Parasitol Res (2003) 91: 390–397 DOI 10.1007/s00436-003-0978-3 ORIGINAL PAPER M. A. Ali Æ A. S. Abdel-Baki Æ T. Sakran R. Entzeroth Æ F. Abdel-Ghaffar Light and electron microscopic studies of Myxobolus stomum n. sp. (Myxosporea: Myxobolidae) infecting the blackspotted grunt Plectorhynicus gaterinus (Forsskal, 1775) in the Red Sea, Egypt Received: 1 July 2003 / Accepted: 30 July 2003 / Published online: 18 September 2003 Ó Springer-Verlag 2003 Abstract A new myxosporean parasite, Myxobolus sto- this effort by investigating myxosporean parasites in the mum n. sp., is described from the oral cavity and lips of Red Sea, Egypt. The present study deals with a new the blackspotted grunt Plectorhynicus gaterinus (For- species of Myxobolus infecting the blackspotted grunt sskal, 1775) in the Red Sea, Egypt. The parasite was (local name gatrina), Plectorhynicus gaterinus (Forsskal, observed as tiny aggregates of whitish cysts hardly no- 1775). The parasite is described by light and electron ticed within the muscles of the oral cavity, especially microscopy and its histological implication is also pre- within the lips. The spores were subspherical and mea- sented. sured 8.5·6.5 lm. Polar capsules were equal, pear- shaped, occupied about half of the spore length and measured 4.4·2.4 lm. Histological evaluation of the Materials and methods infection revealed no significant impact on the host. The ultrastructure of the plasmodial wall and sporogenesis of Live or freshly caught fish samples were collected from boat- the present species followed the usual pattern valid for landing sites, fishermen and sometimes from the markets of Suez and Hurghada at the Gulf of Suez and Red Sea, respectively. A most studied myxosporean species. total of 30 fish (16 from Suez, 14 from Hurghada) were examined. Descriptions and measurements of spores followed the guidelines of Lom and Arthur (1989). Measurements were based on 30 spores Introduction and data were presented as mean ±SD (range). For histology, the infected parts were fixed in 10% phosphate-buffered formalin, embedded in paraffin, sectioned and stained with haematoxylin and There is considerable information on the myxosporean eosin. For the electron microscopy, small intact cysts with minimal parasites from different parts of the world. The African surrounding tissue were isolated and fixed in 3% glutaraldehyde in Myxosporea are being extensively studied in many parts 0.1% sodium cacodylate (pH 7.4), washed in the same buffer and of the continent, like Cameron, Benin and Egypt. post-fixed with 2% OsO4 in the same buffer. The tissue pieces were dehydrated in graded ethanol and embedded in araldite. Ultra- However, the marine myxosporean species are rarely sections were stained with uranyl acetate and lead citrate and investigated in Africa. Few studies have been carried out examined with a Philips (model 208) electron microscope at on marine fish, e.g. Fantham (1919, 1930), Fall et al. 80–100 kV. (1997) and Ali et al. (2001). The present work continues Results A. S. Abdel-Baki (&) Æ T. Sakran Beni-Suef Faculty of Science, Light microscopy Zoology Department, Cairo University, Egypt E-mail: [email protected] The infection was observed as tiny aggregates of whitish cysts hardly noticed within the muscles of the oral cavity M. A. Ali National Institute of Oceanography & Fisheries, and more frequently within the lips. These aggregates Egypt were clusters of ovoid cysts of variable numbers (up to eight cysts per fish). A single plasmodium measured R. Entzeroth Institute of Special Zoology and Parasitology, 406 lm (400–410 lm) in length and 255 lm (250– Technical University of Dresden, Germany 270 lm) in width. The prevalence was 6/14 (42.8%) in F. Abdel-Ghaffar Hurghada samples and 4/16 (25%) in Suez samples. In Faculty of Science, Zoology Department, most cases, the oral cavity of the grunt fish was infested Cairo University, Egypt with pranizae or larval gnathid isopods. 391 Spores Histology The spores were subspherical in frontal view (Figs. 1, The plasmodia were distributed throughout the muscle 11). They measured 8.5±0.8 lm (7.0–10.0 lm) in of the oral roof. The parasite formed plasmodia among length and 6.5±0.6 lm (5.5–7.5 lm) in width. Polar the muscle fibres (Fig. 2). Mature spores were located capsules were equal, pear-shaped and occupied centrally inside the plasmodia, while the developmental about half of the spore. They measured 4.4±0.5 lm stages were peripherally arranged (Fig. 4). A thin layer (4.0–5.0 lm in length and 2.4±0.4 lm (2.0–3.0 lm of the host connective tissue encapsulated the plasmodia in width. The polar filament showed mostly five and (Figs. 3, 4). No host infiltration was apparent around rarely six coils oblique to the main axis of the polar the developing parasite. capsules. Electron microscopy Plasmodia Fig. 1 Fresh spores of Mxyobolus stomum sp. n. with Nomarski interference contrast. Bar 10 lm The plasmodial wall of the present species was clearly Fig. 2 Longitudinal section of an infected muscle (M), showing the demarcated into an outer ectoplasm and an inner plasmodium (P) surrounded by a thin layer of connective tissue endoplasm (Fig. 5). External to this wall was a thin (CT). Bar 60 lm Fig. 3 Semithin section of an infected muscle (M), showing the layer of connective tissue in contact with the muscle plasmodium (P) surrounded with a thin layer of connective tissue of the host (Fig. 5). The plasmodia were surrounded (CT). Bar 30 lm by a single-unit membrane from which short pinocy- Fig. 4 Magnified part of a semithin section of an infected muscle totic channels and vesicles extended nearly close to (M), showing the plasmodium (P) surrounded with a thin layer of connective tissue (CT). The plasmodia contained developmental the periphery of the endoplasmic zone (Fig. 5). In stages (DS) at the periphery and mature spores (Sp) close to the the outer zone of the endoplasm, there were centre. Bar 10 lm numerous mitochondria, vegetative nuclei, generative 392 Fig. 5 A part of the plasmodium of M. stomum sp. n., showing the plasmodial wall composed of ectoplasm (Ec) and endoplasm (En). Externally, the plasmodium was surrounded by a layer of connective tissue (CT)in contact with the muscle of the host (M). Some host nuclei (HN) were observed close to the plasmodium membrane. The plasmodium was bounded by a single-unit membrane from which pinocytotic channels (arrows) and vesicles (V) originated. The periphery of the endoplasm contained numerous generative cells (GC) and pansporoblasts (Ps), surrounded by a large number of mitochondria (m). Bar 2 lm cells and developing pansporoblasts, while the central all the stages of spore formation were observed, each part of the plasmodia contained mature spores spore developed from five cells: two peripherally ar- (Fig. 5). ranged valvogenic cells, a pair of capsulogenic cells and a binucleated sporoplasm (Fig. 10). As spores proceeded toward maturation, there was structural progress in Sporogenesis capsulogenesis, sporoplasm maturation and valvogene- Sporogenesis was asynchronous and early sporogenic sis (Figs. 8, 9, 10). stages were concentrated in the peripheral areas (Fig. 5). Generative cells, the earliest recognizable stages of spo- Capsulogenesis rogenesis, were nearly spherical, with a diameter of 4 lm and limited by a double-unit membrane. The cytoplasm Capsulogenic cells were found at the apical pole of the of the generative cells contained numerous ribosomes developing spore and, together with the sporoplasm, and a large eccentric nucleus with peripherally arranged formed a central core that was ensheathed by valvogenic chromatin material (Fig. 6). The generative cells were cells (Fig. 10). The capsulogenic cells were characterized always surrounded by numerous mitochondria. by the presence of distended cisternae of the endoplas- Sporogenesis began with the union of two generative mic reticulum (Fig. 8). The differentiation of the cap- cells. That union resulted in an early pansporoblast, the sulogenic cell started with appearance of a club-shaped pericyte containing the sporont (Fig. 7). Although not structure, which was the initial stage of the capsular 393 Fig. 6 A generative cell with large voluminous eccentric nucleus primordium (Fig. 8). Gradually, the initial stage differ- (N), which contained dark chromatin material at the periphery. entiated into the bulbous primordium and the associated The cell was bounded by a double-unit membrane (arrowheads). Bar 300 nm external tube, which was closed at the distal end. The Fig. 7 Two-cell pansporoblast consisting of a pericyte with its external tube was later internalized into the primordium nucleus (N1), enveloping the sporont cell with its nucleus (N2). Bar to make the polar filament coils with 5–6 turns (Figs. 9, 1 lm 10). The developing polar capsule had a homogenous Fig. 8 A capsulogenic cell containing capsular primordium (CP), core of medium electron-density, surrounded by an external tube (ET) and destined cisternae of endoplasmic reticulum (asterisks). Bar 300 nm electron-lucent layer and an outer layer of medium Fig. 9 Transverse section through maturing spores, showing density (Fig. 9). A stopper with a triangular cap-like almost mature polar capsules. The polar capsule was composed cover plugged the apex of each mature polar capsule of an electron-dense outer layer (arrow), a central translucent layer (Fig. 9). Maturation of the two polar capsules was (Lu) and an inner dense core with polar filament coils (PF). A stopper (Pl) with a triangular cap-like cover (Cp) plugged the apex usually synchronous (Fig. 10). of the polar capsule. Bar 300 nm Fig. 10 Longitudinal section through mature spores, showing two synchronously developed polar capsules (PC) with polar filament Sporoplasm coils, sporoplasm (Sp) with two nuclei (SN1, SN2) situated closely side by side, small dense bodies (sporoplasmosomes; arrowheads) and As soon as the polar capsule primordium appeared, the valvogenic cells (VC) with valve-forming bodies (VFB).