Mast cell responses to Ergasilus (Copepoda), a gill ectoparasite of sea bream

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.

Teleost innate immunity, an intricate game between immune cells and parasites of fish organs: who wins, who loses

Fish, comprising over 27,000 species, represent the oldest vertebrate group and possess both innate and adaptive immune systems. The susceptibility of most wild fish to parasitic infections and related diseases is well-established. Among all vertebrates, the digestive tract creates a remarkably favorable and nutrient-rich environment, which, in turn, renders it susceptible to microparasites and macroparasites. Consequently, metazoan parasites emerge as important disease agents, impacting both wild and farmed fish and resulting in substantial economic losses. Given their status as pathogenic organisms, these parasites warrant considerable attention. Helminths, a general term encompassing worms, constitute one of the most important groups of metazoan parasites in fish. This group includes various species of platyhelminthes (digeneans, cestodes), nematodes, and acanthocephalans. In addition, myxozoans, microscopic metazoan endoparasites, are found in water-dwelling invertebrates and vertebrate hosts. It is worth noting that several innate immune cells within the fish alimentary canal and certain visceral organs (e.g., liver, spleen, and gonads) play active roles in the immune response against parasites. These immune cells include macrophages, neutrophils, rodlet cells, and mast cells also known as eosinophilic granular cells. At the site of intestinal infection, helminths often impact mucous cells number and alter mucus composition. This paper presents an overview of the state of the art on the occurrence and characteristics of innate immune cells in the digestive tract and other visceral organs in different fish-parasite systems. The data, coming especially from studies employed immunohistochemical, histopathological, and ultrastructural analyses, provide evidence supporting the involvement of teleost innate immune cells in modulating inflammatory responses to metazoan and protozoan parasitic infections.

Molecular characterization and phylogenetic analysis of parasitic copepoda; Ergasilus sieboldi isolated from cultured gilthead sea bream (Sparus aurata) in Egypt, associated with analysis of oxidative stress biomarkers

Parasitic copepods are common damaging ectoparasites of cultured marine fish that induce high mortalities in fish farms. The present study aimed to identify the cause of mass mortalities of cultured gilthead sea bream (Sparus aurata) as one of the highly valuable cultured marine fish species in Egypt. Parasitological examination demonstrated Ergasilus sieboldin (E. sieboldi) adult females of (1.3 ± 0.01 mm, n = 55) mean body length and (0.53 ± 0.04 mm) body width, lodged in the gill filaments of the forty examined fish with a pair of strong clawed antennae. The detected parasite has six segmented antennules and consists of cephalosome followed by four divided thoracic segments that narrow posteriorly, five pairs of swimming legs, genital segment, abdominal segments followed by furcal rami with unequal caudal setae and two egg sacs at the end of the body. The collected E. sieboldi were confirmed by molecular characterization and phylogenetic analysis based on 28S rDNA sequencing. The obtained sequence in this study was registered in the GenBank with (OM812074) accession number as a first sequence of E. sieboldi from Egypt. Oxidative stress biomarkers in the gills of the parasitized fish were evaluated to describe the host defense mechanisms against E. sieboldi infestation. The current study demonstrated decreasing in reduced glutathione (GSH) content and activity of the anti-oxidant enzyme catalase (CAT), as well as elevation in the level of malondialdehyde (MDA) due to exposure to oxidative damage that might have a role in the tissue damage and dysfunction.

Parasitic crustaceans (Branchiura and Copepoda) parasitizing the gills of puffer fish species (Tetraodontidae) from the coast of Campeche, Gulf of Mexico

New information on the marine parasitic crustaceans from the Campeche coast, Gulf of Mexico (GoM), can improve our baseline knowledge of the ecology of both the host and parasite by providing, for example, parameters of infection. Such knowledge is especially important for fish farming, so that appropriate quarantine measures can be established. Our aim was to morphologically identify the parasitic crustaceans infecting puffer fish of commercial importance in the coastal zone of Campeche, Mexico. We provide new information on four known species of parasitic crustaceans from 92 specimens representing five species of tetraodontid fish. The parasitic crustaceans Argulus sp. (Branchiura, Argulidae), Caligushaemulonis (Caligidae), Pseudochondracanthusdiceraus (Chondracanthidae), and Taeniacanthuslagocephali (Taeniacanthidae) (all Copepoda) were found on Lagocephaluslaevigatus, Sphoeroidesnephelus, S.parvus, S.spengleri, and S.testudineus. This study revealed the occurrence of P.diceraus, which is of importance in aquaculture, on Sphoeroidesannulatus in the Mexican Pacific. Additionally, our results and other documentary records provide the first evidence of the interoceanic occurrence of the same parasitic crustacean species in the south-southwest of Gulf of Mexico, the Atlantic Ocean, and the Pacific Ocean. Moreover, our study provides valuable information on the biodiversity of parasitic crustaceans present in the GoM on puffer fish which are of great commercial importance for human consumption, fisheries, and aquaculture.

Rodlet cells, fish immune cells and a sentinel of parasitic harm in teleost organs

Rodlet cells (RCs) are the enigmatic and distinctive pear-shaped cells had found in many tissues of marine and freshwater teleosts. They have a distinctive fibrous capsule or the cell cortex that envelopes conspicuous inclusions called rodlets, basally situated nucleus, and poorly developed mitochondria. The contraction of the cell cortex results in the expulsion of the cell contents through an apical opening. One hundred and thirty years since rodlet cells were first reported, many questions remain about their origin and a function. This review will present new evidence regarding the relationship between RCs and metazoan parasites, and a protozoan infecting organs of different fish species, and update the state of knowledge about the origin, structure and the function of these intriguing fish cells.

Severe Natural Outbreak of Cryptocaryon irritans in Gilthead Seabream Produces Leukocyte Mobilization and Innate Immunity at the Gill Tissue

The protozoan parasite Cryptocaryon irritans causes marine white spot disease in a wide range of fish hosts, including gilthead seabream, a very sensitive species with great economic importance in the Mediterranean area. Thus, we aimed to evaluate the immunity of gilthead seabream after a severe natural outbreak of C. irritans. Morphological alterations and immune cell appearance in the gills were studied by light microscopy and immunohistochemical staining. The expression of several immune-related genes in the gills and head kidney were studied by qPCR, including inflammatory and immune cell markers, antimicrobial peptides (AMP), and cell-mediated cytotoxicity (CMC) molecules. Serum humoral innate immune activities were also assayed. Fish mortality reached 100% 8 days after the appearance of the C. irritans episode. Gill filaments were engrossed and packed without any space between filaments and included parasites and large numbers of undifferentiated and immune cells, namely acidophilic granulocytes. Our data suggest leukocyte mobilization from the head kidney, while the gills show the up-regulated transcription of inflammatory, AMPs, and CMC-related molecules. Meanwhile, only serum bactericidal activity was increased upon infection. A potent local innate immune response in the gills, probably orchestrated by AMPs and CMC, is triggered by a severe natural outbreak of C. irritans.

Survival of metazoan parasites in fish: Putting into context the protective immune responses of teleost fish

Defence mechanisms of fish can be divided into specific and non-specific that act in concert and are often interdependent. Most fish in both wild and cultured populations are vulnerable to metazoan parasites. Endoparasitic helminths include several species of digeneans, cestodes, nematodes, and acanthocephalans. Although they may occur in large numbers, helminth infections rarely result in fish mortality. Conversely, some ectoparasites cause mass mortality in farmed fish. Given the importance of fish innate immunity, this review addresses non-specific defence mechanisms of fish against metazoan parasites, with emphasis on granulocyte responses involving mast cells, neutrophils, macrophages, rodlet cells, and mucous cells. Metazoan parasites are important disease agents that affect wild and farmed fish and can induce high economic loss and, as pathogen organisms, deserve considerable attention. The paper will provide our light and transmission electron microscopy data on metazoan parasites-fish innate immune and neuroendocrine systems. Insights about the structure and functions of the cell types listed above and a brief account of the effects and harms of each metazoan taxon to specific fish apparati/organs will be presented.

Effects of Fouling Management and Net Coating Strategies on Reared Gilthead Sea Bream Juveniles

Simple Summary

Fish farming strives to cover the increasing demand for aquatic food sources as a result of global population growth. As a primary sector industry, aquaculture profit margins are narrow. Fouling management is an issue and represents a significant part of the operational cost of this activity. Over the last 30 years, this problem has been approached from different perspectives and the use of copper dioxide to control fouling production has been the most successful strategy. However, far beyond being the definite solution, the use of copper involves several concerns, and so the aquaculture industry has been continuously trying to find a reliable alternative. Coating the nets and cleaning on-site was adopted by the industry as a realistic alternative around 2015. This work contrasts these two fouling management strategies, simulating real working conditions by analysing the results from different perspectives. The conclusions from this work suggest a combination of both as a promising future alternative.

Abstract

In aquaculture, biofouling management is a difficult and expensive issue. Cuprous oxide has been commonly used to prevent fouling formation. To cheapen net management and reduce the use of copper, the industry has proposed several alternatives. Currently, polyurethane coatings are being explored and commercially implemented. With this alternative, net cleaning is done in situ, reducing the number of nets necessary to raise a batch, thus ideally reducing operational costs. This pilot study compared this new strategy to the use of cuprous oxide. The results show that nets treated with antifouling perform better and bioaccumulation of copper in fish tissues do not pose health risks to fish. Alternatives involving on-site cleaning need to improve efficiency. Although the conditions of this work are not completely comparable to commercial aquaculture conditions, the results might indicate the strengths and constrains of the solutions tested in real life.

Histopathological changes and piscidin 5-like location in infected Larimichthys crocea with parasite Cryptocaryon irritans

Cryptocaryon irritans infection could cause huge economic losses to the marine fish industry. Larimichthys crocea, a special economic species in China, suffered from the threat of serious infection, and L. crocea could enhance the level of piscidin 5-like to defense against the infection. This study set out to observe the main histopathological changes of some key tissues caused by infection, and determineed how an ectoparasite affected the expression of piscidin-5 like in its hosts. Pathological changes and immune response were assessed using histological and in situ hybridization (ISH) technologies. The infection induced inflammation occurring, especially in the gill where epithelium cells swell, hyperplasia, necrosis shedding adjacent to the parasites attachment sites. Infected hepatic cells grown big vacuoles in the cytoplasm. The boundary between red pulp and white pulp turned indistinct, splenic corpuscle lost the normal structure, the number and size of melano-macrophage centers increased apparently in the infected spleen. The whole structure of head kidney became loose. Immunostaining with RNA probes against piscidin 5-like showed subpopulations of mast cells (MCs) were positive. Piscidin 5-like-positive MCs existed mainly in the head kidney where they distributed around melano-macrophage center, followed in the gill located at different positions they also distributed in the margin of spleen, and randomly and sparsely existed in the liver. After being infected by C. irritans, the gill arch arose positive MCs groups, and they also migrated to spleen, while the positive staining deepen in other detected tissues. Therefore, organism enhanced the expression level through improving expression ability of positive MCs, or increasing the number of positive MCs.

Pike intestinal reaction to Acanthocephalus lucii (Acanthocephala): immunohistochemical and ultrastructural surveys

Background

The Northern pike, Esox lucius, is a large, long-lived, top-predator fish species and occupies a broad range of aquatic environments. This species is on its way to becoming an important model organism and has the potential to contribute new knowledge and a better understanding of ecology and evolutionary biology. Very few studies have been done on the intestinal pathology of pike infected with helminths. The present study details the first Italian record of adult Acanthocephalus lucii reported in the intestine of E. lucius.

Results

A total of 22 pike from Lake Piediluco (Central Italy) were examined, of which 16 (72.7%) were infected with A. lucii. The most affected areas of gastrointestinal tract were the medium and distal intestine. The intensity of infection ranged from 1 to 18 parasites per host. Acanthocephalus lucii penetrated mucosal and submucosal layers which had a high number of mast cells (MCs) with an intense degranulation. The cellular elements involved in the immune response within the intestine of pike were assessed by ultrastructural techniques and immunohistochemistry using antibodies against met-enkephalin, immunoglobulin E (IgE)-like receptor (FCεRIγ), histamine, interleukin-6, interleukin-1β, substance P, lysozyme, serotonin, inducible-nitric oxide synthase (i-NOS), tumor necrosis factor-α (TNF-α) and the antimicrobial peptide piscidin 3 (P3). In intestines of the pike, several MCs were immunopositive to 9 out of the 11 aforementioned antibodies and infected fish had a higher number of positive MCs when compared to uninfected fish.

Conclusions

Pike intestinal tissue response to A. lucii was documented. Numerous MCs were seen throughout the mucosa and submucosal layers. In infected and uninfected intestines of pike, MCs were the dominant immune cell type encountered; they are the most common granulocyte type involved in several fish-helminth systems. Immunopositivity of MCs to 9 out of 11 antibodies is of great interest and these cells could play an important key role in the host response to an enteric helminth. This is the first report of A. lucii in an Italian population of E. lucius and the first account on positivity of MCs to piscidin 3 and histamine in a non-perciform fish.

Histopathological changes on the gills of asp (Aspius aspius) and European catfish (Silurus glanis) caused by Lamproglena pulchella and a Lamproglena sp. (Copepoda: Lernaeidae), respectively

In a parasitology survey of Hungarian fishes, heavy infections of parasitic copepods Lamproglena pulchella and a Lamproglena sp. were found in the gills of the asp and the European catfish, respectively. Individuals of both fish species were emaciated and infected with hundreds of Lamproglena. Copepods located close to the tip of gill filaments and formed a depression at the attachment sites. In histological sections, cell degenerations and local haemorrhages were present adjacent to the maxillipeds and where the maxillary claws pierced the gill tissue. Around maxillae and in the midgut of the Lamproglena, damaged piscine blood cells and remains of the gill tissue were observed. Host reaction was expressed by proliferation of epithelioid cells, increase in both number and size of goblet and mast cells and formation of giant cells.

Special dyeing, histochemistry, immunohistochemistry and ultrastructure: A study of mast cells/eosinophilic granules cells (MCs/EGC) from Centropomus parallelus intestine

Intestine mast cells/eosinophilic granule cells (MCs/EGC) of the marine species Centropomus parallelus (fat snook) were first studied using light and electron microscopy techniques. Mast cells are cells from the connective tissue found in almost all organs and tissues of vertebrates. In fish, they appear in greater numbers in parts of their bodies that are exposed to their environment, such as skin, gills and intestine. The granules in fat snook's mast cell contain a variety of substances, such as histamine, heparin, chondroitin sulfate, serotonin, proteases and cytokines. The present study of intestine MCs/EGC was carried out in 20 specimens of fat snook. Samples of tissue were fixed in Bouin solution and in buffered formalin. Ferric hematoxylin - Congo red, pH6 acridine orange, pH2.5 and pH0,5 Alcian Blue (AB), toluidine blue, PAS, AB + PAS and immunohistochemistry protocols were used. In the mucosa and submucosa layers, MCs/EGCs granules with basic contents were evidenced by Congo red staining, and with acid contents granules were identified through pH 2.5 and 0,5 AB, and acridine orange. Basic and acid contents were simultaneously evidenced using ferric hematoxylin - Congo red stain. Metachromasia was observed in both mucosal and submucosal mast cells. Neutral glycoproteins were evidenced by using PAS protocol, glycosaminoglycan through AB and both simultaneously through AB + PAS. In immunohistochemistry assays, MCs/EGC were positive for tryptase, chymase and serotonin. As in mammals, the study of samples fixed in modified Karnovsky for transmission electron microscopy evidenced that most of the MCs granules were spherical and showed varying electron density, as described in previous reports on other teleost fish species. The metachromasia observed and the identification of tryptase, chymase and serotonin suggest a great similarity between fat snook's MCs/EGC and those described in the mucosa of mammals.

Fish innate immunity against intestinal helminths

Most individual fish in farmed and wild populations are infected with parasites. Upon dissection of fish, helminths from gut are often easily visible. Enteric helminths include several species of digeneans, cestodes, acanthocephalans and nematodes. Some insights into biology, morphology and histopathological effects of the main fish enteric helminths taxa will be described here. The immune system of fish, as that of other vertebrates, can be subdivided into specific and aspecific types, which in vivo act in concert with each other and indeed are interdependent in many ways. Beyond the small number of well-described models that exist, research focusing on innate immunity in fish against parasitic infections is lacking. Enteric helminths frequently cause inflammation of the digestive tract, resulting in a series of chemical and morphological changes in the affected tissues and inducing leukocyte migration to the site of infection. This review provides an overview on the aspecific defence mechanisms of fish intestine against helminths. Emphasis will be placed on the immune cellular response involving mast cells, neutrophils, macrophages, rodlet cells and mucous cells against enteric helminths. Given the relative importance of innate immunity in fish, and the magnitude of economic loss in aquaculture as a consequence of disease, this area deserves considerable attention and support.

Occurrence of immune cells in the intestinal wall of Squalius cephalus infected with Pomphorhynchus laevis

A sub-population of 34 specimens of chub, Squalius cephalus, was sampled from the River Brenta (Northern Italy) and examined for ecto- and endo-parasites. Pomphorhynchus laevis (Acanthocephala) was the only enteric helminth encountered. Immunofluorescence and ultrastructural studies were conducted on the intestines of chub. Near the site of parasite's attachment, mucous cells, mast cells (MCs), neutrophils and rodlet cells (RCs) were found to co-occur within the intestinal epithelium. The numbers of mucous cells, MCs and neutrophils were significantly higher in infected fish (Mann-Whitney U test, p < 0.05). Dual immunofluorescence staining with the lectin Dolichos Biflorus Agglutinin (DBA) and the macrophage-specific MAC387 monoclonal antibody, with parallel transmission electron microscopy, revealed that epithelial MCs often made intimate contact with the mucous cells. Degranulation of a large number of MCs around the site of the acanthocephalan's attachment and in proximity to mucous cells was also documented. MCs and neutrophils were abundant in the submucosa. Immune cells of the intestinal epithelium have been described at the ultrastructural level and their possible functions and interactions are discussed.

Antimicrobial Peptides as Mediators of Innate Immunity in Teleosts

Antimicrobial peptides (AMPs) have been identified throughout the metazoa suggesting their evolutionarily conserved nature and their presence in teleosts is no exception. AMPs are short (18–46 amino acids), usually cationic, amphipathic peptides. While AMPs are diverse in amino acid sequence, with no two AMPs being identical, they collectively appear to have conserved functions in the innate immunity of animals towards the pathogens they encounter in their environment. Fish AMPs are upregulated in response to pathogens and appear to have direct broad-spectrum antimicrobial activity towards both human and fish pathogens. However, an emerging role for AMPs as immunomodulatory molecules has become apparent—the ability of AMPs to activate the innate immune system sheds light onto the multifaceted capacity of these small peptides to combat pathogens through direct and indirect means. Herein, this review focuses on the role of teleost AMPs as modulators of the innate immune system and their regulation in response to pathogens or other exogenous molecules. The capacity to regulate AMP expression by exogenous factors may prove useful in modulating AMP expression in fish to prevent disease, particularly in aquaculture settings where crowded conditions and environmental stress pre-dispose these fish to infection.

Histopathology and the inflammatory response of European perch, Perca fluviatilis muscle infected with Eustrongylides sp. (Nematoda)

BACKGROUND

The European perch, Perca fluviatilis L. is a common paratenic host of dioctophymatid nematodes belonging to the genus Eustrongylides. In this host, once infected oligochaetes, which serve as the first intermediate host, are ingested, Eustrongylides migrates through the intestine and is frequently encountered within the musculature, free within the body cavity, or encapsulated on the viscera. The current study details the first Italian record of Eustrongylides sp. with larvae reported in the muscle of P. fluviatilis.

METHODS

Uninfected and nematode-infected muscle tissues of perch were fixed and prepared for histological evaluation and electron microscopy. Some sections were subjected to an indirect immunohistochemical method using anti-PCNA, anti-piscidin 3 and anti-piscidin 4 antibodies.

RESULTS

A total of 510 P. fluviatilis (TL range 15-25 cm) from Lake Trasimeno, Perugia were post-mortemed; 31 individuals had encysted nematode larvae within their musculature (1-2 worms fish(-1)). Histologically, larvae were surrounded by a capsule with an evident acute inflammatory reaction. Muscle degeneration and necrosis extending throughout the sarcoplasm, sarcolemmal basal lamina, endomysial connective tissue cells and capillaries was frequently observed. Within the encapsulating reaction, macrophage aggregates (MAs) were seen. Immunohistochemical staining with the proliferating cell nuclear antigen (PCNA) revealed numerous PCNA-positive cells within the thickness of the capsule and in the immediate vicinity surrounding Eustrongylides sp. larvae (i.e. fibroblasts and satellite cells), suggesting a host response had been initiated to repair the nematode-damaged muscle. Mast cells (MCs) staining positively for piscidin 3, were demonstrated for the first time in response to a muscle-infecting nematode. The piscidin 3 positive MC's were seen principally in the periphery of the capsule surrounding the Eustrongylides sp. larva.

CONCLUSIONS

A host tissue response to Eustrongylides sp. larvae infecting the musculature of P. fluviatilis was observed. Numerous fibroblasts, MAs and MCs were seen throughout the thick fibroconnectival layer of the capsule enclosing larvae. PCNA positive cells within the capsule suggest that host repair of nematode damaged muscle does occur, while the presence of the antimicrobial peptide piscidin 3 is shown for the first time. This is first report of Eustrongylides sp. in an Italian population of P. fluviatilis.

Fine structure and cellular responses at the host-parasite interface in a range of fish-helminth systems

A series of ultrastructural-based studies were conducted on the interface region in different fish-helminth systems: (a) an intestinal infection of the cestode Monobothrium wageneri in tench, Tinca tinca; (b) an extensive intestinal submucosa and mucosal infection in tench by metacercariae of an unidentified digenean trematode; (c) an intestinal infection in brown trout, Salmo trutta, by the acanthocephalan Dentitruncus truttae; (d) an extraintestinal infection by larvae of the acanthocephalan, Pomphorhynchus laevis in three-spined sticklebacks, Gasterosteus aculeatus; and (e) an infection in the livers of Eurasian minnow, Phoxinus phoxinus, by larvae of the nematode Raphidascaris acus. Endoparasitic helminths frequently cause inflammation of the digestive tract and associated organs, inducing the recruitment of various immune cells to the site of infection. In each of the fish-helminth systems that were studied, a massive hyperplastic granulocyte response involving mast cells (MCs) and neutrophils in close proximity to the helminths was documented. The current study presents data on the interface region in each fish-helminth system and documents the penetration of mast cells granules within the tegument of P. laevis larvae. No extracellular vesicles containing tegumental secretions from any of the four different taxa of endoparasitic helminths species at the host-parasite interface region were seen.

Ultrastructural assessment of granulomas in the liver of perch (Perca fluviatilis) Infected by tapeworm

Granulomas caused by migration of larvae of a helminth parasite, Triaenophorus nodulosus, within the liver of perch (Perca fluviatilis) from Rimov Dam Lake (Czech Republic) were assessed by transmission electron microscopy. Lesions were found in the liver of 29 out of 34 perch examined (85.2%) and there were between 1 and 15 T. nodulosus larvae identified per host. Pathological changes were more severe in livers containing more granulomas. Within the granulomas, there were three concentric regions: an outer layer of fibrous connective tissue, a middle clear epithelioid layer and a central dark spindle cell layer. The outer layer contained mast cells, fibroblasts, thick collagen bundles and epithelioid cells. The granulomas contained few lymphocytes and macrophages. Hepatocytes adjacent to the granulomas showed pronounced degeneration (ranging from vacuolar degeneration to acute cellular swelling).

Occurrence of the parasitic copepod Ergasilus labracis on Threespine Sticklebacks from the south coast of Newfoundland

A study conducted from August to October 2013 surveyed Threespine Sticklebacks Gasterosteus aculeatus (n = 822) for the presence of parasitic copepods in the vicinity of large sea-cage salmonid farms in Bay d'Espoir, Newfoundland. The majority of parasitic copepods surveyed were Ergasilus labracis (n = 4,684). Other parasitic copepods observed on Threespine Sticklebacks during the survey included chalimus-stage Lepeophtheirus spp. (n = 3), adult Argulus alosae (n = 2), and a single Thersitina gasterostei. This represents a new host record for E. labracis. The copepods were present on fish collected in a broad range of temperatures (6.9-17.7°C) and salinities (10.2-30.2 [Practical Salinity Scale]). The parasitic copepods were most commonly found on larger hosts estimated to be age 1 or older. Surprisingly, the highest infestations (approximately 65%) were found on regions of the hosts outside of the gills (behind the pectoral fins and pelvic spines); in some cases, the copepods had inflicted significant damage to the skin of their hosts. Among host fish with evidence of an additional infection, such as microsporidian tumors (xenomas) or hemorrhagic-like symptoms (dark red abdomens and bloody mucus), the prevalence of E. labracis was significantly higher (43.4%) than among healthy fish (28.9%) despite there being no significant difference in size between the two fish health groups. In contrast, intensity (mean number of individual parasites per host) was significantly higher among healthy hosts (23.6) than among unhealthy ones (7.63). Although this parasite has been listed as present in Newfoundland previously, it has a broad host range and has been reported to be pathogenic to farmed salmonids. Therefore, its potential impact on wild and farmed fish populations around Newfoundland should not be underestimated.

Fish immune responses to parasitic copepod (namely sea lice) infection

Parasitic copepods, in particular sea lice, have considerable impacts upon global freshwater and marine fisheries, with major economic consequences recognized primarily in aquaculture. Sea lice have been a contentious issue with regards to interactions between farmed and wild populations of fish, in particular salmonids, and their potential for detrimental effects at a population level. The following discussion will pertain to aquatic parasitic copepod species for which we have significant information on the host-parasite interaction and host response to infection (Orders Cyclopoida, Poecilostomatoida and Siphonostomatoida). This review evaluates prior research in terms of contributions to understanding parasite stage specific responses by the host, and in many cases draws upon model organisms like Lepeophtheirus salmonis and Atlantic salmon to convey important concepts in fish responses to parasitic copepod infection. The article discusses TH1 and TH2-like host responses in light of parasite immunomodulation of the host, current methods of immunological stimulation and where the current and future work in this field is heading.

Mast cells in common wolffish Anarhichas lupus L.: ontogeny, distribution and association with lymphatic vessels

The morphology, ontogeny and tissue distribution of mast cells were studied in common wolffish(Anarhichas lupus L.) at the larval, juvenile and adult life stages using light and electron-microscopy and immunohistochemistry. Fish were sampled at 1 day, 1, 2, 3, 4, 8 and 12 weeks post-hatching in addition to 6 and 9 months and 2 years and older. From 8 weeks post-hatching, mast cells in common wolffish mainly appeared as oval or rounded cells 8-15 mm in diameter with an eccentrically placed, ovoid nucleus and filled with cytoplasmic granules up to 1.2 mm in diameter. Granules were refractile and eosinophilic to slightly basophilic in H&E and stained bright red with Martius-scarlet-blue and purple with pinacyanol erythrosinate in formalin-fixed tissues. Mast cells stained positive for piscidin 4 and Fc ε RI by immunohistochemistry. From 1 day to 4 weeks post-hatching, immature mast cell containing only a few irregularly sized cytoplasmic granules were observed by light and electron-microscopy in loose connective tissue of cranial areas. From 1 day post-hatching, these cells stained positive for piscidin 4 and Fc ε RI by immunohistochemistry. From 12 weeks post-hatching, mast cells showed a primarily perivascular distribution and were particularly closely associated with lymphatic vessels and sinuses. Mast cells were mainly located at the peripheral border of the adventitia of arteries and veins, while they were in intimate contact with the endothelium of the lymphatic vessels. Numerous mast cells were observed in the intestine. A stratum compactum, as described in salmonids, was not observed in wolffish intestine,nor were mast cells confined to a separate layer, a stratum granulosum. Lymphatic vessels consisting of endothelium, intimal connective tissue and a poorly developed basal lamina were observed in the intestine. Scanning electron microscopy was used to compare the structure and localization of intestinal mast cells of common wolffish and rainbow trout. Scanning electron microscopy also revealed endothelial surface features and confirmed the existence of three distinctly different types of vessels in the wolffish intestine. Rainbow trout mast cell granules appeared as intact globular structures while empty vacuoles were observed in common wolffish. Mast cells were closely associated with lymphatic vessels in common wolffish, but not in rainbow trout.

The mucosal immune system of fish: the evolution of tolerating commensals while fighting pathogens

The field of mucosal immunology research has grown fast over the past few years, and our understanding on how mucosal surfaces respond to complex antigenic cocktails is expanding tremendously. With the advent of new molecular sequencing techniques, it is easier to understand how the immune system of vertebrates is, to a great extent, orchestrated by the complex microbial communities that live in symbiosis with their hosts. The commensal microbiota is now seen as the "extended self" by many scientists. Similarly, fish immunologist are devoting important research efforts to the field of mucosal immunity and commensals. Recent breakthroughs on our understanding of mucosal immune responses in teleost fish open up the potential of teleosts as animal research models for the study of human mucosal diseases. Additionally, this new knowledge places immunologists in a better position to specifically target the fish mucosal immune system while rationally designing mucosal vaccines and other immunotherapies. In this review, an updated view on how teleost skin, gills and gut immune cells and molecules, function in response to pathogens and commensals is provided. Finally, some of the future avenues that the field of fish mucosal immunity may follow in the next years are highlighted.

Infestation and pathological alterations by Ergasilus sarsi (Copepoda) on the Tanganyika Killifish from Africa

A total of 204 Ergasilus sarsi, a copepod, were collected from Tanganyika Killifish Lamprichthys tanganicanus in Lake Tanganyika during March 2010. The prevalence was 86.40%, the mean intensity was 7.56, and the mean abundance was 6.38. Only 27 of the fish were infested, and the highest infestation on one fish was 29. Proliferation of mucus cells and lamellar fusion occurred. Haemorrhage due to blood vessel compression was noted. This is the first record of E. sarsi from Tanganyika Killifish. This study is also the first to provide a description of the pathological alterations caused by E. sarsi.

Piscidins in the intestine of European perch, Perca fluviatilis, naturally infected with an enteric worm

This study set out to determine how an enteric parasite, the thorny-headed worm Acanthocephalus lucii, affected the expression of antimicrobial peptides (piscidins) in its host population, the European perch (Perca fluviatilis) collected from Lake Piediluco in Central Italy. A total of 87 perch were examined; 44 (50.5%) were infected with A. lucii (1-18 worms fish(-1)). Pathological changes and immune response were assessed using histological, ultrastructural and immunohistochemical techniques. The acanthocephalans only penetrated the surficial zone of the intestinal wall and induced only slight inflammation. The main damage was destruction of the mucosal epithelium covering the villi adjacent to the parasite's attachment site, and included necrosis and degeneration. Infected intestine had numerous mast cells (MCs), often in close proximity to, and within, the capillaries, and were associated with fibroblasts of the submucosal layer. Mast cells were irregular in shape with a cytoplasm filled by numerous electron-dense, membrane-bounded granules. Immunostaining of intestine with antibodies against the antimicrobial peptides piscidin 3 and piscidin 4 showed subpopulations of MCs that were positive. Piscidin-positive MCs were mainly observed among the epithelial cells of the intestine, but also within the submucosa. In both uninfected and parasite-infected perch, the number of MCs positive for piscidin 4 was higher than those immunoreactive with piscidin 3 (p < 0.05). For both piscidins, there was no significant difference in the number of positive MCs between parasite-infected and uninfected intestine (p > 0.05). However, uninfected fish showed higher immunostaining intensity for piscidin 3 than infected conspecifics (p < 0.05).

Fish immune responses against endoparasitic nematodes - experimental models

Vertebrates mount a series of immune reactions when invaded by helminths but antihelmintic immune strategies allow, in many cases, the first invaders of the non-immune host to survive for prolonged periods, whereas subsequent larval invaders of the same parasite species face increased host resistance and thereby decreased colonization success. This concomitant immunity may represent a trade-off between adverse side effects (associated with killing of large helminths in the host tissue) and the need for future protection against invasion. Encapsulation and isolation of large live endoparasitic larvae may be associated with less pathology compared to coping with excess dead parasite tissue in host organs. Likewise, live adult nematodes may be accepted in tissues at a certain activity level for the same reasons. Various host cell receptors bind helminth molecules after which signal-transducing events lead to mobilization of specific reaction patterns depending on the combination of receptors and ligands involved. Both innate and adaptive responses (humoral and cellular) are prominent actors, but skewing of the Th1 lymphocyte response towards a Th2 type is a characteristic element of antihelminthic responses in mammalian hosts. Similar patterns may be expected also to occur in at least some fish species, such as salmonids, producing relevant cytokines, MHCII and CD4+ cells required for these lymphocyte subpopulations. Atlantic cod, Gadus morhua L., is without these immunological elements that indicate that alternative reaction pathways exist in at least some fish groups. Recent achievements within teleost immunology have made it possible to track these host responses in fish and the present work outlines the main immune reactions in fish against helminths and suggests three experimental fish models for exploration of these immune pathways in fish infected with nematodes.

Histological damage and inflammatory response elicited by Monobothrium wageneri (Cestoda) in the intestine of Tinca tinca (Cyprinidae)

BACKGROUND

Among the European cyprinids, tench, Tinca tinca (L.), and the pathological effects their cestodes may effect, have received very little or no attention. Most literature relating to Monobothrium wageneri Nybelin, 1922, a common intestinal cestode of tench, for example, has focused on aspects of its morphology rather than on aspects of the host-parasite interaction.

RESULTS

Immunopathological and ultrastructural studies were conducted on the intestines of 28 tench, collected from Lake Piediluco, of which 16 specimens harboured tight clusters of numerous M. wageneri attached to the intestinal wall. The infection was associated with the degeneration of the mucosal layer and the formation of raised inflammatory swelling surrounding the worms. At the site of infection, the number of granulocytes in the intestine of T. tinca was significantly higher than the number determined 1 cm away from the site of infection or the number found in uninfected fish. Using transmission electron microscopy, mast cells and neutrophils were frequently observed in close proximity to, and inside, the intestinal capillaries; often these cells were in contact with the cestode tegument. At the host-parasite interface, no secretion from the parasite's tegument was observed. Intense degranulation of the mast cells was seen within the submucosa and lamina muscularis, most noticeably at sites close to the tegument of the scolex. In some instances, rodlet cells were encountered in the submucosa. In histological sections, hyperplasia of the mucous cells, notably those giving an alcian blue positive reaction, were evident in the intestinal tissues close to the swelling surrounding the worms. Enhanced mucus secretion was recorded in the intestines of infected tench.

CONCLUSIONS

The pathological changes and the inflammatory cellular response induced by the caryophyllidean monozoic tapeworm M. wageneri within the intestinal tract of an Italian population of wild tench is reported for the first time.