The spermatozoon morphology of Solea senegalensis (Kaup, 1858) (Teleostei, Pleuronectiformes)

The spermatozoon of Solea senegalensis (Kaup, 1858) consists of an acrosome-less ovoid head, a short midpiece containing several irregular mitochondria embedded in the cytoplamic mass, and a long tail with two lateral fins and a conventional 9 + 2 axoneme. The centrioles are housed in a deep nuclear fossa and are both orientated in the same longitudinal axis of the spermatozoon. The overall structure of this spermatozoon conforms to the sperm type considered to be plesiomorphic in the neopterigians (type I sperm). The likely apomorphic (coaxial) orientation of the centrioles defines the spermatozoal morphology of the Soleidae investigated thus far and separates them from the other known pleuronectiform spermatozoa.     

Ultrastructure of spermiogenesis and the spermatozoon of Opecoeloides furcatus (Trematoda, Digenea, Opecoelidae), a parasite of Mullus barbatus (Pisces, Teleostei)

Spermiogenesis and mature spermatozoa of Opecoeloides furcatus (Digenea, Opecoelidae) are described by means of transmission electron microscopy. Spermiogenesis in this fluke matches the general pattern of digenetic trematodes. Striated rootlets associated with the two centrioles and an intercentriolar body are present in the differentiation zone. Flagellar rotation of two flagella and their proximodistal fusion with a median cytoplasmic process also characterize the spermiogenesis of O. furcatus. Nevertheless, asynchronicity is reported for the proximodistal fusion of the two flagella. Mature spermatozoa of O. furcatus are filiform, tapering at both ends and they present all the characteristic features found in the Digenea gamete: two flagella, mitochondrion, nucleus and two bundles of parallel cortical microtubules. Nevertheless several peculiarities distinguish the mature spermatozoon of O. furcatus from the gamete of other digenetic trematodes. Received: 19 August 1999 / Accepted: 1 October 1999     

Ultrastructure of spermiogenesis and mature spermatozoon of Skrjabinoporus merops (Cyclophyllidea, Metadilepididae)

The ultrastructure of the mature spermatozoon and the spermiogenesis of a cestode belonging to the family Metadilepididae is described for the first time. The mature spermatozoon of Skrjabinoporus merops is characterized by twisted peripheral microtubules, the presence of a single crested body, periaxonemal sheath and electron-dense rods, and the absence of intracytoplasmic walls and inclusions (glycogen or proteinaceous granules); no peripheral microtubules where nucleus contacts the external plasma membrane. Four morphologically distinct regions of the mature spermatozoon are differentiated. The proximal part (Region I) contains a single crested body, periaxonemal sheath is absent in some (proximal) sections and is present in others situated closer to the nucleus. The central Region II is nucleated, and is followed by Region III that contains a periaxonemal sheath. The distal pole, Region IV, is characterized by disintegration of the axoneme. Spermiogenesis follows the type III pattern (Ba and Marchand 1995) although in S. merops a slight flagellar rotation is observed. The differentiation zone is characterized by the absence of striated roots and intercentriolar body; two centrioles are present, one of which gives rise to a free flagellum. The latter rotates and undergoes proximodistal fusion with the cytoplasmic protrusion of the differentiation zone. Spermiological characters of S. merops are similar to those of the families Taeniidae and Catenotaeniidae. The mature spermatozoon differs from those of the Dilepididae (where the metadilepidid species have previously been classified) by the lack of glycogen.     

Topography and ultrastructure of the tegument of Deropristis inflata Molin, 1859 (Digenea: Deropristidae), a parasite of the European eel Anguilla anguilla (Osteichthyes: Anguillidae)

The tegumental ultrastructure of the intestine fluke Deropristis inflata was studied using scanning and transmission electron microscopy. The surface of the tegument was covered by transverse cytoplasmic ridges from which protrude numerous thorn-like spines showing crenelated tips on the posterior part. Spines were arranged in staggered rows. Cobblestone-like units of the tegument were observed on a semicircle-shaped formation over the oral sucker. A tegumental excrescence was observed in the dorsal anterior side of the fluke. Ultrastructural study revealed that the tegument of D. inflata had a typical syncytial organization with a distal cytoplasm lying over a basal matrix and cytons. Cytoplasmic bridges allowed transit of secretory vesicles and granules packed in gland cells. Two types of sensory structures were examined. Type 1 sensory receptor was a button-like uniciliated papilla mounted on a folded tegumental base and surrounded by cytoplasmic ridges. This receptor consisted of a nerve bulb and a cilium that extended from a centriole. Type 2 sensory receptor was a smooth bulb-like non-ciliated papilla. It was only recovered on the ventral sucker. This receptor consisted of a nerve bulb enclosing an ovoid electron-dense structure. For both receptors, the nerve bulbs contained numerous mitochondria, nerve fibers, and electron-lucent material. Particular distributions of the sensory receptors were observed with a concentration on the anterior third of the body around the oral and ventral suckers. Diagrams were made to help in understanding the nature of these structures.     

Affinity Purification of Antigen-Specific Serum Immunoglobulin from the European Eel (Anguilla anguilla)

Immunization of specimens of the European eel with a hapten-carrier conjugate resulted in a significant rise in anti-hapten titres. Antigen-specific immunoglobulin was purified on a matrix onto which the hapten-carrier conjugate had been immobilized. Rabbit antisera raised against the product of the affinity purification recognized two molecular moieties. The first was eel immunoglobulin as inferred by the polypeptide composition, i.e. disulphide-linked heavy and light chains of 72 kDa and 25 kDa respectively. The second was a 110-kDa protein. A 800-kDa and a 400-kDa molecular form of eel immunoglobulin were disclosed by a combination of gel filtration and immunoelectrophoretic detection. The latter was the more abundant serum form. The 110-kDa protein was found non-covalently associated with the 400-kDa immunoglobulin. Both molecular forms of immunoglobulin from immune sera exhibited antigenic specificity and reactivity.     

The spermatozoon of the Chinese bitterling, Rhodeus sericeus sinensis (Cyprinidae, Teleostei)

The bitterling spermatozoon has been examined by electron microscopy using sectioned material and freeze-fracture replicas. Its structure is characterized by a higher degree of order than is seen in spermatozoa of related teleosts. The intramembrane particles in the cell membrane are arranged in a large (around 1 micron in diameter) hexagonal grating pattern at a certain site of the sperm head. The flagellum protrudes from a site slightly posteriorly to this hexagonal grating and is surrounded by a cytoplasmic sleeve that contains regularly spaced filaments in a helical arrangement. The sperm midpiece contains a large mitochondrion enclosed in an elaborate system of membranous cisternae and narrow tubules. Fertilization in the bitterling takes place in the gill chamber of freshwater mussels--a unique brood chamber and site of fertilization for a vertebrate.     

Sparicotyle chrysophrii (Van Beneden and Hesse 1863) (Monogenea: Polyopisthocotylea) parasite of cultured Gilthead sea bream Sparus aurata (Linnaeus 1758) (Pisces: Teleostei) from Corsica: ecological and morphological study

Sparicotyle chrysophrii infections were highlighted during a parasitological monitoring carried out on cultured Gilthead sea bream Sparus aurata Linnaeus 1758 from aquaculture sites in Corsica. Factors and biological mechanisms regulating parasites populations, particularly controlling the infestation and survival of monogeneans have been studied. Variations in infection support the hypotheses that the main factor determining the infection of S. chrysophrii was temperature and that the parasite life cycle could be influenced by fish size and fish age. One hundred forty-nine of 280 S. aurata studied were infected. Seasonal differences in prevalence of infection were observed in all farms studied. A similar pattern was observed for parasite abundance with maximal infection levels occurring when water temperature were lower. A statistically significant dependence between infection and host size was also observed. The study of the surface topography of S. chrysophrii with scanning electron microscopy highlighted morphological adaptations not previously described. Parasites have developed diverse mechanisms of survival within the host that facilitate the establishment of infection. We mainly studied sensory structures and the anchoring systems of the parasite, i.e., filaments of eggs and haptor, enabling it to ensure the dispersal and survival of the species.     

Ultrastructure of spermiogenesis and mature spermatozoon of Angularella beema (Clerc, 1906) (Cestoda, Cyclophyllidea, Dilepididae)

The ultrastructure of the spermiogenesis of a dilepidid cestode species is described for the first time. The spermiogenesis of Angularella beema is characterised by absence of both flagellar rotation and proximodistal fusion. The differentiation zone is surrounded by cortical microtubules and is delimited by a ring of arching membranes. It contains two centrioles, one of which develops the axoneme that grows directly into the elongating cytoplasmic protrusion. This pattern of spermiogenesis was described as the Type IV spermiogenesis of cestodes. Among cestodes, similar pattern of spermiogenesis is known in the family Hymenolepididae and in some representatives of the family Anoplocephalidae. The mature spermatozoon of A. beema consists of five regions differing in their ultrastructural characteristics. It is characterised by the presence of cortical microtubules (spirally arranged at angle of 30–40° to the spermatozoon axis) and a single crested body. There is a periaxonemal sheath in certain parts of the spermatozoon as well as glycogen-like granules between the periaxonemal sheath and the cortical microtubules. The comparisons of the mature spermatozoon of A. beema with those of other two dilepidid species (Dilepis undula and Molluscotaenia crassiscolex) demonstrate some variation within the family: presence of periaxonemal sheath in A. beema and D. undula and its absence in M. crassiscolex; presence of electron-dense rods in D. undula and their absence in A. beema.     

Ultrastructural features of the spermatozoon and its differentiation in Brandesia turgida (Brandes, 1888) (Digenea,Microphalloidea, Pleurogenidae)

Spermatological characters of the digenean Brandesia turgida (Brandes, 1888), an intestinal parasite of the frog Pelophylax ridibundus (Pallas, 1771), have been investigated by means of transmission electron microscopy for the first time. The process of the spermatozoon formation begins with the appearance of the differentiation zone bordered by cortical microtubules and containing two centrioles associated with striated rootlets and with an intercentriolar body. The intercentriolar body is made up of seven distinct electron-dense plates, two less electron-dense, and four electron-lucent zones. The orthogonal development of the two flagella is followed by a flagellar rotation and their proximodistal fusion with the median cytoplasmic process. This process is accompanied by an extension of both the mitochondrion and nucleus into the median cytoplasmic process. The mature spermatozoon of B. turgida contains two parallel axonemes of unequal lengths with the 9?+?“1” trepaxonematan pattern, mitochondrion, nucleus, parallel cortical microtubules, four electron-dense attachment zones, an external ornamentation of the plasma membrane, and electron-dense glycogen granules. The anterior extremity of the male gamete contains one complete centriole, a small component of the central element of the second centriole, and peripheral cortical microtubules (up to 45). The posterior extremity of the mature spematozoon exhibits tubular elements of the disorganized axoneme. The present study provides the first data on spermiogenesis within the family Pleurogenidae. Variations of the spermatozoa ultrastructural characters within Digenea, in particular, between different families of the superfamily Microphalloidea, are discussed.     

Ultrastructural study of the spermatozoon of <Emphasis Type="Italic">Nicolla testiobliquum</Emphasis> (Digenea,Opecoelidae) parasite of brown trout <Emphasis Type="Italic">Salmo trutta</Emphasis> (Pisces,Teleostei)

The present paper describes the spermatozoon of Nicolla testiobliquum (Digenea, Opecoelidae), an intestinal parasite of brown trout Salmo trutta, studied by transmission electron microscopy. The mature spermatozoon possess two axonemes of 9 + “1” pattern, two mitochondria, a nucleus, external ornamentation of the plasma membrane, spine-like bodies and cortical microtubules. A comparative study between N. testiobliquum and Nicolla wisniewskii shows mainly two different dispositions of the two mitochondria in these two species of a same genera. Moreover, the comparison of each of these spermatozoon features with others digeneans, in general, and other Opecoelidae in particular, is also presented. It appears that the organisation of the posterior part of the spermatozoon, the disposition of cortical microtubules and external ornamentation associated with spine-like bodies could be interesting elements for phylogeny.     

Ultrastructure of spermiogenesis and the spermatozoon of<Emphasis Type="Italic"> Monorchis parvus</Emphasis> Looss, 1902 (Digenea,Monorchiidae), a parasite of<Emphasis Type="Italic"> Diplodus annularis</Emphasis> (Pisces,Teleostei)

The present paper describes the characteristic ultrastructural features of spermiogenesis and the spermatozoon of Monorchis parvus (Trematoda, Digenea, Monorchiidae). This spermiogenesis is characterized by a flagellar rotation of about 120° and the formation of a novel ultrastructural element: a centriolar extension. It nevertheless follows the general pattern of digeneans. It begins with the formation of a differentiation zone, comprising striated rootlets associated with two centrioles and an intercentriolar body. The mature spermatozoon presents features allowing the distinction between M. parvus and other digenetic trematodes. It possesses an original anterior extremity. The two central elements of the axonemes appear prior to the peripheral doublets. The external ornamentations of the cell membrane are formed parallel to the central elements. Another peculiarity of the male gamete is the presence of two mitochondria. M. parvus, therefore, differs distinctly from other digenetic trematodes.     

Light and electron microscopy of the bulbus arteriosus of the European eel (Anguilla anguilla)

The bulbus arteriosus of teleost fish acts as an elastic reservoir that dilates during ventricular systole to store a large part of the cardiac stroke volume. Despite its functional importance, the knowledge of the structure of the bulbus wall is still fragmentary. We have undertaken a series of studies in order to establish a general morphological plan of the teleost bulbus. The bulbus arteriosus of the European eel is studied here by means of conventional light, and transmission and scanning electron microscopy. The inner surface of the bulbus wall is irregular due to the presence of branching ridges that flatten and disappear toward the ventral aorta. The ridge surface is covered by flattened endocardial cells that show moderately dense bodies. In the ridge tissue, cells near the endocardium are mostly undifferentiated and appear isolated in a loose filamentous matrix. Ridge cells progressively cluster toward the middle layer, become surrounded by a dense matrix, and adopt characteristics typical of smooth muscle cells. This suggests the existence of a differentiation gradient. The middle layer is formed by typical smooth muscle cells embedded in a meshwork matrix that contains thin and thick filaments. Stretching of this meshwork suggests an active role of smooth muscle cells in bulbus wall dynamics. Furthermore, large areas of the extracellular space are occupied by elastin-like material. The amount of this material decreases toward the external layer. Collagen is demonstrated across the entire thickness of the bulbus wall, its amount and organization increasing from the inner toward the outer bulbus surface. The existence of matrix gradients should progressively increase wall strength, maintaining bulbus dilation within safe physiological parameters. The epicardium is formed by flattened cells that contain numerous pinocytotic vesicles, suggesting an active interchange of solutes with the pericardial cavity.     

Ultrastructure of spermiogenesis and the spermatozoon of Sudarikovina taterae (Cestoda, Cyclophyllidea, Anoplocephalidae) intestinal parasite of Tatera gambiana (Rodentia, Gerbillidae)

The young spermatid of Sudarikovina taterae exhibits a nucleus with a partially condensed chromatin and a differentiation zone, bordered by cortical microtubules, delimited at the front by arched membranes and containing two centrioles. The latter are parallel to one another and linked together at their bases by electron-dense material. During spermiogenesis, one of the centrioles gives rise to a flagellum whereas the other disappears. Crested-like bodies lie outside the cortical microtubules and the nucleus migrates in the spermatid along the axoneme. At the end of spermiogenesis, the ring of arched membranes constricts and the old spermatid becomes detached from the residual cytoplasm. The S. taterae mature spermatozoon is filiform and tapered at both extremities. It exhibits an apical cone of electron-dense material and seven crested-like bodies 50 to 100 nm thick. The cortical microtubules run along the whole length of the spermatozoon. They are spiralized at their anterior extremities and straight over the rest of their length. The nucleus is a fine compact cord interposed between the axoneme and the cortical microtubules. The cytoplasm is slightly electron-dense in regions I and II of the gamete. In regions III, IV and V, it contains fine electron-dense granulations and patches of electron-lucent material. An electron-dense material located both between and under centrioles has not been observed before in a platyhelminth. Similarly, distinctive ultrastructural characters between centrioles and seven crested-like bodies have not been previously described in a cestode. Moreover, we report for the first time the existence of cortical microtubules spiralized only at their anterior extremities in a cestode from a mammal.     

Demonstration of the orientation of the Cestodes spermatozoon illustrated by the ultrastructural study of spermiogenesis and the spermatozoon of a Cyclophyllidea: Thysaniezia ovilla, Rivolta, 1874.

Spermiogenesis in Thysaniezia ovilla begins with the appearance of a differentiation zone equipped with peripheral microtubules, surrounded by arched membranes and containing two parallel centrioles surrounded by electron dense granular material. One of the centrioles aborts, the other gives rise to a flagellum which quickly grows in the cytoplasmic extension in which the nucleus migrates and protein granules form. During the nuclear migration crested-like bodies appear among the peripheral microtubules in the differentiation zone. The Th. ovilla spermatozoon is filiform. One of its extremities, which we show to be anterior, exhibits two helicoidal crested-like bodies, surrounded by electron dense material resembling an acrosome. Cortical microtubules run along almost the whole length of the spermatozoon. The cytoplasm has no mitochondria and contains protein granules. The axoneme is of the 9 + '1' pattern. It stops before reaching the posterior extremity of the gamete. The nucleus is wrapped round the axoneme, in the middle region of the spermatozoon. It generally stops before reaching the posterior extremity of the flagellum. This study has enabled us to describe precisely the orientation of the spermatozoon of cestodes in general.     

Localization of carbonic anhydrase in swimbladder of European eel (Anguilla anguilla) and perch (Perca fluviatilis)

The distribution of carbonic anhydrase in swimbladder tissue and especially in gas gland cells of the European eel (Anguilla anguilla) and the perch (Perca fluviatilis) was analysed using histochemical staining according to Hansson (1967), with modifications proposed by Ridderstr?le (1991). While in the European eel, gas gland cells are distributed as a single layered epithelium over the whole secretory part of the swimbladder, the gas gland of the perch consists of a compact, richly vascularized 'multilayered' epithelium, in which gas gland cells have contact with the swimbladder lumen via small channels. In spite of these differences in organization, membranes of gas gland cells near blood vessels are richly folded in both species. A strong histochemical staining for carbonic anhydrase was observed in these membrane foldings. With prolonged incubation times a positive reaction was also observed in the cytoplasm of gas gland cells. In addition, the vascular endothelium and the erythrocytes showed a positive histochemical reaction. No staining, however, was visible in apical membranes towards the lumen of the swimbladder. In the perch, swimbladder epithelial cells outside the gas gland showed no positive staining of carbonic anhydrase. The results thus indicate that carbonic anhydrase activity is especially concentrated in membranes facing blood vessels. This suggests that a rapid equilibrium of the CO2/HCO3- reaction in the intracellular as well as in the extracellular space is essential for swimbladder function.     

Ultrastructural studies of the spermatogenesis and spermiogenesis of the caryophyllidean cestode Wenyonia virilis (Woodland, 1923)

Spermatogenesis and spermiogenesis of the monozoic caryophyllidean cestode Wenyonia virilis (Woodland, 1923), an intestinal parasite of Synodontis schall (Pisces: Siluridae), have been investigated by means of transmission electron microscopy for the first time in Egypt. Spermatogenesis is of a rosette type; each spermatogonium undergoes four mitotic and two meiotic divisions resulting in the formation of sixty four spermatids. These spermatids undergo spermiogenesis and transform into mature spermatozoa. The process of spermiogenesis begins by the formation of the zone of differentiation, at one end of the spermatid cell, with one pair of centriole but without an intercentriolar body. The left-handed centriole, firstly, forms a basal body but aborts forming a flagellar bud. The right-handed one develops externally into an axoneme growing parallel to a cytoplasmic extension protruding from the differentiating zone. The nucleus penetrates this extension followed by the proximodistal fusion of the axoneme in the sperm shaft. The spermatozoon of W. virilis lacks mitochondria and consists of five regions showing gradual increase in the nucleus width and the presence of glycogen granules. Some important differences between the present study and others done on monozoic and polyzoic worms are recorded and discussed.     

Site influence in parasite distribution from fishes of the Bonifacio Strait Marine Reserve (Corsica Island,Mediterranean Sea)

The spatial distribution of parasite communities from teleost fishes (Diplodus vulgaris, Mullus surmuletus, Pagellus erythrinus, Phycis phycis, Scorpaena scrofa and Symphodus tinca) was studied in the Bonifacio Strait Marine Reserve (Corsica Island) with different protection levels. Canonical correspondence analysis was used to study spatial patterns and to quantify the importance of site influence on parasite communities. To supplement these results, we used the indicator species analysis (Indval) to identify parasite species as bioindicators of a given ecosystem. Moreover, fish spatial distribution in the marine reserve was evaluated in order to link parasite species occurrence and fish abundance. Several parasite species were associated with a specific site, and some of them were considered as site bioindicators, especially in the western part of the protected area (Bruzzi and Moines Islands). However, the relative abundance of fish followed a different spatial pattern. Stronger fish abundance was observed in the eastern part of the reserve (Lavezzi Islands). The parasite species were correlated to sites inside as well outside the reserve. The parasite distribution seemed not to be influenced by the protection status of the site. Furthermore, in our study, most of the parasite species were not linked to a site. The most important factor influencing their distribution was host specificity. This suggested that the parasite life traits history remained a fundamental determinant in the community composition.