On some ultrastructural features of the reproductive system of the monogenean parasite Macrogyrodactylus congolensis from Clarias gariepinus inhabiting the River Nile in Egypt

Some organs of the reproductive system of the protogynous monogenean skin parasite Macrogyrodactylus congolensis (Prudhoe, 1957) Yamaguti, 1963 have been studied using transmission electron microscopy. The vesicula seminalis is enclosed by a prominent layer of circular muscle fibres and has inner syncytial protrusions. The penis bulb is a highly muscular organ with prominent radial and circular muscle fibres, a gutter-shaped large spine and 16 small spines. Two syncytial male accessory glands, and a single reservoir for male accessory secretion were identified. The secretory bodies in the male accessory glands and male accessory reservoir have a unique structure. A large oocyte is situated in a chamber, previously referred to as the “ootype” or “egg-cell-forming region” (ECFR), which also contains one or two small undifferentiated cells and vacuolated tissue. Mature spermatozoa were abundant in the receptaculum seminis and dispersed in the vacuolated tissue in the ECFR and appeared to be attached to the membrane of the large oocyte. Mature spermatozoa were also seen in the parenchymal tissue near the chamber containing embryos and even in the tissues of the embryo.

Ultrastructure of the digestive system and experimental study of feeding in the monogenean skin and fin parasite Macrogyrodactylus congolensis

In the present study, transmission electron microscopy (TEM) has been used to study the ultrastructure of the digestive system, namely the pharynx, oesophageal glands and intestine, of the monogenean skin and fin parasite Macrogyrodactylus congolensis. The pharynx consists of an anterior highly muscular region and a posterior mainly glandular syncytial region. The anterior region is provided with six pharyngeal papillae, the centre of each of which is occupied by electron dense secretory bodies, identical with those in the posterior region of the pharynx. The intestine has an uninterrupted syncytial gastrodermis and the luminal surface is provided with many unbranched lamellae. The intestine of living specimens contains large and small granules which give it a reddish brown colour. Large particles, presumed to be lipid droplets, and small granules, presumed to be melanin granules, were found in the gastrodermis and in the intestinal lumen. Parasites were induced to feed and then preserved for TEM at the following intervals: just after feeding, 30 min after feeding, 1 h 30 min after feeding and 2 h after feeding. The specimens were then processed for TEM and sections cut through the intestine of each specimen were examined with the transmission electron microscope. Three types of vacuoles (V1, V2, V3) were detected in the gastrodermis. Vacuoles V1 have thick walls and are likely to be endocytotic, enclosing luminal contents at the surface of the gastrodermis. V2 vacuoles may be lysosomes that fuse with V1 vacuoles. V3 vacuoles may serve to dispose of residual digestive material into the lumen.

Ultrastructure of musculature of the marginal hooklets of Macrogyrodactylus congolensis, a monogenean skin parasite from the catfish Clarias gariepinus

The musculature of the marginal hooklets of adult Macrogyrodactylus congolensis (Prudhoe, 1957) Yamaguti, 1963 has been studied. Each marginal hooklet of M. congolensis is associated with three pairs of muscles. The possible role of these muscles in the operation of the marginal hooklet is discussed. Transmission electron microscopy has been used for the first time to study the marginal hooklets of M. congolensis. The handle articulates with the blade in the region of the guard. Internally, the handle, the proximal region of the blade in the articulation region and the distal pointed region of the blade consist of three layers. Distal to the articulation region, the blade consists of four layers with differing electron densities. A cavity is associated with the distal region of the blade and the handle. A cyton containing secretory bodies of different sizes and shapes was found in association with each marginal hooklet. The possible function of these secretions is discussed.

The first record of Macrogyrodactylus species (Monogenea, Gyrodactylidae) on freshwater fishes in Senegal with the description of Macrogyrodactylus simentiensis sp. nov., a parasite of Polypterus senegalus Cuvier

The first record of monogenean parasites of the genus Macrogyrodactylus Malmberg, 1957 on freshwater fish in Senegal is presented. Macrogyrodactylus congolensis Prudhoe, 1957 from the skin and Macrogyrodactylus heterobranchii N’Douba et Lambert, 1999 from the gills of Clarias anguillaris L. were found, representing new host records for these parasites. On Polypterus senegalus Cuvier, three Macrogyrodactylus species were identified, Macrogyrodactylus polypteri Malmberg, 1957, Macrogyrodactylus simentiensis sp. nov. and Macrogyrodactylus sp. M. simentiensis sp. nov. can be readily distinguished from the other Macrogyrodactylus species by the size of its hamuli and the shape of its marginal hook sickles. The marginal hooks on the anterolateral lobes of M. simentiensis differ in size and shape from those on the posterior margin of the haptor. Measurements and drawings of the haptoral sclerites of all five identified species are provided.