Ultrastructure and cytochemistry study of Goussia sparis (Protozoa: Apicomplexa) stages from the intestine of the gilthead sea bream Sparus aurata L. (Pisces: Teleostei)

 The ultrastructure and cytochemistry of merogonial and gamogonial stages and early unsporulated oocysts of Goussia sparis in the intestine of Sparus aurata were studied. The typical pellicle was observed in some stages. The different stages might appear in intraepithelial or supraepithelial positions, but they were always intracellular. First steps of two apparently different endomerogonies were observed in intra- and supraepithelial positions, respectively. An apparent ectomerogony also occurred in supraepithelial stages. Developing macrogamonts showed surface invaginations and were densely packed with ribosomes, well-developed rough endoplasmic reticulum, mitochondria, amylopectin granules, lipidic droplets, and wall-forming-like bodies. The latter could participate in the formation of the oocyst wall. Abundant and large mitochondria, together with residual nuclei, appeared in advanced microgamonts. Microgametes showed two flagella with microtubul arranged according to the typical pattern. An increase in polysaccharide content was observed with coccidian development, reaching a maximum in zygotes and unsporulated oocysts. Received: 30 January 1996 / Accepted: 8 July 1996     

The morphology of Ichthyophonus sp. in their mugilid hosts (Pisces: Teleostei) and following cultivation in vitro. A light and electron microscopy study

The morphology of Ichthyophonus sp., a parasite of Mugil capito and Liza saliens, was investigated by light and transmission electron microscopy. The most frequent stage found in the fish hosts was the multinucleate spore, though germinating stages, hyphae, and endospores were also found. Different development patterns were observed in the media assayed for in vitro culture. Optimal growth and development were obtained in Eagle's minimum essential medium (MEM) supplemented with 10% fetal bovine serum at pH 7. Ultrastructural features of multinucleate spores, both in the fish host and in culture, were a fibrillar thick wall and an electron-lucent matrix, with large glycogen granules, some electron-dense bodies, large vacuoles, lipid inclusions, and endoplasmic reticulum mainly appearing among the nuclei. Mitochondria with scarce tubulovesicular cristae were observed in the different stages, mainly near the wall and the germinating sites. Condensed heterochromatin was rarely seen. A nucleus-associated organelle (NAO) was frequently observed, and dictyosome cisternae and vesicles appeared in its vicinity. Received: 12 November 1998 / Accepted: 9 January 1999     

Electron microscopy studies on the a -bacteroids in the fat bodies of the lantern bug Pyrops candelaria Linn. (Homoptera: Fulgoridae)

The ultrastructure of a-bacteroids in relation to the fat-body cells of the lantern bug Pyrops candelaria was described. The fat-body-cell cytoplasm contained numerous mitochondria, rough endoplasmic reticula, vacuoles, and storage granules. Its nucleus had scattered chromatin materials. The a-bacteroid was enveloped by three membrane layers, namely, the plasma membrane, the cell wall, and the membrane envelope. Its cytoplasm contained amorphous dense bodies. The bacteroid reproduced by binary fission. Tracheoles were also found among fat-body cells. Received: 6 November 1996 / Accepted: 25 November 1996     

The fine structure of the endogenous stages of Eimeria labbeana

Summary The fine structure of the feeding organelles of the endogenous developmental stages of Eimeria labbeana from the ileal mucosa of the common Pigeon, Columba livia, is described and compared with similar structures of other species of Eimeria. Intra-cytoplasmic, membrane-bound vesicles of varying shapes and dimensions, and pinocytotic vesicle, were seen in association with cup-chaped or v-shaped invaginations in early schizonts, early macrogamonts, and macrogametes. Deep invaginations, averaging 1.7×0.5 in size, and found on the surface of early schizonts, early and young macrogamonts, and developing microgamonts, apparently function as organelles of ingestion and breakdown of host-cell cytoplasm. Micropores were rarely seen in schizonts and never in microgametes. The merozoite had one typical micropore (850×680 Å) and a number of micropore-like invaginations. Micropores of the microgamonts averaged 610×580 Å, and those of macrogamonts and macrogametes averaged 1,220×780 Å. A typical micropore was observed in an early oocyst. Intravacuolar tubules, each 580 Å in diameter and composed of nine microtubule-like subunits, were observed only in about 1 per cent of the more than 4,000 macrogametes studied. This paper establishes that E. labbeana is a species that possesses all the known eimerian organelles associated with feeding, expect the intravacuolar folds.Abbreviations for all Figures c channel - g Golgi body - h Host cell - hc Host cell cytoplasm - hn Host cell nucleus - hmi Host cell mitochondria - i Invagination - im Inner membrane - it Intravacuolar tubules - lh Limiting membrane of the host cell - lp Limiting membrane of the parasite - mg Microgamont - mp Micropore - n Nucleus - nu Nucleolus - o Oocyst - om Outer membrane - ow Oocyst wall - p Pellicle - pv Parasitophorous vacuole - pcv Pinocytotic vesicle - v Vesicle A portion of the author's postdoctoral research conducted at the Department of Biology of Boston University.     

Ceratomyxa sparusaurati (Protozoa: Myxosporea) infections in cultured gilthead sea bream Sparus aurata (Pisces: Teleostei) from Spain: aspects of the host-parasite relationship

Ceratomyxa sparusaurati infection was studied in gilthead sea bream from different mariculture systems of Spain. Culture conditions were found to influence the infection dynamics. Total prevalences ranged from 0 in a closed system to 59.9% in a Mediterranean semi-intensive farm. Prevalence was significantly lower in summer in a restricted group from the latter system, but no clear seasonal pattern was observed in the remaining fish groups in any system. A statistically significant dependence between infection prevalence and host weight was observed in some fish groups. Different degrees of histopathological damage were noted in the infected gallbladders, mainly involving swelling, vacuolization, and sloughing of the epithelial cells. Transmission electron microscope observations of the infected tissues demonstrated a characteristic protrusion of the epithelial cell surface and mitochondrial alterations. In fish from stocks showing external disease signs and trickling mortalities, parasite stages invaded other organs and were responsible for cell-mediated host reaction and important tissue injuries. Therefore, C. sparusaurati can be considered a potential threat for some Sparus aurata-growing systems. Received: 4 November 1996 / Accepted: 17 December 1996     

Ultrastructural and cytochemical studies on vitellogenesis in the trypanorhynch cestode <Emphasis Type="Italic">Parachristianella trygonis</Emphasis> Dollfus, 1946 (Eutetrarhynchidae)

During vitellogenesis in Parachristianella trygonis Trypanorhyncha, Eutetrarhynchidae) we distinguished four stages: (1) gonial or stem cell stage; (2) early differentiation stage concentrated on protein synthetic activity and shell-globule formation; (3) advanced differentiation stage with main cell activity concentrated on carbohydrate synthesis (glycogenesis) and massive glycogen storage in the form of α-glycogen rosettes and β-glycogen particles; and finally (4) mature vitellocyte stage. Early vitellocyte maturation is characterised by: (1) an increase in cell volume; (2) extensive development of large, parallel cisternae of GER that produce proteinaceous granules; (3) development of Golgi complexes engaged in packaging this material; (4) continuous enlargement of proteinaceous granules within vacuoles and their transformation into shell-globule clusters composed of heterogeneous material. Cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate for polysaccharides indicated a strongly positive reaction for the presence of α-glycogen rosettes and β-glycogen particles in the advanced stage of vitellocyte maturation. Both protein synthesis for shell-globule formation and carbohydrate synthesis or glycogenesis, important storage of nutritive reserves for the developing embryos, observed during cytodifferentiation of P. trygonis vitellocytes overlap in time to some extent. Mature vitelline cells are very rich in three types of cell inclusions accumulated in large amounts in their cytoplasm: (1) shell-globule clusters, playing an important role in egg-shell formation; (2) numerous large lipid droplets, as well as a high accumulation of lipid and α-glycogen rosettes and β-glycogen particles that undoubtedly represent important nutritive reserves for the developing embryos. Despite the fact that the type of vitellogenesis and ultrastructure of the mature vitellocyte in P. trygonis appears to differ to some extent from those of three other trypanorhynch species, its general pattern and ultrastructure greatly resembles those observed in other lower cestodes. Factors that may have contributed to the qualitative and quantitative variation in lipids during vitellogenesis among the four species of Trypanorhyncha, are identified and discussed.     

Ultrastructure of gamonts and gametes and fertilization ofSarcocystis sp. from the roe deer (Capreolus capreolus) in dogs

Gamonts ofSarcocystis sp. from the roe deer were examined in the intestine of dogs 10 h after inoculation. Early macrogamonts were limited by a three-membranous pellicle, and situated in a parasitophorous vacuole. Female sexual stages during fertilization, the macrogametes, were limited by five membranes, and microgametes were observed in the parasitophorous vacuole. The outer membranes of the microgamete and macrogamete fuse, and the nucleoplasm of the microgamete enters the cytoplasm of the macrogamete. No wall-forming bodies were observed in macrogamonts and macrogametes.     

Ultrastructural study of vitellogenesis in Maritrema feliui (Digenea, Microphallidae)

During vitellogenesis in the microphallid trematode Maritrema feliui, we distinguished four stages: (I) a stem cell stage of the gonial type; (II) an early differentiation stage with the main cell activity concentrated on the initiation of protein synthetic activity and the beginning of shell globule formation; (III) an advanced differentiation stage concentrated on a rapid intensification of protein synthetic activity, the progressive fusion of individual shell globules into large shell globule clusters and the formation of saturated lipid droplets and a small amount of β-glycogen particles in the peripheral cytoplasm, considered as a store of nutritive reserves for the developing embryos; and (IV) the mature vitellocyte. Early vitellocyte maturation is characterised by: (1) an increase in cell volume; (2) extensive development of large, labyrinth-like cisternae of GER that produce proteinaceous granules; (3) the development of Golgi complexes engaged in packaging this material; and (4) a continuous enlargement of proteinaceous granules within vacuoles and their transformation into shell globule clusters composed of the heterogeneous material observed during vitellocyte cytodifferentiation. Mature vitelline cells are very rich in two types of cell inclusions accumulated in large amounts in their cytoplasm: (1) shell globule clusters, which play an important role in eggshell formation; and (2) a few osmiophobic lipid droplets of a saturated nature that undoubtedly represent nutritive reserves for the developing embryos. In addition, there are small numbers of β-glycogen particles in the peripheral cytoplasm of mature vitellocytes of this species. The general pattern and ultrastructure of vitellogenesis in M. feliui greatly resembles those observed in another microphallid trematode, Maritrema linguilla, in other digeneans and in some lower cestodes. Quantitative and qualitative variations in lipids (saturated and unsaturated) and glycogen (α-glycogen rosettes and β-glycogen particles) during platyhelminth vitellogenesis between the different species of trematodes and some lower cestodes are identified and discussed.     

An electron microscopic and cytochemical study of the cell coat of Trypanosoma cruzi in tissue cultures

Summary Using the cytochemical method of Thiery, a polysaccharide surface coat was demonstrated with the electron microscope in the various developmental stages of Trypanosoma cruzi maintained in tissue cultures. The cell coat was observed on the whole surface membrane system of T. cruzi. A positive reaction, similar to that observed in the cell membrane, was also obtained in the membranes of some vacuoles in the cytoplasm of the parasites. No granules were found in the parasite which could represent reserve polysaccharides.The possible role of the cell coat in such phenomena as adhesion, agglutination, phago-and pinocytosis and antigenicity is discussed.This work has been partly supported by Conselho Nacional de Pesquisas, Conselho de Ensino para Graduados da Universidade Federal do Rio de Janeiro e Banco Nacional de Desenvolvimento Economico, contr. Funtec-241.     

Life-cycle of Isospora mehlhornii sp. nov. (Apicomplexa: Eimeriidae), parasite of the Egyptian swallow Hirundo rubicola savignii

Fifty-seven Hirundo rubicola savignii swallows were collected from Damietta, Tanta, Dakahlyia and Sharkia Provinces, Egypt. They were examined for coccidian parasites. The percentage of infection with Isospora stages was 12.3%. After diagnosis it was noted that the parasites belong to a new species. The unsporulated oocysts were spherical, measuring 25.7–31.9 μm in diameter with a mean of 28.3 μm. A micropyle, polar granule and oocyst residuum were absent. Sporocysts appeared lemon-shaped and measured 19.6–24.5 μm × 12.5–17.5 μm with a mean of 22.9 × 14.4 μm. Stieda body and the sporocyst's residual body were clearly visible. Sporozoites measured 11–14.2 × 4.4–5.1 μm with a mean of 11.4 × 4.7 μm. Sporulation time was 72 h at room temperature (25 °C). Endogenous stages including schizogony and gamogony were detected in epithelial cells of the duodenum, jejunum and ileum of the host. Schizogony consisted of two generations. Mature first generation schizonts reached up to 11 μm in diameter and produced merozoites measuring 3.5 × 1.7 μm. Mature second generation schizonts measured 17.2 × 12.3 μm and produced merozoites measuring 11.8 × 2.2 μm. Gamogonic stages were differentiated into microgamonts and macrogamonts. Mature microgamonts were spherical and measured 23.2 μm in diameter, producing curved microgametes measuring 4.5 × 0.7 μm. The ovoid macrogametes measured 19.6 × 14.7 μm and were characterized by a large nucleus and nucleolus. Early, more or less spherical, oocysts were detected inside the intestinal epithelial cells and in the intestinal lumen. They measured 19.6 μm in diameter. The sporont measured 17.2 μm in diameter. Cytochemical studies on schizogony, gamogony and oocysts were accomplished and showed distribution of polysaccharides and composition of the oocyst wall. Received: 15 May 1999 / Accepted: 25 June 1999     

Early organization of the pituitary gland in Sparus aurata L. (Teleostei) An ultrastructural study

The cell organization of the pituitary gland and the relationship between neurohypophysis and adenohypophysis in the early developmental stages of the gilthead sea bream, Sparus aurata, were studied by electron microscopy. In newly hatched larvae, the pituitary gland was embedded in the ventral floor of the diencephalon and separated from the hypothalamus by a continuous basal lamina. Elongated mesenchymal cells next to the ventral surface were observed. At this stage, there was no neurohypophysis and the adenohypophysis consisted of undifferentiated endocrine cells with small scarce secretory granules and a few stellate cells, with no distinctive zonation. An incipient neurohypophysis was present in 1-day-old larvae. The first evagination of the neurohypophysis into the adenohypophysis were observed in 2-day-old larvae and developed progressively with age, being deeper in the caudal zone. Two regions in the adenohypophysis, one anterior — the presumptive pars distalis — and one posterior — the presumptive pars intermedia — were found in 2-day-old larvae. Three regions (rostral and proximal pars distalis and pars intermedia) were clearly distinguishable in 4-day-old larvae. The ultrastructural features of the pituitary endocrine cells varied during gland differentiation, with the secretory granules gradually increasing in number and size, accompanying organelle development. Nevertheless, even in the oldest larvae studied (65 days), undifferentiated cells similar to those in the earliest stages were observed. The first blood vessels appeared in the neurohypophysis around 16 days after hatching. During early development, the pituitary gland progressively emerged from the ventral floor of the brain. By 16 days, the principal pattern of the pituitary gland architecture appeared to be established.     

Ultrastructural observations on the sexual stages and oocyst formation inEimeria laureleus (Protozoa,Coccidia) of perch,Perca flavescens,from Lake Sasajewun,Ontario

Ultrastructural features of the sexual stages and oocyst formation ofEimeria laureleus are described from the intestinal epithelium of naturally infected perch (Perca flavescens). Daughter nuclei in maturing microgamonts became aligned in the peripheral cytoplasm opposite thickenings in the limiting membrane. A pair of centrioles, originally arranged at right angles, transformed into basal bodies from which two axonemes arose during the formation of microgametes. Macrogamonts were bound by a trilaminar limiting membrane and were closely invested by the membrane of the parasitophorous vacuole. Maturing macrogamonts had a central nucleus, granular endoplasmic reticulum, amylopectin granules, lipid and peripherally arranged dense, membrane-bound inclusions and mitochondria. Spherical zygotes underwent two divisions to form the sporoblasts, each of which contained, in addition to the above mentioned organelles and inclusions, a large dense refractile body. Each of the four sporocysts contained two residual bodies and closely spaced tubular structures. Slender extensions arose from the sporocyst walls which were about 50 nm thick and were composed of a narrow lucent outer zone and a thicker inner, denser zone which is often striated. The sporocysts were bivalved and joined by a continuous suture. The oocyst boundary was multilaminate and appeared to be composed of components of both the parasite and host cell.     

In vivo and in vitro experimental intestinal amebiasis in Mongolian gerbils (Meriones unguiculatus )

  One of the main drawbacks of experimental amebiasis is the lack of an adequate animal model for invasive intestinal lesions. Mongolian gerbils are useful because both intestinal and hepatic amebiasis can be produced experimentally with Entamoeba histolytica trophozoites. In this paper we show results obtained with in vivo and in vitro models of intestinal amebiasis in gerbils. We inoculated gerbils intracecally with monoxenic cultures of a highly virulent E. histolytica HM1:IMSS substrain. In the in vivo model an increase in mucus production was observed during the first 6 h of interaction. Microulcerative mucosal lesions appeared at 24–72 h postinoculation. Inflammatory infiltrate and edema of the lamina propria were associated with superficial foci of necrosis. At 96 h the cecal mucosa had an almost normal appearance and live amebas were no longer detected. In the in vitro model, early damage was detected in cecal strips mounted in Ussing chambers as a rapid fall in potential difference, short-circuit current, and transepithelial resistance that correlated with the extent of the microscopic lesions produced. The latter consisted of cellular edema and the appearance of small, translucent vacuoles at the base of epithelial cells. Further damage led to loss of intercellular junctions, destruction of interglandular epithelial cells, and edema of the lamina propria. The present results demonstrate that the gerbil is useful as an experimental model for the analysis of early stages of invasive intestinal amebiasis both in vivo and in vitro. Received: 5 April 1996 / Accepted: 21 August 1996     

The fine structure of the endogenous stages ofEimeria labbeana

Summary The fine structure of the microgamonts and microgametes ofEimeria labbeana from the columnar epithelial cells of the ileal mucosa of experimentally infected pigeons,Columba livia, has been described and compared with that of similar stages in other species ofEimeria. The microgamonts averaged 8.0×10.0 μm (6.7–8.4×9.0–11.4 μm), had a maximum number of 27 nuclei each (0.8–1.0×1.0–1.3 μm), and showed various stages of mitotic nuclear divisions without the appearance of detectable mitotic spindles. Modification of the membrane of some of the nuclei into spirally coiled structures containing granular bodies resembling autophagosomes were observed. One pair, and occasionally two pairs of centrioles with the typical (9+1) microtubular composition were seen in association with some of the nuclei. Polysaccharide granules were seen in only about 5% of the more than 2,000 microgramonts studied. Cytomere formation was not observed but development of microgametes in association with intra-cytoplasmic spaces, and surface invaginations was frequently seen. Microgametes were elongate to slightly curved, averaged 3.1×1.2 μm (2.8–3.3×0.8–1.3 μm), and each was composed of an apical perforatorium, 2 basal bodies, 2 flagella, 4 microtubules representing a third but rudimentary flagellum, a row of more than 15 short microtubules located laterally in the apical region, a large nucleus (1.7×0.8 μm), and a mitochondrion. Subfibrillar composition of the basal body and basal-plate region was observed. The microgametes ofE. labbeana are the shortest and stoutest ever reported from the genusEimeria. The maximum number of microgametes detected from any one section was thirty.     

Morphological, cytochemical, and ultrastructural observations on the blood cells of the reptile Tupinambis merianae (Squamata)

Tupinambis merianae is a lizard of the Brazilian fauna and belongs to the Squamata order. Blood cell data are scarce. Blood samples from six specimens of adult T. merianae were used to evaluate some hematological parameters. For structural analysis, 2 ml of blood was collected in the presence of EDTA. Part of the blood was used for preparing blood smears which were submitted to the methods of Leishman, Laür, and toluidine blue, and the cytochemical reactions of periodic acid-Schiff, sirius red, sudan black B, and ortho-toluidine-H₂O₂. The remainder was centrifuged and the leukocyte buffy coat was fixed in Karnovsky’s fluid for electron microscopy examination. The following blood cells were identified: mature and immature erythrocytes, spherical and elliptical thrombocytes, heterophilic granulocytes, eosinophils and basophils types I and II, lymphocytes, monocytes, and azurophilic cells. The more significant results obtained were: the presence of glycogen in the cytoplasm of the thrombocytes, heterophils, and basophils; the presence of basic polyaminoacid-rich proteins in the granules of heterophils and eosinophils and myeloperoxidase in the granules of the heterophils, eosinophils, and azurophilic cells; and sudanophilic small granules in the heterophils, eosinophils, and azurophilic cells. More detailed morphological aspects of the cells were observed by means of ultrastructural analysis.     

Frontal glands in the pseudoscolex of <Emphasis Type="Italic">Paraechinophallus japonicus</Emphasis> (Yamaguti, 1934) (Cestoda,Bothriocephalidea, Echinophallidae)

The glands in the pseudoscolex of the echinophallid cestode Paraechinophallus japonicus (Bothriocephalidea), a parasite of the bathypelagic fish Psenopsis anomala (Perciformes, Centrolophidae), were studied using scanning and transmission electron microscopy. Two types of glands, with different morphological types of secretory granules and mechanisms for discharging their glandular secretion, were observed. Both types of gland cell bodies are localized in the parenchyma of the pseudoscolex. The syncytial glands of type I are characterized by the production of small (all ∼0.25 μm in diameter), rounded, dense secretory granules which pass though thin projections into the distal tegumental layer of the pseudoscolex. This type of gland has a unique method of discharging its secretory granules, which we call tumulogenesis. The elimination of the secretory products is realized by an encroachment of the basement membrane and underlying tegumental muscles into the surface region of the distal cytoplasm of the tegument, resulting in the formation of a ‘glandular stalk’ above which develops a superficial glandular tumulus. In the region of the glandular material of the tumulus, the basement membrane of the stalk forms a dilation, and the appearance of a membrane-bound area serves to separate the tumulus from the distal cytoplasm of the tegument. Unicellular glands of type II are characterized by large granules (0.4–0.9 μm in diameter), the presence of peripheral microtubules in the terminal region of their ducts and an eccrine mechanism for the discharge of their secretory granules. A comparative analysis of the distribution and morphology of the types of scolex glands among members of the different families of the ‘Pseudophyllidea’ (currently believed to represent two distinct orders, Bothriocephalidea and Diphyllobothriidea) is presented.     

Composition of glycoproteins of the supraepithelial mucous layer of the intestinal tract for administration of pentagastrin and carbacholine

The composition of structural glycoproteins from the supraepithelial mucous layer of the stomach and intestine was determined by the concentration of the protein part and monosaccharides of the oligosaccharide part in dogs. It is shown that after administration of pentagastrin at 10 μg/kg and carbacholine at 6 μg/kg the release of structural glycoproteins increases in the stomach (the degree of glycosylation as well as the partial composition of monosaccharides does not markedly change). After stimulation of gastric secretion, the release of structural glycoproteins in the intestine increases insignificantly, whereas the glycosylation of glycoproteins from the supraepithelial mucous layer of the stomach is intensified. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 118, N ^o 9, 237–240, September, 1994     

Amplification of genomic DNA fragments of Sarcocystis muris (Apicomplexa) cyst merozoites encoding a thiol (cysteine) proteinase

Parasites of the phylum Apicomplexa (Sporozoa) cause diseases such as malaria, toxoplasmosis, or intestinal coccidiosis. Invasive stages possess typical apical organelles such as dense granules that harbor a broad range of polypeptides that are believed to take part in the parasite-host cell interaction. In previous studies a 26-kDa polypeptide of dense granules from Sarcocystis muris cyst merozoites (bradyzoites) was characterized as a thiol (cysteine) proteinase. In this paper a method is demonstrated to amplify DNA fragments from genomic DNA of S. muris cyst merozoites by polymerase chain reaction, which probably code for the 26-kDa antigen. Received: 12 December 1997 / Accepted: 17 January 1998     

Immunohistochemical characterization of a polyclonal antibody against Sphaerospora dicentrarchi (Myxosporea: Bivalvulida), a parasite from sea bass (Dicentrarchus labrax L.) (Teleostei: Serranidae)

Rabbit antibody was raised against Sphaerospora dicentrarchi, a histozoic parasite of sea bass (Dicentrarchus labrax L.). Light and electron immunohistological staining were used to characterize its specificity and possible reactivity toward other fish parasites. In light immunohistochemistry the polar capsules and valves of the S. dicentrarchi spores appeared strongly stained, whereas developmental stages were not. Electron microscopic histochemistry revealed intense labeling in valves and some developmental stages. Cross-reaction was observed with all the myxosporean parasites assayed, even with those belonging to other genera. Polar capsules of all the myxosporean species except Polysporoplasma sparis were the main structures stained by the polyclonal antibody. These observations could reveal the existence of conserved antigenic epitopes in polar capsules of different Myxosporea. Received: 17 April 1998 / Accepted: 13 May 1998