg) or DOC (4mg/kg) and measured the proportions of blood leucocytes, immune indices in the plasma, spleen and liver (complement and lysozyme activity, total immunoglobulin and immune gene expression in the tissues) and differential proteome expression (corticosteroid versus control) in the liver and the spleen on days 2, 4 and 14 post-treatment. Implantation of cortisol decreased the ratio of blood leucocytes and depressed Ig levels in both organs while DOC modulated the proportion of leucocyte sub-populations (increase in lymphocytes and decrease in granulocytes). In contrast, the innate humoral immunity was not strongly influenced by any of corticosteroid implants. The only immune parameter that was significantly affected was lysozyme, after DOC treatment. A number of proteins were differentially regulated by these hormones and some were identified in the liver (21 for cortisol and 8 for DOC) and in the spleen (10 for cortisol and 10 for DOC). None of the proteins was directly linked to immunity, except the natural killer enhancing factor, which was repressed by cortisol in the spleen. Our results also confirm that the proteins involved in energetic and glucose metabolism are affected by corticosteroids. Furthermore, these corticosteroids differently regulate immune status in Eurasian perch and they primarily impact leucocytes, as opposed to innate immune function.

Hook, Line and Infection: A Guide to Culturing Parasites, Establishing Infections and Assessing Immune Responses in the Three-Spined Stickleback

The three-spined stickleback (Gasterosteus aculeatus) is a model organism with an extremely well-characterized ecology, evolutionary history, behavioural repertoire and parasitology that is coupled with published genomic data. These small temperate zone fish therefore provide an ideal experimental system to study common diseases of coldwater fish, including those of aquacultural importance. However, detailed information on the culture of stickleback parasites, the establishment and maintenance of infections and the quantification of host responses is scattered between primary and grey literature resources, some of which is not readily accessible. Our aim is to lay out a framework of techniques based on our experience to inform new and established laboratories about culture techniques and recent advances in the field. Here, essential knowledge on the biology, capture and laboratory maintenance of sticklebacks, and their commonly studied parasites is drawn together, highlighting recent advances in our understanding of the associated immune responses. In compiling this guide on the maintenance of sticklebacks and a range of common, taxonomically diverse parasites in the laboratory, we aim to engage a broader interdisciplinary community to consider this highly tractable model when addressing pressing questions in evolution, infection and aquaculture.

Comparative immunity of Salmo salar and Oncorhynchus kisutch during infestation with the sea louse Caligus rogercresseyi: An enrichment transcriptome analysis

Caligus rogercresseyi, an ectoparasite affecting the Chilean salmon industry, can cause immunosuppression and physiological stress in farmed fish. Interestingly, coho salmon (Oncorhynchus kisutch) are notably resistant to infestation, whereas Atlantic salmon (Salmo salar) are phenotypically more susceptible to sea lice. However, comparative studies on immune responses to C. rogercresseyi have not been conducted. In this study, Illumina sequencing was conducted to evaluate head kidney and skin samples taken 7 and 14 days post-infestation, yielding a total of 1492 and 1522 contigs annotated to immune-related genes for Atlantic and coho salmon, respectively. Both species evidenced an upregulation of inflammatory genes. Atlantic salmon had highly upregulated TLR22 and MHCII at 14 days post-infestation, while coho salmon had highly upregulated stat5 and il1r transcripts. Fourteen transcripts related to T_H1, T_H2, TLR, and macrophage responses were corroborated via RT-qPCR. Statistical analyses indicated an upregulation of mmp13, cox2, il10, ccr3, tlr22a2, and tlr21 in Atlantic salmon and of ifnγ, cd83, T-bet, tlr13, and tlr19 in coho salmon. These results suggest strong differences between the Atlantic and coho salmon immune responses, where coho salmon, the more resistant species, presented a primary T_H1 response. Additionally, putative roles of TLRs in salmonids against sea lice were evidenced. This study is the first comparative transcriptome analysis that reveals species-specific immune responses in salmons infected with C. rogercresseyi.

Immunotoxicological effects of cadmium on Labeo rohita, with emphasis on the expression of HSP genes

The present study evaluated the effects of exposure (28 days) to a sub-lethal concentration of cadmium (Cd) (0.65 mg CdCl2 L(-1)) on the immune responses and expression of immune-related and heat shock protein (HSP) genes in Labeo rohita, an important aquacultured fish species. Among the immune parameters studied, significantly lower lysozyme activity was observed in fish 28 days post-exposure (dpe) to Cd as compared to control fish. Alternative complement pathway activity was slightly higher in the Cd-exposed group at 2 dpe than in controls, and this activity declined gradually thereafter. The phagocytic activity and serum immunoglobulin M (IgM) levels were insignificantly lower in the Cd-exposed group at all assessed time points than in controls. Among serum enzymatic activities, peroxidase activity was always higher in the Cd-exposed group than in controls, but the increase was insignificant at all assessed time points. Additionally, serum glutamic-pyruvic transaminase and alkaline phosphatase activities were significantly higher in the Cd-exposed group at 14 and 28 dpe. Immune and HSP gene expression patterns were observed in kidney and liver tissues, respectively, by RT-PCR, and HSPs were further analysed by immunoblotting. Cd had an immunosuppressive effect, leading to down-regulation of TNF-α, IL-1β, IL-10, and IFN-γ. However, Cd exposure led to the up-regulation of HSP47, HSP60, HSP70, HSP78, and HSP90, indicating Cd-induced cellular stress. Taken together, the results of this study demonstrate the immunotoxic effect of Cd. Cd exposure makes Labeo rohita immunocompromised, and this could subsequently increase the disease susceptibility of Labeo rohita.

Four pro-inflammatory cytokines of rohu (Labeo rohita) during early developmental stages, their tissue distribution and expression by leucocytes upon in-vitro stimulation

Cytokines are important components of both adaptive and innate immunity, and are required to initiate and regulate immune responses following infection. The ontogeny and tissue specific distribution of four pro-inflammatory cytokines, interleukin-6 (IL-6), tumor necrosis factor α (TNF-α), IL-8 and IL-1β in rohu (Labeo rohita), and their responses by leucocytes from anterior-kidney/head-kidney (HKLs), spleen (SPLs) and peripheral blood (PBLs) following stimulation with concanavalin A (ConA), ConA with phorbol 12-myristate 13-acetate (ConA/PMA) and formalin-killed Aeromonas hydrophila cells (FAH) were studied. In ontogeny study, mRNA levels of IL-6 and IL-1β were evident in unfertilized egg stages of L. rohita whereas IL-8 and TNF-α transcripts were found from 1 to 3 h post-fertilization (hpf) onwards till day 15 post-fertilization, respectively. Basal level of all four cytokines was observed in all twelve tissues (eye, brain, heart, gill, anterior kidney, posterior kidney, spleen, liver, skin, muscle, hindgut and foregut) of L. rohita juveniles. Expression levels of IL-6 and IL-8 were found to be the highest in liver and heart tissues, respectively, while TNF-α transcripts were high in anterior kidney and liver tissues. Transcripts of IL-1β showed high expression in muscle, heart and spleen. Upon in vitro stimulation of leucocytes, there was variable up-regulation of all the four cytokines following different treatments throughout the experimental time period. Induction of cytokines was more pronounced in PBLs stimulated with FAH compared to other stimuli. However, an up-regulated IL-8 expression was evident in all the leucocytes following stimulation with FAH thus indicating IL-8 could be used as an indicator or indirect marker to monitor vaccine status or health status of L. rohita during bacterial infection.

Transcriptional changes in three immunoglobulin isotypes of rohu, Labeo rohita in response to Argulus siamensis infection

Immunoglobulin heavy chains of three isotypes viz., IgM, IgD and IgT/IgZ are described in teleosts. In this study, a challenge experiment with an ectoparasite Argulus siamensis was conducted to evaluate the changes in adaptive immune response by quantitation of expression of Ig heavy chains in skin, head kidney and mucus of infected rohu, Labeo rohita. Rohu were challenged with 100 metanauplii of A. siamensis/fish. Head kidney, skin and mucus samples were collected at 0 h, 12 h, 24 h, 3 d, 7 d, 15 d and 30 d by sacrificing four fish each from infected and control groups at each time point. The expression of IgM, IgD and IgZ in these tissues were measured by reverse transcription real time quantitative PCR. IgM level was found to reach its peak significantly 30 d post-infection in head kidney tissue, while IgM transcripts were below detectable range in skin and mucus at all time points. IgZ and IgD levels were significantly up-regulated post-infection in all the three tissue samples. Early up-regulation of IgD was observed in skin and mucus, compared to head kidney. This study showed that parasitic invasion can trigger varied expressions of immunoglobulin types to provide systemic as well as local protection in the host. In particular, the appearance of high level of expression of IgZ and IgD in skin and mucus will pave the way for vaccine development against A. siamensis which feeds on those tissues.

Molecular cloning and comparative responses of Toll-like receptor 22 following ligands stimulation and parasitic infection in yellowtail (Seriola lalandi)

TLR22 is exclusively present in teleosts and amphibians and is expected to play the distinctive role in innate immunity. In this study, we cloned the full-length cDNA sequence of yellowtail (Seriola lalandi) TLR22 (SlTLR22). The complete cDNA sequence of SlTLR22 was 4208 bp and encodes a polypeptide of 961 amino acids. Analysis of the deduced amino acid sequence indicated that SlTLR22 has typical structural features of proteins belonging to the TLR family. These included 17 LRR domains (residues 91-633) and one C-terminal LRR domain (LRR-CT, residues 693-744) in the extracellular region, and a TIR domain (residues 800-943) in the cytoplasmic region. Comparison with homologous proteins showed that the deduced SlTLR22 has the highest sequence identity to turbot TLR22 (76%). Quantitative real-time PCR (qPCR) analysis demonstrated the constitutive expression of SlTLR22 mRNA in all examined tissues with higher levels in the head kidney, intestine, skin and spleen. Further, SlTLR22 expression was significantly up-regulated following TLR ligands injection with lipopolysaccharide (LPS), CpG ODN2006 and polyinosinic: polycytidylic acid (poly I:C) in spleen and liver. Amyloodinium ocellatum infection also induced a high expression of SlTLR22 in spleen, intestine, muscle, skin and gill, with maximum increases ranging from 1000 to 100 fold upon different ligands and organs. Finally, histological examination in gill tissue confirmed infection by the parasite and histopathological lesion was observed also in spleen and skin. These findings suggest a possible role of SlTLR22 in the immune responses to the infections of a broad range of pathogens that include DNA and RNA viruses and parasites.

Immunomodulatory effect of arsenic on cytokine and HSP gene expression in Labeo rohita fingerlings

Immune system is fundamental for survival of an organism against invading pathogens and other harmful agents. Cytokines, the signaling proteins that are produced transiently after cell activation and exert pleiotropic effects on cells of the immune system, are important mediators of cell mediated immune response. When expressed in a dysregulated fashion cytokines can underlie either immunodeficient or immunopathologic states. Heat shock proteins (stress proteins, HSPs) are also key proteins, which play important role in immunomodulation, apoptosis and influence the immune responses. Arsenic is a major toxic environmental contaminant and a human carcinogen. Prolonged drinking of arsenic-contaminated water leads to chronic arsenic toxicity (arsenicosis). Arsenic is also immunotoxic and renders the host immunocompromised. Arsenic exposure has been reported to result in growth retardation, gross pathology including skin and eye lesions, ulcerations, cataract development etc. in different fish species. The present study was undertaken to investigate the effect of arsenic exposure on the expression of immune genes IFN-γ, IL-4, IL-10, IL-12, complement C3a and HSP genes HSP47, HSP60, HSP70, HSC71, HSP78, and HSP90 in Labeo rohita, an important aquacultured species, as such information is not available on this major carp. Cytokine and HSP gene expression analyses were carried out in kidney and liver tissues, respectively, in arsenic-exposed fishes by RT-PCR and HSPs were analyzed by immunoblotting. It was observed that arsenic has a generalized immune-suppressive effect leading to down regulation of both Th1 and Th2 cytokines; besides, it led to up regulation of the HSP genes indicating arsenic-induced cellular stress. Thus arsenic exposure makes L. rohita immunocompromised and could increase its susceptibility to pathogen attacks.

First evidence of comparative responses of Toll-like receptor 22 (TLR22) to relatively resistant and susceptible Indian farmed carps to Argulus siamensis infection

Toll-like receptor 22 (TLR22) is present in teleost but not in mammals. Among Indian farmed carps, Catla catla is relatively more resistant than Labeo rohita to Argulus siamensis lice infection. TLR22 is believed to be associated with innate immunity against ectoparasite infection. To investigate the TLR22 mediated immunity against argulosis, we have cloned and characterized TLR22 genes of L. rohita (rTLR22) and C. catla (cTLR22). The full-length cDNAs of rTLR22 and cTLR22 contained an open reading frame of 2838 and 2841 nucleotides, respectively; bearing the typical structural features. Phylogenetically rTLR22/cTLR22 was most closely related to Cyprinus carpio (common carp) counterpart, having highest sequence identity of 86.0%. The TIR domain remained highly conserved with 90% identity within freshwater fishes. The sequence information of cDNA and genomic DNA together revealed that the rTLR22/cTLR22 genes are encoded by uninterrupted exons. The co-habitation challenge study with A. siamensis infection confirmed that C. catla is comparatively more resistant than L. rohita. Further, comparative mRNA expression profile in immune relevant tissues also suggested about the participatory role of TLR22 during lice infection. However, TLR22 might not solely be involved in conferring relative resistance among carp species against argulosis.

Stress mitigating and growth enhancing effect of dietary tryptophan in rohu (Labeo rohita, Hamilton, 1822) fingerlings

An experiment was conducted to study the stress mitigation and growth enhancing role of dietary L-tryptophan (TRP) under thermal stress in rohu, Labeo rohita fingerlings for 45 days. Seven hundred and twenty fishes were distributed in three major groups that are ambient temperature (26 °C), 34 and 38 °C in triplicate following a complete randomized design. Acclimation of fishes to 34 and 38 °C over average ambient temperatures were carried out at 1 °C/day. Each group was fed with a diet supplemented with 0, 0.36, 0.72 or 1.42 % L-TRP. Results showed that blood glucose and serum cortisol level were found to be significantly higher (p < 0.05) in the higher temperature groups than the ambient temperature group. Similarly, aminotransferase, lactate dehydrogenase, malate dehydrogenase, CAT, superoxide dismutase activities were found to be significantly higher (p < 0.05) in the control groups (0 % L-TRP) and decreasing activities of these enzymes were observed with the increasing level of dietary L-TRP. In different temperature groups, L-TRP-supplemented groups were found to have higher (p < 0.05) growth, RGR and PER. The results obtained in the present study indicate that dietary L-TRP mitigates thermal stress and enhances growth. From the present study, we can conclude that dietary supplementation of L-TRP at the 0.72 % level in the diet is found to be optimum to reduce thermal stress even up to 38 °C in rohu, L. rohita. The baseline data obtained here could be useful for the farmers to formulate feeds to culture the fish in different agro-climatic zones.

Toll-like receptor 22 in Labeo rohita: molecular cloning, characterization, 3D modeling, and expression analysis following ligands stimulation and bacterial infection

Toll-like receptors (TLRs) are a class of innate immune receptors that sense pathogens or their molecular signatures and activate signaling cascades to induce a quick and non-specific immune response in the host. Among various types of TLRs, TLR22 is exclusively present in teleosts and amphibians and is expected to play the distinctive role in innate immunity. This report describes molecular cloning, three-dimensional (3D) modeling, and expression analysis of TLR22 in rohu (Labeo rohita), the most commercially important freshwater fish species in the Indian subcontinent. The open reading frame (ORF) of rohu TLR22 (LrTLR22) comprised of 2,838 nucleotides (nt), encoding 946 amino acid (aa) residues with the molecular mass of ∼ 107.6 kDa. The secondary structure of deduced LrTLR22 exhibited the presence of signal peptide (1-22 aa), 18 leucine-rich repeat (LRR) regions (79-736 aa), and TIR domain (792-935 aa). The 3D model of LrTLR22-LRR regions together elucidated the horse-shoe-shaped structure having parallel β-strands at the concave surface and few α-helices at the convex surface. The TIR domain structure revealed alternate presence of five α-helices and β-sheets. Phylogenetically, LrTLR22 was closely related to common carp and exhibited significant similarity (92.2 %) and identity (86.1 %) in their amino acids. In rohu, TLR22 was constitutively expressed in all embryonic developmental stages, and tissue-specific analysis illustrated its expression in all examined tissues, highest was in liver and lowest in brain. In vivo modulation of TLR22 gene expression was analyzed by quantitative real-time PCR (qRT-PCR) assay following stimulation with lipopolysaccharide (LPS), synthetic double stranded RNA (polyinosinic-polycytidylic acid), and bacterial (Aeromonas hydrophila) RNA. Among these ligands, bacterial RNA most significantly (p < 0.05) induced TLR22 gene expression in most of the tested tissues. In A. hydrophila infection, induction of TLR22 gene expression was also observed in majority of the tested tissues. Together, these data suggested that in addition to sensing other microbial signatures, TLR22 can recognize bacterial RNA and may play the important role in augmenting innate immunity in fish.

Modulation of cellular innate immunity by Lepeophtheirus salmonis secretory products

Lepeophtheirus salmonis produces pharmacologically active substances that have been shown to modify genetic expression of inflammatory mediators in SHK-1 cells and head kidney macrophages of salmon. Differences in genetic expression among genera of Oncorhynchus and Salmo reflect different susceptibilities to L. salmonis. This study was conducted to determine if the presence of L. salmonis secretory products (SEPs)(1) alters the cellular innate immune response (specifically macrophage function) among several salmonids. Phagocytic assays were performed using SHK-1 cells and macrophages isolated from pink (Oncorhynchus gorbuscha), chum (Oncorhynchus keta) and Atlantic (Salmo salar) salmon following incubation with SEPs and Aeromonas salmonicida. Respiratory burst assays were analyzed using pink, chum and Atlantic salmon macrophages after exposure to SEPs. For SHK-1 cells, incubation with SEPS led to dose-dependent increases in phagocytosis. Following incubation with SEPs, chum salmon macrophages had the highest phagocytic index (55.1%) followed by Atlantic (26.4%) and pink (15.8%) salmon. In contrast, respiratory burst response was greatest in pink salmon and minimal in the other two species. Our results suggest that the cellular innate immune response of salmon is modified in the presence of L. salmonis secretions and differences observed among species provide insight into species-specific consequences of sea lice infection.

cDNA cloning and expression characterization of serum transferrin gene from oriental weatherfish Misgurnus anguillicaudatus

In this study, the cDNA coding serum transferrin (stf) of Misgurnus anguillicaudatus (mastf) was cloned. mastf cDNA is composed of 2326 bp with a 2007 bp open reading frame encoding 668 amino acids. The deduced Mastf protein consists of a signal peptide, two lobes (N and C-lobes) and signature motifs of transferrin (Tf) family. The results of tissue distribution indicated that mastf mRNA was predominantly expressed in the liver. The results indicate that the mastf expression increased significantly in liver, blood, spleen and head kidney after the challenge with Aeromonas sobria, acting as a positive acute protein, suggesting that mastf is related to the immune response. The cloning and expression analysis of mastf further demonstrates the evolutionary conservation of Stf and immune function in vertebrates.

Expression of immune-related genes in goldfish gills induced by Dactylogyrus intermedius infections

Dactylogyrus intermedius, an oviparous monogenean parasite, is regarded as a devastating pathogen in freshwater aquaculture and ornamental fish trade, and accounts for significant economic losses worldwide. The study was undertaken to determine the differential expression of immune-related genes TNFα1, TNFα2, IL-1β2, TGFβ, iNOSa and iNOSb in goldfish gills during D. intermedius infection by real-time quantitative PCR. The results show that the expression of the pro-inflammatory cytokines (IL-1β2, TNFα1 and TNFα2) and the anti-inflammatory cytokine (TGFβ) were up-regulated at day 7 p.i. (post infection). The mRNA levels of these cytokines returned to normal levels or were down-regulated at day 21 p.i. In the cases of iNOSa and iNOSb, a significant up-regulation in iNOSa transcription levels were seen at day 14 p.i. while the expression of iNOSb gene showed a distinct up-regulation at day 7 p.i. Additionally, this study was conducted to investigate the expression of immune-related genes in different degrees of goldfish experimentally infected with the monogenean D. intermedius. The results indicated that D. intermedius infection might regulate the fish immunity by showing differential expression levels of immune-related gene. The study confirms goldfish gill acts as an important source of inflammatory molecules, as well as an active modulator of local inflammation after initially infected with D. intermedius. Moreover, the results obtained in this study could be useful towards understanding the susceptibility of goldfish to D. intermedius and mechanisms involved in protection of goldfish to ectoparasitic infections.

Orange-spotted grouper (Epinephelus coioides) toll-like receptor 22: molecular characterization, expression pattern and pertinent signaling pathways

The toll-like receptors (TLRs) are an important gene family in host innate immunologic surveillance. The TLR22 gene is an essential member of the TLRs that is only found in aquatic animals and has been detected in some bony fish. Here, a TLR22 homolog, EcTLR22, was characterized in the orange-spotted grouper (Epinephelus coioides) via homology cloning. The 3321 bp full-length cDNA sequence of EcTLR22 was obtained, which included an open reading frame of 2880 bp encoding a putative peptide of 960 amino acids containing three highly typical domains with the characteristics of TLR family members. The deduced amino acid sequence of EcTLR22 showed a relatively high similarity to flounder TLR22. Phylogenetic analysis showed that the orange-spotted grouper TLR22 sequence was clustered with those of Perciforme, such as flounder and croaker. Real-time quantitative PCR analysis revealed broad expression of EcTLR22, with relatively high expression detected in the head kidney, trunk kidney, spleen, peripheral blood leukocytes (PBLs) and heart of orange-spotted grouper. After injection with Vibrio alginolyticus, there was significant up-regulation of the expression of EcTLR22 in the spleen. In evaluating unstimulated/stimulated head kidney leukocytes and spleen leukocytes, a significant increase in EcTLR22 mRNA expression was detected, which implied a sensitive immune response. Furthermore, four important molecules for signal transduction, MyD88, TRIF, TNF-α and IRF3, were chosen to analyze the role of the EcTLR22 signaling pathway in anti-pathogen responses. Upon LPS or Poly I:C challenge, expression of the four genes was induced, with an increasing tendency detected in head kidney leukocytes, suggesting that the four genes might work with EcTLR22 in host defense against pathogenic microbes.

Egg laying strategies and effect of temperature on egg development of Argulus siamensis

Argulus siamensis is the most damaging fish parasite prevalent in the freshwater aquaculture systems of India. In an attempt to further understand the behavior of this economically important parasite, the means of biological transmission, egg laying strategies and effect of temperature on development of eggs was studied. A. siamensis showed opportunistic egg laying behavior where in it used both living and non-living substrata for egg laying. It was marked that the parasites used the shells of freshwater snails of the family Viviparidae, the runners of the water weeds of genus Nymphoides and dead fish in the culture ponds for laying of eggs. This study confirmed that the maximum eggs were laid by the parasite in the habitat usage zone of the host fish. The optimum temperature for development of the eggs of A. siamensis into the infective naupliar stage and hatching was found to be 28 °C. These new insights into the behavior of A. siamensis would be helpful to devise biological control methods against the parasite.

Efficacy of two avermectins, doramectin and ivermectin against Argulus siamensis infestation in Indian major carp, Labeo rohita

The efficacy of two avermectins, doramectin and ivermectin via oral and parenteral routes and their prophylactic effects against Argulus siamensis infestation in Indian major carp, Labeo rohita was studied. Doramectin and ivermectin were fed once to L. rohita sub-adults naturally infested with A. siamensis parasites at graded levels of 1000, 750 and 500 μg/kg body weight and 500, 300 and 200 μg/kg body weight, respectively. The mean time of clearance of parasites was 24 ± 0.149 h for 1000 and 24 ± 0.210 h for 750 μg of doramectin/kg body weight fish, however, the dose of 1,000 μg resulted in adverse reactions and mortality in fish. A single dose of 500μg/kg body weight of ivermectin also cleared the infestation in 24 ± 0.258 h. In second experiment, L. rohita naturally infested with A. siamensis were administered with doramectin and ivermectin intramuscularly as single dose of 200, 150 and 100 μg/kg body weight. Both doramectin and ivermectin at 200 μg/kg body weight cleared the infestation in 4 ± 0.149 and 4 ± 0.258 h respectively, however, those resulted in adverse reactions viz., black pigmentation, lethargy and poor appetite in fish. The mean time of clearance of parasites from fish was 6 ± 0.210 and 12 ± 0.314 h for doramectin and ivermectin, respectively, when given at a lower dose of 150 μg/kg body weight. The prophylactic effects of both drugs were also evaluated by challenging naïve rohu with metanaupliar larvae of A. siamensis after feeding the fish single dose of the doramectin and ivermectin at 750 and 500 μg/kg body weight, respectively. The effects of both the drugs were found to last for 17-18 days. The effects of bath treatment with doramectin and ivermectin at different concentrations on adult A. siamensis and metanaupliar larvae of A. siamensis were also evaluated. The results suggested that ivermectin could act more rapidly compared to doramectin. However, detailed studies on the toxicity and pharmacokinetics of doramectin and ivermectin upon their administration to aquatic organisms and the environmental impacts of their usage are required to be undertaken before finally recommending the safe use of these drugs for control of parasitic infections.

Freshwater abiotic components' impact on the viability of fish lice, Argulus sp., in Guangdong province, China

Parasite intensity dynamics can be strongly affected by ecosystem abiotic components. We conducted this study to investigate how the intensity of Argulus sp. is influenced by physicochemical factors in three water bodies - river, fish farm, and reservoir - and to find the occurrence of Argulus sp. under different conditions. Argulus sp. specimens were collected using different methods - gill-netting 30 × 1.5 m, 40 mm mesh monofilament net and set from a small boat, beach seining and plankton net - from July 2010 until Jun 2011 at Guangdong province, China. Main water parameters taken for the assessment consisting of temperature, pH, DO, biochemical oxygen demand of 5 days (BOD5), chemical oxygen demand (COD), NH (4) (+) , total nitrogen (TN) and total phosphorus (TP). The results show that the ratio of female to male Argulus sp. during the studied period was 2.3:1. The presence and intensity of Argulus sp. were temperature-dependent and variable; pH values were lower than standers with high intensity of Argulus sp. Argulus sp. has the ability to live in low dissolved oxygen (DO) concentration. Relatively high concentrations of BOD5, COD, NH (4) (+) , TN and TP were detected with related variable intensity of Argulus sp., which is supposed to be a freshwater fish ectoparasite found in polluted ecosystems. It is concluded that the fish ectoparasite Argulus sp. have a strong potency of genetic adaptation impacted by environmental factors. However, this needs further study in order to gain insight into the question of the likelihood of adaptation to abiotic factors' variation.

Identification, mRNA expression and genomic structure of TLR22 and its association with GCRV susceptibility/resistance in grass carp (Ctenopharyngodon idella)

Toll-like receptor 22 (TLR22) plays a crucial role in response to virus infection by recognizing double stranded RNA (dsRNA) in aquatic animals. In the present study, a TLR22 homologue gene was identified and characterized from grass carp (Ctenopharyngodon idella) (CiTLR22). CiTLR22 genomic sequence comprises 4754 base pairs (bp), containing one intron. The cDNA sequence consists of 3831bp, encoding a protein of 954 amino acid residues. CiTLR22 was constitutively expressed in all 15 investigated tissues, highly in gill and lowly in liver and spleen. The expression profile of CiTLR22 in spleen was rapidly and significantly up-regulated at 6h (456.13-fold, P<0.05), then rapidly recovered to normal level at 12h (P>0.05) post-injection of grass carp reovirus (GCRV). The expression levels of CiTLR22 were rapidly elevated post-poly(I:C) stimulation in dose- and time-dependent manners in CIK (C. idella kidney) cell line. After GCRV infection, CiTLR22 transcripts were inhibited at the early stage, then were up-regulated and reached a peak at 24h post-infection, latterly down-regulated in CIK cell culture. In the whole genomic sequence, six single nucleotide polymorphisms (SNPs) were detected. Five of them were sited in the coding region and all synonymous, and another located in the 5' untranslated region (UTR). The following SNP analysis revealed that 2406 C/T was just a mutation. Only 417 G/T was significantly associated with the resistance of grass carp to GCRV both in genotype (P=0.013) and allele (P=0.015). -8 A/T and 2574 C/T, 863 C/T and 1923 G/T, 863 C/T and 2574 C/T were pairwise linkage disequilibrium. None of the haplotype was associated with the resistance of grass carp to GCRV. The results indicate that CiTLR22 plays an important role in the responses to dsRNA and GCRV, and is partially inhibited by GCRV in vitro. The potential molecular marker lays foundation for the selective breeding of the GCRV-resistant grass carp.