Quantitative shotgun proteomics distinguishes wound-healing biomarker signatures in common carp skin mucus in response to Ichthyophthirius multifiliis

Catechol compounds as dual-targeting agents for fish protection against Ichthyophthirius multifiliis infections

Aquaculture is one of the fastest growing sectors in global food production, recognized as a significant contributor to poverty alleviation, food security, and income generation. However, the frequent occurrence of diseases caused by pathogen infections result in reduced yields and economic losses, posing a substantial constraint to the sustainable development of aquaculture. Here, our study identified that four catechol compounds, quercetin, luteolin, caffeic acid, and chlorogenic acid, exhibited potent antiparasitic effects against Ichthyophthirius multifiliis in both, in vitro and in vivo. The parasite is recognized as one of the most pathogenic to fish worldwide. Using a combination of in silico methods, the dipeptidyl peptidase (DPP) was identified as a critical target for catechol compounds. The two hydroxyl radicals of the catechol group were essential for its binding to and interacting with the DPP protein. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated that catechol compounds disrupt pathways associated with the metabolism and growth of I. multifiliis, thereby exerting antiparasitic effects. Furthermore, these compounds attenuated the expression of proinflammatory cytokines in vivo in fish and promoted macrophage polarization toward M2 phenotype by inhibiting the STAT1 signaling pathway. The dual activity of catechol compounds, acting as both direct antiparasitic and anti-inflammatory agents in fish, offers a promising therapeutic approach for combating I. multifiliis infections in aquaculture.

Bactericidal role of epidermal mucus of freshwater fish treated with Aeromonas hydrophila

This study explored the bactericidal role of the epidermal mucus (EM) of five freshwater Cyprinid fish species namely Ctenopharyngodon idella, Labeo rohita, Catla catla, Hypophthalmichthys molitrix, and Cirrhinus mrigala after treatment with Aeromonas hydrophila. Extracts of EM (crude and acidic) of each species showed bactericidal activity against various Gram -ve (Pseudomonas aeruginosa, Escherichia coli, Aeromonas hydrophila, Edwardsiella tarda, Salmonella enterica, Klebsiella pneumonia, Serratia marcescens, and Enterobacter cloacae) and Gram +ve (Bacillus wiedmannii and Staphylococcus aureus) bacteria compared with standard antibiotics (Fosfomycin). The zone of inhibition (ZOI) was measured in millimetres against antibiotics (Fosfomycin). Variations in bactericidal activity of EM were observed against bacteria from the same and different fish species. The acidic extract was more effective than the crude extract and showed significantly higher ZOI values against various bacteria and Fosfomycin antibiotics. This result shows that fish EM may perform an important role in fish defence against bacteria. Therefore, this study may hint towards the substitution of synthetic antibiotics with fish EM that may be used as a novel 'bactericidal' in aquaculture as well as in humans against bacterial infections.

Influences of chronic copper exposure on intestinal histology, antioxidative and immune status, and transcriptomic response in freshwater grouper (Acrossocheilus fasciatus)

Copper (Cu) contamination is commonly found in both natural water environments and fish farms, and it can cause severe damage to different fish organs, but Cu-induced intestinal damage has been rarely studied. This study subjected three groups of freshwater grouper (Acrossocheilus fasciatus) (initial weight: 1.56 ± 0.10 g) to 0 mg/L, 0.01 mg/L, and 0.04 mg/L Cu2+ for 30 days, named Con, Cu0.01, and Cu0.04 groups, respectively. The histological observation indicated that the Cu0.04 group caused a significant decrease in villus length, lamina propria width, and muscular thickness compared to the Con group (P < 0.05). Additionally, the Cu0.04 group significantly increased intestinal superoxide dismutase (SOD), glutathione peroxidase (GPx), lysozyme (LZM) activities, as well as malondialdehyde (MDA) content than the Con group (P < 0.05). Meanwhile, the Cu0.01 and Cu0.04 groups showed significantly increased immunoglobulin M (IgM), complement 3 (C3), and glutathione (GSH) contents than the Con group (P < 0.05). Transcriptomic analysis revealed a total of 101 differentially expressed genes (DEGs), including 47 up-regulated and 54 down-regulated DEGs, were identified between the Cu0.04 and Con groups. Notably, the DEGs were mainly related to intestinal structure construction, immune functions, apoptosis, and resistance to DNA damage and pathogen infection. The findings suggest that chronic Cu exposure caused intestinal histological alterations, activated the antioxidative and immune systems, and induced systematic adaptation to cope with the physical barrier injury, DNA damage, and potential pathogen growth.

Focal adhesion signaling pathway involved in skin immune response of tongue sole Cynoglossus semilaevis to Vibrio vulnificus infection

Focal adhesion (FA) plays a key role in cell adhesion, migration and antibacterial immune, but it remained unclear in fish. In this study, half-smooth tongue sole Cynoglossus semilaevis were infected with Vibrio vulnificus, and then immune-related protein in the skin, especially for FA signaling pathway were screened and identified by iTRAQ analysis. Results showed that the differentially expressed proteins (DEPs) in skin immune response (eg., ITGA6, FN, COCH, AMBP, COL6A1, COL6A3, COL6A6, LAMB1, LAMC1, FLMNA) were firstly found in FA signaling pathway. Furthermore, the validation analysis of FA-related genes were basically consistent with the iTRAQ data at 36 hpi (r = 0.678, p < 0.01), and their spatio-temporal expressions were confirmed by qPCR analysis. The molecular characterization of vinculin of C. semilaevis was described. This study will provide a new perspective for understanding the molecular mechanism of FA signaling pathway in the skin immune response in marine fish.

Silencing of heat shock protein 90 (hsp90): Effect on development and infectivity of Ichthyophthirius multifiliis

BACKGROUND

Recently, an increasing number of ichthyophthiriasis outbreaks has been reported, leading to high economic losses in fisheries and aquaculture. Although several strategies, including chemotherapeutics and immunoprophylaxis, have been implemented to control the parasite, no effective method is available. Hence, it is crucial to discover novel drug targets and vaccine candidates against Ichthyophthirius multifiliis. For this reason, understanding the parasite stage biology, host-pathogen interactions, molecular factors, regulation of major aspects during the invasion, and signaling pathways of the parasite can promote further prospects for disease management. Unfortunately, functional studies have been hampered in this ciliate due to the lack of robust methods for efficient nucleic acid delivery and genetic manipulation. In the current study, we used antisense technology to investigate the effects of targeted gene knockdown on the development and infectivity of I. multifiliis. Antisense oligonucleotides (ASOs) and their gold nanoconjugates were used to silence the heat shock protein 90 (hsp90) of I. multifiliis. Parasite stages were monitored for motility and development. In addition, the ability of the treated parasites to infect fish and cause disease was evaluated.

RESULTS

We demonstrated that ASOs were rapidly internalized by I. multifiliis and distributed diffusely throughout the cytosol. Knocking down of I. multifiliis hsp90 dramatically limited the growth and development of the parasite. In vivo exposure of common carp (Cyprinus carpio) showed reduced infectivity of ASO-treated theronts compared with the control group. No mortalities were recorded in the fish groups exposed to theronts pre-treated with ASOs compared with the 100% mortality observed in the non-treated control fish.

CONCLUSION

This study presents a gene regulation approach for investigating gene function in I. multifiliis in vitro. In addition, we provide genetic evidence for the crucial role of hsp90 in the growth and development of the parasite, suggesting hsp90 as a novel therapeutic target for successful disease management. Further, this study introduces a useful tool and provides a significant contribution to the assessing and understanding of gene function in I. multifiliis.

Investigating the effects of glyphosate on the bumblebee proteome and microbiota

Glyphosate is one of the most widely used herbicides globally. It acts by inhibiting an enzyme in an aromatic amino acid synthesis pathway specific to plants and microbes, leading to the view that it poses no risk to other organisms. However, there is growing concern that glyphosate is associated with health effects in humans and an ever-increasing body of evidence that suggests potential deleterious effects on other animals including pollinating insects such as bees. Although pesticides have long been considered a factor in the decline of wild bee populations, most research on bees has focussed on demonstrating and understanding the effects of insecticides. To assess whether glyphosate poses a risk to bees, we characterised changes in survival, behaviour, sucrose solution consumption, the digestive tract proteome, and the microbiota in the bumblebee Bombus terrestris after chronic exposure to field relevant doses of technical grade glyphosate or the glyphosate-based formulation, RoundUp Optima+®. Regardless of source, there were changes in response to glyphosate exposure in important cellular and physiological processes in the digestive tract of B. terrestris, with proteins associated with oxidative stress regulation, metabolism, cellular adhesion, the extracellular matrix, and various signalling pathways altered. Interestingly, proteins associated with endocytosis, oxidative phosphorylation, the TCA cycle, and carbohydrate, lipid, and amino acid metabolism were differentially altered depending on whether the exposure source was glyphosate alone or RoundUp Optima+®. In addition, there were alterations to the digestive tract microbiota of bees depending on the glyphosate source No impacts on survival, behaviour, or food consumption were observed. Our research provides insights into the potential mode of action and consequences of glyphosate exposure at the molecular, cellular and organismal level in bumblebees and highlights issues with the current honeybee-centric risk assessment of pesticides and their formulations, where the impact of co-formulants on non-target organisms are generally overlooked.

Specific immunity proteomic profile of the skin mucus of Antarctic fish Chionodraco hamatus and Notothenia coriiceps

The white-blooded Antarctic icefish is the only known vertebrate lacking oxygen-transporting haemoglobins. Fish skin mucus, as the first line of defence against pathogens, can reflect fish welfare. In this study, we analysed the skin mucus proteome profiles of the two Antarctic fish species, the white-blooded Antarctic icefish, Chionodraco hamatus, and the red-blooded Antarctic fish, Notothenia coriiceps, unfolding the different proteins by liquid chromatography coupled with tandem mass spectrometry isobaric tags for relative and absolute quantitation (iTRAQ) technology. Of the 4444 totally identified proteins, 227 differentially expressed proteins (DEPs) were found in the comparison between C. hamatus and N. coriiceps, of which 121 were upregulated and 106 were downregulated in the icefish. In the Kyoto Encyclopedia of Genes and Genomes pathway annotation, we found two pathways "Legionellosis" and "Complement and coagulation cascades" were significantly enriched, among of which innate immune candidate proteins such as C3, CASP1, ASC, F3 and C9 were significantly upregulated, suggesting their important roles in C. hamatus immune system. Additionally, the DEP protein-protein interaction network analysis and "Response to stress" GO category provided candidate biomarkers for deep understanding of the distinct immune response of the two Antarctic fish underlying the cold adaptation.

Post-translational protein deimination signatures in sea lamprey (Petromyzon marinus) plasma and plasma-extracellular vesicles

Lampreys are a jawless vertebrate species belonging to an ancient vertebrate lineage that diverged from a common ancestor with humans ~500 million years ago. The sea lamprey (Petromyzon marinus) has a filter feeding ammocoete larval stage that metamorphoses into a parasitic adult, feeding both on teleost and elasmobranch fish. Lampreys are a valuable comparative model species for vertebrate immunity and physiology due to their unique phylogenetic position, unusual adaptive immune system, and physiological adaptions such as tolerance to salinity changes and urea. Peptidylarginine deiminases (PADs) are a phylogenetically conserved enzyme family which catalyses post-translational deimination/citrullination in target proteins, enabling proteins to gain new functions (moonlighting). The identification of deiminated protein targets in species across phylogeny may provide novel insights into post-translational regulation of physiological and pathophysiological processes. Extracellular vesicles (EVs) are membrane vesicles released from cells that carry cargos of small molecules and proteins for cellular communication, involved in both normal and pathological processes. The current study identified deimination signatures in proteins of both total plasma and plasma-EVs in sea lamprey and furthermore reports the first characterisation of plasma-EVs in lamprey. EVs were poly-dispersed in the size range of 40-500 nm, similar to what is observed in other taxa, positive for CD63 and Flotillin-1. Plasma-EV morphology was confirmed by transmission electron microscopy. Assessment of deimination/citrullination signatures in lamprey plasma and plasma-EVs, revealed 72 deimination target proteins involved in immunity, metabolism and gene regulation in whole plasma, and 37 target proteins in EVs, whereof 24 were shared targets. Furthermore, the presence of deiminated histone H3, indicative of gene-regulatory mechanisms and also a marker of neutrophil extracellular trap formation (NETosis), was confirmed in lamprey plasma. Functional protein network analysis revealed some differences in KEGG and GO pathways of deiminated proteins in whole plasma compared with plasma-EVs. For example, while common STRING network clusters in plasma and plasma-EVs included Peptide chain elongation, Viral mRNA translation, Glycolysis and gluconeogenesis, STRING network clusters specific for EVs only included: Cellular response to heat stress, Muscle protein and striated muscle thin filament, Nucleosome, Protein processing in endoplasmic reticulum, Nucleosome and histone deacetylase complex. STRING network clusters specific for plasma were: Adipokinetic hormone receptor activity, Fibrinogen alpha/beta chain family, peptidase S1A, Glutathione synthesis and recycling-arginine, Fructose 1,6-bisphosphate metabolic process, Carbon metabolism and lactate dehydrogenase activity, Post-translational protein phosphorylation, Regulation of insulin-like growth factor transport and clotting cascade. Overall, for the EV citrullinome, five STRING network clusters, 10 KEGG pathways, 15 molecular GO pathways and 29 Reactome pathways were identified, compared with nine STRING network clusters, six KEGG pathways, two Molecular GO pathways and one Reactome pathway specific for whole plasma; while further pathways were shared. The reported findings indicate that major pathways relevant for immunity and metabolism are targets of deimination in lamprey plasma and plasma-EVs, with some differences, and may help elucidating roles for the conserved PAD enzyme family in regulation of immune and metabolic function throughout phylogeny.

Proteins of the Ciliated Protozoan Parasite Ichthyophthirius multifiliis Identified in Common Carp Skin Mucus

The skin mucus is the fish primary defense barrier protecting from infections via the skin epidermis. In a previous study, we have investigated the proteome of common carp (Cyprinus carpio) skin mucus at two different time points (1 and 9 days) post-exposure to Ichthyophthirius multifiliis. Applying a nano-LC ESI MS/MS technique, we have earlier revealed that the abundance of 44 skin mucus proteins has been differentially regulated including proteins associated with host immune responses and wound healing. Herein, in skin mucus samples, we identified six proteins of I. multifiliis associated with the skin mucus in common carp. Alpha and beta tubulins were detected in addition to the elongation factor alpha, 26S proteasome regulatory subunit, 26S protease regulatory subunit 6B, and heat shock protein 90. The identified proteins are likely involved in motility, virulence, and general stress during parasite growth and development after parasite attachment and invasion. Two KEGG pathways, phagosome and proteasome, were identified among these parasite proteins, mirroring the proteolytic and phagocytic activities of this parasite during host invasion, growth, and development, which represent a plausible host invasion strategy of this parasite. The results obtained from this study can support revealing molecular aspects of the interplay between carp and I. multifiliis and may help us understand the I. multifiliis invasion strategy at the skin mucus barrier. The data may advance the development of novel drugs, vaccines, and diagnostics suitable for the management and prevention of ichthyophthiriosis in fish.

Histopathological analysis of zebrafish after introduction of non-biodegradable polyelectrolyte microcapsules into the circulatory system

Polyelectrolyte microcapsules are among the most promising carriers of various sensing substances for their application inside the bloodstream of vertebrates. The long-term effects of biodegradable microcapsules in mammals are relatively well studied, but this is not the case for non-biodegradable microcapsules, which may be even more generally applicable for physiological measurements. In the current study, we introduced non-biodegradable polyelectrolyte microcapsules coated with polyethylene glycol (PMs-PEG) into the circulatory system of zebrafish to assess their long-term effects on fish internal organs with histopathologic analysis. Implantation of PMs-PEG was not associated with the formation of microclots or thrombi in thin capillaries; thus, the applied microcapsules had a low aggregation capacity. The progression of the immune response to the implant depended on the time and the abundance of microparticles in the tissues. We showed that inflammation originated from recognition and internalization of PMs-PEG by phagocytes. These microcapsule-filled immune cells have been found to migrate through the intestinal wall into the lumen, demonstrating a possible mechanism for partial microparticle elimination from fish. The observed tissue immune response to PMs-PEG was local, without a systemic effect on the fish morphology. The most pronounced chronic severe inflammatory reaction was observed near the injection site in renal parenchyma and within the abdominal cavity since PMs-PEG were administered with kidney injection. Blood clots and granulomatosis were noted at the injection site but were not found in the kidneys outside the injection site. Single microcapsules brought by blood into distal organs did not have a noticeable effect on the surrounding tissues. The severity of noted pathologies of the gills was insufficient to affect respiration. No statistically significant alterations in hepatic morphology were revealed after PMs-PEG introduction into fish body. Overall, our data demonstrate that despite they are immunogenic, non-biodegradable PMs-PEG have low potential to cause systemic effects if applied in the minimal amount necessary for detection of fluorescent signal from the microcapsules.

Transcriptional changes revealed genes and pathways involved in the deficient testis caused by the inhibition of alkaline ceramidase (Dacer) in Drosophila melanogaster

Sphingolipids are ubiquitous structural components of eukaryotic cell membranes which are vital for maintaining the integrity of cells. Alkaline ceramidase is a key enzyme in sphingolipid biosynthesis pathway; however, little is known about the role of the enzyme in the male reproductive system of Drosophila melanogaster. To investigate the impact of alkaline ceramidase (Dacer) on male Drosophila, we got Dacer deficiency mutants (MUs) and found they displayed apparent defects in the testis's phenotype. To profile the molecular changes associated with this abnormal phenotype, we performed de novo transcriptome analyses of the MU and wildtype (WT) testes; and revealed 1239 upregulated genes and 1102 downregulated genes. Then, six upregulated DEGs (papilin [Ppn], croquemort [Crq], terribly reduced optic lobes [Trol], Laminin, Wunen-2, collagen type IV alpha 1 [Cg25C]) and three downregulated DEGs (mucin related 18B [Mur18B], rhomboid-7 [Rho-7], CG3168) were confirmed through quantitative real-time polymerase chain reaction in WT and MU samples. The differentially expressed genes were mainly associated with catalytic activity, oxidoreductase activity and transmembrane transporter activity, which significantly contributed to extracellular matrix-receptor interaction, fatty acids biosynthesis as well as glycine, serine, and threonine metabolism. The results highlight the importance of Dacer in the reproductive system of D. melanogaster and provide valuable resources to dig out the specific biological functions of Dacer in insect reproduction.

Extracellular vesicles and post-translational protein deimination signatures in haemolymph of the American lobster (Homarus americanus)

The American lobster (Homarus americanus) is a commercially important crustacean with an unusual long life span up to 100 years and a comparative animal model of longevity. Therefore, research into its immune system and physiology is of considerable importance both for industry and comparative immunology studies. Peptidylarginine deiminases (PADs) are a phylogenetically conserved enzyme family that catalyses post-translational protein deimination via the conversion of arginine to citrulline. This can lead to structural and functional protein changes, sometimes contributing to protein moonlighting, in health and disease. PADs also regulate the cellular release of extracellular vesicles (EVs), which is an important part of cellular communication, both in normal physiology and in immune responses. Hitherto, studies on EVs in Crustacea are limited and neither PADs nor associated protein deimination have been studied in a Crustacean species. The current study assessed EV and deimination signatures in haemolymph of the American lobster. Lobster EVs were found to be a poly-dispersed population in the 10-500 nm size range, with the majority of smaller EVs, which fell within 22-115 nm. In lobster haemolymph, 9 key immune and metabolic proteins were identified to be post-translationally deiminated, while further 41 deiminated protein hits were identified when searching against a Crustacean database. KEGG (Kyoto encyclopedia of genes and genomes) and GO (gene ontology) enrichment analysis of these deiminated proteins revealed KEGG and GO pathways relating to a number of immune, including anti-pathogenic (viral, bacterial, fungal) and host-pathogen interactions, as well as metabolic pathways, regulation of vesicle and exosome release, mitochondrial function, ATP generation, gene regulation, telomerase homeostasis and developmental processes. The characterisation of EVs, and post-translational deimination signatures, reported in lobster in the current study, and the first time in Crustacea, provides insights into protein moonlighting functions of both species-specific and phylogenetically conserved proteins and EV-mediated communication in this long-lived crustacean. The current study furthermore lays foundation for novel biomarker discovery for lobster aquaculture.

Impact of high dietary plant protein with or without marine ingredients in gut mucosa proteome of gilthead seabream (Sparus aurata, L.)

The digestive tract, particularly the intestine, represents one of the main sites of interactions with the environment, playing the gut mucosa a crucial role in the digestion and absorption of nutrients, and in the immune defence. Previous researches have proven that the fishmeal replacement by plant sources could have an impact on the intestinal status at both digestive and immune level, compromising relevant productive parameters, such as feed efficiency, growth or survival. In order to evaluate the long-term impact of total fishmeal replacement on intestinal mucosa, the gut mucosa proteome was analysed in fish fed with a fishmeal-based diet, against plant protein-based diets with or without alternative marine sources inclusion. Total fishmeal replacement without marine ingredients inclusion, reported a negative impact in growth and biometric parameters, further an altered gut mucosa proteome. However, the inclusion of a low percentage of marine ingredients in plant protein-based diets was able to maintain the growth, biometrics parameters and gut mucosa proteome with similar values to FM group. A total fishmeal replacement induced a big set of underrepresented proteins in relation to several biological processes such as intracellular transport, assembly of cellular macrocomplex, protein localization and protein catabolism, as well as several molecular functions, mainly related with binding to different molecules and the maintenance of the cytoskeleton structure. The set of downregulated proteins also included molecules which have a crucial role in the maintenance of the normal function of the enterocytes, and therefore, of the epithelium, including permeability, immune and inflammatory response regulation and nutritional absorption. Possibly, the amino acid imbalance presented in VM diet, in a long-term feeding, may be the main reason of these alterations, which can be prevented by the inclusion of 15% of alternative marine sources. SIGNIFICANCE: Long-term feeding with plant protein based diets may be considered as a stress factor and lead to a negative impact on digestive and immune system mechanisms at the gut, that can become apparent in a reduced fish performance. The need for fishmeal replacement by alternative ingredients such as plant sources to ensure the sustainability of the aquaculture sector has led the research assessing the intestinal status of fish to be of increasing importance. This scientific work provides further knowledge about the proteins and biologic processes altered in the gut in response to plant protein based diets, suggesting the loss of part of gut mucosa functionality. Nevertheless, the inclusion of alternative marine ingredients was able to reverse these negative effects, showing as a feasible option to develop sustainable aquafeeds.

Proteomics for understanding pathogenesis, immune modulation and host pathogen interactions in aquaculture

Proteomic analyses techniques are considered strong tools for identifying and quantifying the protein contents in different organisms, organs and secretions. In fish biotechnology, the proteomic analyses have been used for wide range of applications such as identification of immune related proteins during infections and stresses. The proteomic approach has a significant role in understanding pathogen surviving strategies, host defence responses and subsequently, the fish pathogen interactions. Proteomic analyses were employed to highlight the virulence related proteins secreted by the pathogens to invade the fish host's defence barriers and to monitor the kinetics of protein contents of different fish organs in response to infections. The immune related proteins of fish and the virulence related proteins of pathogens are up or down regulated according to their functions in defence or pathogenesis. Therefore, the proteomic analyses are useful in understanding the virulence mechanisms of microorganisms and the fish pathogen interactions thereby supporting the development of new effective therapies. In this review, we focus and summarise the recent proteomic profiling studies exploring pathogen virulence activities and fish immune responses to stressors and infections.

Quantitative proteomic profiling of immune responses to Ichthyophthirius multifiliis in common carp skin mucus

Ichthyophthirius multifiliis, a ciliated protozoan parasite, causes ichthyophthiriasis and leads to considerable economic losses to the aquaculture industry. Understanding the fish immune response and host-parasite interactions could support developing novel strategies for better disease management and control. Fish skin mucus is the first line of defence against infections through the epidermis. Yet, the common carp, Cyprinus carpio, protein-based defence strategies against infection with I. multifiliis at this barrier remain elusive. The skin mucus proteome of common carp was investigated at 1 day and 9 days post-exposure with I. multifiliis. Using nano-LC ESI MS/MS and statistical analysis, the abundance of 19 immune related and signal transduction proteins was found to be differentially regulated in skin mucus of common carp in response to I. multifiliis. The analysis revealed increased abundance values of epithelial chloride channel protein, galactose-specific lectin nattection, high choriolytic enzyme 1 (nephrosin), lysozyme C, granulin and protein-glutamine gamma-glutamyltransferase 2 in I. multifiliis-exposed carp skin mucus. Multiple lectins and a diverse array of distinct serpins with protease inhibitor activity were identified likely implicated in lectin pathway activation and regulation of proteolysis, indicating that these proteins contribute to the carp innate immune system and the protective properties of skin mucus. The results obtained from this proteomic analysis enables a better understanding of fish host response to parasitic infection and gives insights into the key role skin mucus plays in protecting fish against deleterious effects of I. multifiliis.