Light and transmission electron microscopy of the haptoral sclerites of the monogenean gill parasite Macrogyrodactylus clarii.

The present study represents the first detailed description of the haptoral sclerites of Macrogyrodactylus clarii Gussev 1961. Light microscopy reveals outgrowths of the hamuli roots; two lateral spine-like extensions of the hood-like accessory sclerites; a ridged, fan-shaped distal end of an accessory sclerite; and two thread-like accessory sclerites with biforked ends associated with the pointed hooked region of each hamulus. Transmission electron microscopy (TEM) reveals the presence of parallel tubules in the root of the hamuli and structural differences along the length of the hamulus including the root, shaft, and pointed hooked region. The root consists of two layers, the shaft four layers and pointed hooked region only one layer with dense outer serrations. Characteristic features of the hamulus root are the presence of longitudinally orientated parallel tubules in its central core and parallel electron-dense ridges in the outer layer of its middle region; features not observed in either the shaft or the pointed hooked region. Each hamulus blade of M. clarii is associated with haptoral gland cells producing electron-dense secretory bodies. The 16 marginal hooklets each consist of a blade (sickle) articulating with a handle at the guard region and a domus. TEM revealed structural differences between the handle, the blade at the articulation region, and the distal hooked region. The domus, a filamentous thread-like sclerite at the light microscope level, consists of two electron-dense, fibrous thickenings connected to each other by a cytoplasmic process. Each marginal hooklet is associated with a small cavity and a large reservoir of homogeneous particles and secretory bodies. The possible functions of these structures are discussed in relation to equivalent features in other monogeneans.

Ultrastructure of the anterior adhesive apparatus of the gill parasite Macrogyrodactylus clarii and skin parasite M. congolensis (Monogenea; Gyrodactylidae) from the catfish Clarias gariepinus.

Transmission electron microscopy (TEM) was used for the first time to study the anterior adhesive apparatus of the monogeneans Macrogyrodactylus clarii Gussev, 1961 and M. congolensis (Prudhoe, 1957) Yamaguti, 1963 inhabiting gills and skin respectively of the same catfish Clarias gariepinus. Despite the different microhabitats occupied by these parasites, the present study revealed that they have a similar anterior adhesive system. In both parasites, the anterior adhesive apparatus consists of three types of gland cells: G1 cells that produce rod-shaped bodies (S1), G2 cells manufacture irregularly shaped bodies (S2) and G3 cells form mucoid-like secretions (S3). In the cytoplasm of G1 cells, a single layer of microtubules encloses each developing rod-shaped body. A unique feature of S1 secretory bodies is that some fully developed S1 bodies are attached to each other, forming large condensed globules in the cytoplasm of G1 gland cells and terminal portion of the G1 ducts, but none were detected in the adhesive sacs outside the ducts. In the adhesive sacs, G1 ducts open with multiple apertures whereas each of the G2 and G3 ducts have a single opening. The adhesive sacs are lined with two types of tegument (st1 and st2). A third tegument type (st3) connects the st2 tegument with the general body tegument. Only st1 has microvilli. Each adhesive sac is provided with a spike-like sensillum and single uniciliated sense organ. The possible functions of microvilli in increasing the surface area and assistance in spreading and mixing of the adhesive secretion, and the role of sense organs associated with the adhesive sacs are discussed.

Scanning and transmission electron microscopy of the histopathological impact of Macrogyrodactylus clarii (Monogenea: Gyrodactylidae) on the gills of catfish, Clarias gariepinus.

Scanning and transmission electron microscopy (TEM) were used to study the histopathological effects of the monogenean Macrogyrodactylus clarii Gussev, 1961 on the gills of the catfish Clarias gariepinus (Burchell). Suction generated during attachment created 'footprints' on host surfaces in which the host tissues were elevated above the general gill surface. 'Footprints' were bordered by four clefts caused by the muscular flaps on the anterior, lateral and posterior margins of the haptor. The hamuli points penetrate the gill tissue but no evidence was found for the insertion of the marginal hooklets. At the site of attachment, host cells adjacent to the lateral flaps often appeared compressed and widely spaced with large intercellular spaces. Desquamation of these surface epithelia was also apparent and some of the widely spaced epithelial cells had pseudopodium-like processes. Cells within the upper surface epithelial layer of the host were vacuolated and necrotic. Ruptured blood capillaries (blood spaces) in the secondary gill lamellae contained atypical compressed erythrocytes, agranular and granular leucocytes and evidence of haemorrhaging. Cells with fibrotic cytoplasm, putative phagocytes and host mucous cells were evidence of a host response at the site of parasite attachment. The possible role of these cells is discussed in relation to host resistance against infection.

Histochemical demonstration of five enzymes' activities in Macrogyrodactylus clarii (Monogenea: Gyrodactylidae) from the catfish Clarias gariepinus.

Histochemical techniques were applied to whole mounts, to study the distribution of the enzymes alkaline phosphatase, acid phosphatase, adenosine triphosphatase, 5'-nucleotidase and glucose-6-phosphatase in the organs and tissues of a viviparous monogenean, Macrogyrodactylus clarii Gussev, 1961, from the gills of the North African catfish Clarias gariepinus (Burchell) in Egypt. The following organs and tissues were studied: head region, anterior adhesive glands, mouth region, pharynx, intestine, testis, vesicula seminalis, male accessory gland, male accessory reservoir, copulatory organ, receptaculum seminis, egg-cell forming region, embryonic cells, excretory system, nerve cells, haptor, muscle fibres and subtegumental cell bodies (cytons). The enzymes showed marked differences in their activities among the studied organs and tissues. Alkaline phosphatase and acid phosphatase activities were detected in many organs and tissues, while the activities of adenosine triphosphatase, 5'-nucleotidase and glucose-6-phosphatase were restricted to a few organs. Although no positive reaction for any enzyme was observed in the anterior adhesive gland cells, a positive reaction for acid phosphatase was detected in the anterior adhesive areas. All enzymes showed marked activity in the digestive and excretory systems. The distribution of the enzymes in the tissues and organs of M clarii is compared with those of other monogeneans, including other gyrodactylids parasitizing the same host fish. Some possible functions of the enzymes are discussed.