Search

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 lesions due to third-larval stage of nematode Brevimulticaecum sp. within the liver of a subpopulation of 31 Gymnotus inaequilabiatus from the Pantanal Region (Brazil) were studied with histochemical and immunohistochemical methods. In 93.5% of fish, livers harboured nematode larvae and the intensity of infection ranged from 8 to 293. In livers with highest number of larvae, the hepatic tissue was occupied primarily by the nematodes. Each larva was encircled by focal inflammatory granulomatous reaction. Within the thickness of the granuloma, three concentric layers were recognized: an inner layer of densely packed epithelioid cells, a middle layer of mast cells (MCs) entrapped in a thin fibroblast-connective mesh and an outer layer of fibrous connective tissue with fibroblasts. Epithelioid cells and fibroblasts within the thickness of the granuloma wall were positive for proliferative cell nuclear antigen (PCNA). Moreover, several hepatocytes in infected liver were immunoreactive to PCNA. Occurrence of rodlet cells and MCs in parenchyma, in close proximity to the encysted nematode larvae and near the blood vessel of infected liver, was observed. Macrophage aggregates (MAs) were numerous within the granulomas and scattered in parenchyma of the infected liver. High quantity of haemosiderin was encountered in MAs and hepatocytes of infected liver., (© 2017 John Wiley & Sons Ltd.)

The European eel, Anguilla anguilla, is a major warm-water fish species cultured in North and South Europe. Seventy-one A. anguilla collected between 2010 and 2015 from the Comacchio lagoons were examined. Fish were infected and damaged by larvae (L3) of the nematode Contracaecum rudolphii A, which were encapsulated within the thickness of the intestinal wall and within the external visceral peritoneum (serosa). Conspicuous granulomas, visible at sites of infection, were arranged in a trilayer, formed by a series of concentric whorls. The cells involved in the immune response and their distribution in the granuloma layers were assessed by immunohistochemical, immunofluorescence, and ultrastructural techniques. The outer part of the granuloma contained macrophages, macrophage aggregates, and mast cells (MCs) scattered among fibroblasts. This layer was vascularized, with degranulation of MCs occurring in close proximity to the capillaries. The middle layer was rich in MCs and fibroblasts. The inner layer, closest to the parasite larva, consisted mainly of dark epithelioid cells, some of which were necrotic. Non-necrotic epithelioid cells formed desmosomes between themselves or with fibroblasts. Within the granulomas, numerous cells of different types were positive to proliferative cell nuclear antigen antibody, indicating a high degree of cellular proliferation around the larvae., (© 2016 John Wiley & Sons Ltd.)

Background: A survey on endoparasitic helminths from freshwater fishes in the Pantanal Region (Mato Grosso do Sul, Brazil) revealed the occurrence of third-larval stage of the nematode Brevimulticaecum sp. (Heterocheilidae) in most organs of Gymnotus inaequilabiatus (Gymnotidae) also known by the local name tuvira. The aim of the present study was to examine Brevimulticaecum sp.-infected tuvira liver at the ultrastructural level and clarify the nature of granulomas and the cellular elements involved in the immune response to nematode larvae., Methods: Thirty-eight adult specimens of tuvira from Porto Morrinho, were acquired in January and March 2016. Infected and uninfected liver tissues were fixed and prepared for histological and ultrastructure investigations., Results: The prevalence of infection of tuvira liver by the nematode larvae was 95 %, with an intensity of infection ranging from 4 to 343 larvae (mean ± SD: 55.31 ± 73.94 larvae per liver). In livers with high numbers of nematode larvae, almost entire hepatic tissue was occupied by the parasites. Hepatocytes showed slight to mild degenerative changes and accumulation of pigments. Parasite larvae were surrounded by round to oval granulomas, the result of focal host tissue response to the infection. Each granuloma was typically formed by three concentric layers: an outer layer of fibrous connective tissue with thin elongated fibroblasts; a middle layer of mast cells entrapped in a thin fibroblast-connective mesh; and an inner layer of densely packed epithelioid cells, displaying numerous desmosomes between each other. Numerous macrophage aggregates occurred in the granulomas and in the parenchyma., Conclusions: Our results in tuvira showed that the larvae were efficiently sequestered within the granulomas, most of the inflammatory components were confined within the thickness of the granuloma, and the parenchyma was relatively free of immune cells and without fibrosis. Presumably this focal encapsulation of the parasites permits uninfected portions of liver to maintain its functions and allows the survival of the host.

Histopathology, histochemistry and immunohistochemistry of the integument of European eel, Anguilla anguilla (Linnaeus, 1758), infected by Myxidium sp. are reported. Skin samples from affected and unaffected eels were dissected, formalin fixed, paraffin embedded, sectioned and stained with H&E, Periodic acid-Schiff's staining method, Alcian Blue 8 GX pH 2.5/Periodic acid-Schiff's and McCallum-Goodpasture's Gram stain. Moreover, immunohistochemistry was performed using a primary polyclonal laminin antibody. Histologically, cysts (diameter 2-3 mm) were observed mainly under the scale pockets, encircled by a thin collagen layer, lined by elongated, flattened fibroblasts and containing bipolar, PAS- and Gram-positive spores with opposite polar capsules. The epidermis stretched by the underlying cyst appeared dysplastic, thinned with a significant reduction in mucous cells number. Only inconsistent and aspecific inflammatory reaction was noted around the cysts at the dermis/epidermis interface. Intense laminin-like protein immunolabel was documented in the plasmodial ectoplasm and related to host anergia. This was the first report of laminin immunolabel in a member of the Myxozoa. Epidermal dysplasia represents likely an aspecific response against the underlying tensile force exerted by the developing parasite cyst, while fibroblast and collagen encapsulation denote a parasite-driven host response protecting, rather than harming, the encircled parasite., (© 2015 John Wiley & Sons Ltd.)

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., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

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., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

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.

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)., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Histopathological lesions caused by plerocercoids of Triaenophorus nodulosus within the liver of perch, Perca fluviatilis, from Lake Trasimeno were studied. Livers harbored 1-3 parasite larvae and pathological alterations were more marked in those with 3 plerocercoids. In the liver, larvae were encysted, surrounded by a capsule of host tissue; two of 14 plerocercoids were necrotic. In infected livers, some hepatocytes showed degenerative changes, i.e. swelling and hydropic degeneration, notably those in close proximity to larvae. By comparison, hepatocytes in uninfected livers or in regions away from the point of infection appeared normal. The occurrence of macrophage aggregates (MAs) distributed among the mast cells (MCs) was observed around the encysted larvae. The cellular elements involved in the immune response within liver were assessed by immunohistochemical techniques and by the use of antibodies against the antimicrobial peptides piscidins 3 and 4, which revealed a sub-population of positive MCs. In infected livers, numerous MCs that were immunopositive to P4 and a few that were positive to P3 were found around T. nodulosus larvae. Histological sections of both uninfected and infected liver were immunostained with proliferative cell nuclear antigen (PCNA) antibody. Within the capsule and in close proximity to the parasite larvae, various cell types (i.e., MCs, fibroblasts and epithelioid cells) and a significantly higher number of PCNA-positive hepatocytes that were immunoreactive to PCNA were found compared to uninfected livers (ANOVA, P<0.05). No parasites of any type were found in gill, spleen, kidney or gonad of P. fluviatilis and the intestine of 3 perch were infected with few specimens of Acanthocephalus lucii., (Copyright © 2013 Elsevier B.V. All rights reserved.)

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)., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Immunohistochemical and ultrastructural studies were conducted on the gills of gilthead seabream, Sparus aurata L., naturally infected with the copepod ectoparasite Ergasilus lizae (Krøyer, 1863) in order to assess pathology and the host immune cell response. Gills of 56 gilthead seabream were screened for ectoparasites; 36 specimens (64.3%) harbored E. lizae. Intensity of infection was 32.7 ± 8.7 (mean ± SE). Pathological alterations to the gills of the host were more pronounced in close proximity to the copepod site of attachment. The parasite attached to the gills by means of its modified second antennae, occluded the arteries, provoked epithelial hyperplasia and hemorrhages and most often caused lamellar disruption. Numerous granular cells were encountered near the site of E. lizae attachment. In both infected and uninfected gills, the granular cells lay within the filaments and frequently occurred within the connective tissue inside and outside the blood vessels of the filaments. The type of granular cell was identified by immunohistochemical staining by using the monoclonal antibody G7 (mAb G7), which specifically recognizes acidophilic granulocytes (AGs) of S. aurata and with an anti-histamine antibody (as a marker for mast cells, MCs) on sections from 13 uninfected gills and 21 parasitized gills. The use of mAb G7 revealed that, in gills harboring copepods, the number of G7-positive cells (i.e., AGs; 32.9 ± 3.9, mean number of cells per 45,000 μm2 ± SE) was significantly higher than the density of the same cells in uninfected gills (15.3 ± 3.8; ANOVA, P < 0.05). Few histamine-positive granular cells (i.e., MCs) were found in the uninfected and parasitized gills. Here, we show, for the first time in S. aurata infected gills, that AGs rather than MCs are recruited and involved in the response to E. lizae infection in seabream.

Histopathological and ultrastructural investigations were conducted on 36 tench, Tinca tinca (L.), from Lake Trasimeno (Italy). The gills, intestine, liver, spleen, kidney and heart of 21 individuals were found to harbour an extensive infection of larvae of an unidentified digenean trematode. The eyes, gonads, swim bladder and muscles were uninfected. The parasites in each tissue type were embedded in a granulomatous proliferation of tissue, forming a reactive fibroconnective capsule around each larva. Most of the encysted larvae were metacercariae, in a degenerative state, but on occasion some cercariae were found. Many of the granulomas were either necrotic or had a calcified core. Within the granuloma of each, the occurrence of granulocytes, macrophages, rodlet cells and pigment-bearing macrophage aggregates was observed. Hearts bore the highest parasitic infection. Whilst the presence of metacercariae within the intestine was found positioned between the submucosa and muscle layers, metacercariae in the liver were commonly found encysted on its surface where the hepatocytes in close contact with the granuloma were observed to have electron-lucent vesicles within their cytoplasm. Metacercariae encysting adjacent to the cartilaginous rods of gill filaments were seen to elicit a proliferation of the cartilage from the perichondrium. Rodlet cells, neutrophils and mast cells were frequently observed in close proximity to, and within, infected gill capillaries. Given the degenerated state of most granulomas, a morphology-based identification of the enclosed digeneans was not possible., (© 2013 John Wiley & Sons Ltd.)

Background: Changes in the production of proliferating cell nuclear antigen (PCNA), a 36 kd protein involved in protein synthesis, within intestinal epithelia can provide an early indication of deviations to normal functioning. Inhibition or stimulation of cell proliferation and PCNA can be determined through immunohistochemical staining of intestinal tissue. Changes in the expression of PCNA act as an early warning system of changes to the gut and this application has not been applied to the fields of aquatic parasitology and fish health. The current study set out to determine whether a population of wild brown trout, Salmo trutta trutta (L.) harbouring an infection of the acanthocephalan Dentitruncus truttae Sinzar, 1955 collected from Lake Piediluco in Central Italy also effected changes in the expression of PCNA., Methods: A total of 29 brown trout were investigated, 19 of which (i.e. 65.5%) were found to harbour acanthocephalans (5-320 worms fish-1). Histological sections of both uninfected and infected intestinal material were immunostained for PCNA., Results: The expression of PCNA was observed in the epithelial cells in the intestinal crypts and within the mast cells and fibroblasts in the submucosa layer which is consistent with its role in cell proliferation and DNA synthesis. The number of PCNA-positive cells in both the intestinal epithelium and the submucosa layer in regions close to the point of parasite attachment were significantly higher than the number observed in uninfected individuals and in infected individuals in zones at least 0.7 cm from the point of parasite attachment (ANOVA, p < 0.05)., Conclusions: An infection of the acanthocephalan D. truttae within the intestinal tract of S. t. trutta effected a significant increase in the number of PCNA positive cells (mast cells and fibroblasts) at the site of parasite attachment when compared to the number of positive cells found in uninfected conspecifics and in tissue zones away from the point of parasite attachment.

The histopathology, ultrastructure, and immunohistochemistry of the alimentary canal of flounder Platichthys flesus (L.), naturally infected with the nematode Anisakis simplex s.l. (Rudolphi 1809) from the River Forth (Scotland), were investigated and described. Eight of the 16 flounders were infected with A. simplex s.l. larvae (L3); parasites were encapsulated by serosa on the external surface of the host's digestive tract (intensity of infection 1-8 parasites per host), although nematode larvae were found encysted under the peritoneal visceral serosa of the host spleen and liver and, occasionally, in the liver parenchyma (intensity of infection 3-10 parasites per host). In all sites, different structural elements were recognized within the capsule surrounding larvae. Among the epithelial cells of the intestine of 5 flounders with larvae encysted on external surface of the gut, the presence of several rodlet cells (RCs) was observed. Furthermore, often the occurrence of macrophage aggregates (MAs) was noticed in infected liver and spleen, mainly around the parasite larvae. Eight neuropeptide antisera were tested with immunohistochemistry methods on gut sections of 4 P. flesus infected with extraintestinal nematodes. Sections from the gut of 5 uninfected flounder were used for comparative purposes. In the tunica mucosa of parasitized P. flesus, several endocrine epithelial cells were immunoreactive to anti-CCK-39 (cholecystokinin 39) and -NPY (neuropeptide Y) sera; furthermore, in the myenteric plexus, a high number of neurons were immunoreactive to antibombesin, -galanin, and several to -NPY and -PHI (peptide histidine isoleucine) sera.

The mortality of juvenile European sea bass, Dicentrarchus labrax (L.), in the spring of the last 5 years in the northern coast of the Adriatic Sea has been attributed to heavy infections of the gill monogenean Diplectanum aequans (Wagener 1857) Diesing 1858. The histopathological examination of 38 sets of gills from hosts measuring 16.46 +/- 0.26 cm in total length (mean+/-S.E.) and weighing 45.98 +/- 2.37 g (mean+/-S.E.) were conducted using light and transmission electron microscopy. Twenty-eight (73.6%) D. labrax specimens were infected (34.61 +/- 4.42, mean intensity+/-S.E.; 5-100, range) with the majority of D. aequans attaching to the median and apical portions of the primary gill filaments. The sites of attachment were marked by the common presence of haemorrhages and a white mucoid exudate. In histological sections, the opisthaptors of the parasites were observed to penetrate deeply, lying in close proximity to the basal membrane of primary lamella where they induced a hyperplastic response. Disruption and fusion of the secondary lamellae were common in all infected specimens with several individuals also exhibiting a marked erosion and inflammation of the epithelium of the primary and secondary lamellae. In infected fish, cellular changes in the epithelium underlying the bodies of worms were noted typified by an elevation in the number of mucous and rodlet cells and a reduction in the number of chloride cells.

Histopathological, ultrastructural and immunohistochemical investigations were conducted on 26 specimens of powan Coregonus lavaretus (L.) from Loch Lomond (Scotland). The hearts of all 26 powan (15 females and 11 males) investigated harboured metacercariae of the digenean trematode Ichthyocotylurus erraticus (Rudolphi, 1809). The vast majority of metacercariae were located either singly or as an aggregation of white cysts on the surface of the bulbus arteriosus. The intensity of infection ranged from 2 to 200 larvae heart(-1), although the number of metacercariae found on male powan did not exceed 13. Histochemically, the parasite cyst wall gave a strong positive reaction with periodic acid schiff (PAS) and a faint positive signal with Azan-Mallory stain. All the metacercariae cysts were embedded in a granulomatous proliferation of heart epicardium tissue, forming a reactive fibroconnective capsule around the parasite. The capsule enclosing the parasite (produced by the host's reaction to the parasite) measured 13.57 to 90.20 microm (37.43 +/- 3.56) in thickness. Within the capsule wall, eosinophilic granular cells (EGCs), granulocytes, melanocytes and, in some instances, partially degenerated or vacuolated epithelioid cells were observed in close proximity to the cyst wall. Pigment-bearing macrophages were scattered throughout the granulomatous host-tissue reaction and as macrophage aggregates (MAs) within the capsules surrounding parasites. Immunohistochemical tests were applied to infected heart sections using 12 different antisera. Nerve fibres immunoreactive to bombesin, substance P (SP), and atrial natriuretic peptide (ANP) antisera were observed in close proximity to the parasite larvae. The presence of a serotonin-like substance was also observed within host immune-cells surrounding trematode cysts. Large cells of the epicardium were found to be immunoreactive to met-enkephalin and vasoactive intestinal peptide (VIP) antisera but not immunoreactive to anti-protein gene-product 9.5 (PGP9.5) sera.

Twenty sea bass Dicentrarchus labrax L. from a fish farm (floating cage) in Greece were examined for the presence of parasites. The gills of 7 (35%) fish were infected with adult female specimens of the parasitic copepod Lernanthropus kroyeri van Beneden, 1851, and the intensity of infection ranged from 1 to 24 parasites per host. The most infected portion of the gills appeared to be the primary lamellae. Erosion, desquamation and necrosis of the secondary lamellae were noticed near the site of copepod attachment; furthermore, the terminal claw of the second antennae lacerated tissue and vessels of infected gill. Parasitism by L. kroyeri affected the host's condition factor (mean +/- SE in uninfected vs parasitized; 1.88 +/- 0.04 vs 1.66 +/- 0.12; p < 0.05).

Immunohistochemical, ultrastructural and pathological studies were carried out on the gills of bream Abramis brama (L.) from Lake Mondsee, Austria, that were naturally infected with Ergasilus sieboldi Nordmann, 1832. Of a total of 14 specimens of bream examined, the gills of 7 (50%) were parasitized with this copepod and the intensity of infection ranged from 1 to 23 crustaceans per host. Histopathological investigations of infected gill showed extensive tissue damage due to attachment and feeding of the crustacean. Parasites attached close to the base of filaments near the gill arch. Pressure exerted by the ectoparasite attached to the lateral margin of the gill filaments induced atrophy of the secondary lamellae. Tissue reactions included hyperplasia and mucous cell proliferation of the respiratory epithelium. Mucous cells displayed an intense immunohistochemical reactivity with the anti-nitric oxide synthase antibody. In parasitized primary and secondary lamellae, a high number of eosinophilic granular cells and rodlet cells were noticed. Rodlet cells represent an inflammatory cell type closely linked to other piscine inflammatory cells. Presence of a high number of inflammatory cells at the site of E. sieboldi attachment is related to intense host cellular reaction.

Rodlet cells (RCs), and other inflammatory cells, namely eosinophile granule cells (EGCs), eosinophilic granulocytes and epithelioid cells in the liver, pancreas and peritoneal serosa of uninfected and naturally parasitized minnow Phoxinus phoxinus (Linnaeus, 1758), were studied by light and electron microscopy. Forty-eight minnows were examined and in 18 fishes encysted larvae of the nematode Raphidascaris acus (Bloch, 1779) were encountered, mainly in the pancreas. The number of larvae in the latter organ ranged from 2 to 46. Nematode larvae were encapsulated by epithelioid granulomata, and these cells displayed typical epithelial characteristics such as desmosomes and tonofilaments. EGCs and RCs characteristically surrounded the reactive foci and were suggestive of an integrated inflammatory network involving both cell types. In many instances RCs were noticed at the periphery of the pancreas, beneath the peritoneal serosa, partially or entirely surrounded by mesothelial cells. In the latter situation partially damaged RCs were present in the splancnic cavity entirely surrounded but not truly phagocytized (no phagolysosome occurred) by mesothelial cells, which shared the same ultrastructural features of epithelioid cells. This phenomenon has never been described and may represent a peculiar turnover of RCs in the pancreas likely related to the high sensitivity to damage. A significant difference (p < 0.01) in the number of RCs between uninfected and parasitized fish was noticed in the liver and pancreas. The data suggest that RCs represent an inflammatory cell type closely linked to other piscine inflammatory cells, such as EGCs, epithelioid cells and mesothelial cells.

A branchial osteogenetic neoplasm affecting a barbel Barbus barbus plebejus (Valenciennes, 1829) is described. The osteoblasts' pleomorphism, the lack of a well-developed and complete separation, the presence of eccentric, terminal proliferative edges infiltrating the lining tissues and the abundant tumour matrix suggest a histopathological diagnosis of a 'productive osteoblastic osteosarcoma'. The occurrence of eosinophilic granule cells (EGCs) scattered among neoplastic tissue is discussed in relation to the neoplastic growth and the inflammatory reaction, with reference to recent discoveries in mammalian mast cell biology.

Studies the histopathology of the alimentary canal of Anguilla anguilla L. associated with digenetic trematodes. Fine structure of the host-parasite interface; Occurrence of different types of cells in various stages of degeneration within the ventral sucker of Helicometra fasciata; Usefulness of electron microscopy in the identification of host cells associated with the parasites.

Focuses on the use of immuno-histochemical technique to demonstrate the transition form of a squamous cell carcinoma in a mirror carp, Cyprinus carpio L. Evaluation of the papillomatous elements in carinomas; Application of immunohistochemical methods on normal and neoplastic fish tissues; Characterization of the different cell types.