الفهرس 
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Abstract
Fishes offer great hope in solving the problem of animal protein deficiency. The African sharp-tooth catfish, Clarias gariepinusis one of the most popular fish kinds in Egypt since it represents an important source of animal protein and had a low level of cholesterol. The present study includes detailed observations on the ecological, morphological, anatomical, and molecular characteristics of the parasitic helminths infecting the catfish, C. gariepinus from the Damietta Branch of the River Nile, Dakahlia Governorate, Egypt. A total of 154 specimens of the catfish C. gariepinuswere collected in the period from March 2020 to February 2021. These parasites were studied using a Phase-contrast microscope, scanning electron microscope and molecular tools. Ecological studies: In the present study, the detected parasites are one monogenean,Macrogyrodactylusclarii from the gills, three digeneans, Orientocreadium batrachoides, Eumasenia bangweu lensis and Sanguinicola sp. from the intestine, two cestodes Tetracampose ciliothecaand Monobothrioides chalmersiusfrom the intestine and two nematodesParacamallanus cyathopharynx andProcamallanus pseudolaeviconchus from the stomach and the intestine. Except for Sanguinicola sp., most digeneans, cestodes, and nematodes of C. gariepinus were recorded throughout the year, except for a few months. However, thegill monogenean parasite M. clarii was missing during 6 months of the year (February to June and August) and the digenean Sanguinicola sp. was absent in all months except October, December, January, and February. The digenean group was the most dominant followed by the cestode and nematode groups respectively. Most gastrointestinal parasitic species were eudominant or dominant except P. pseudolaeviconchus and Sanguinicola sp. which were subdominant and subrecedent, respectively. The catfish,C. gariepinus recorded a considerably high overall infection rate with parasitic helminths (87.66%). The nematode parasites of the present study attained the highest infection rate over the digeneans, monogeneans and cestodes. Each parasite species reacted differently towards the seasonal changes over the study period. However, E. bangweulensis was the only parasite to show a highly significant difference in all ecological parameters between different seasons whereas T. ciliotheca showed a seasonal significant difference only in the mean prevalence and mean abundance. All helminth parasites of C. gariepinus showed no significant difference in their mean prevalence between males and females while P. pseudolaeviconchus was the only parasite to show a significant difference between males and females in the mean abundance and mean intensity. The present investigation showed variations in the relationship between helminth parasite infection levels and proposed classes of host condition factor. Morphological, anatomical, and molecular studies Paracamallanus cyathopharynx (Balylis,1923) Yorke et Maplestone, 1926 The present nematodeparasite has been described in detail using phase contrast microscopy and scanning electron microscopy (SEM), particularly the hard parts of the buccal capsule, digestive system, reproductive system of both male and female and surface structures including all openings (mouth, vulva, anus, and cloaca), body transverse striations, cephalic papillae, deirides, caudal alae, caudal papillae, and tail processes. Moreover, molecular analysis and phylogenetic studies were done for the first time for this species in Egypt. SEM observations have revealed the presence of 4 small triangle-like cuticular buccal lips on the oral opening (2 dorsal and 2 ventral) and each buccal lip is associated with a cuticular elevated process, features which were not previously described in Paracamallanus spp. The buccal capsule is well-developed and divided into two main portions, anterior and posterior. The anterior portion consists of two wide lateral valves. The inner surface of each lateral valve bears nine strong longitudinal ridges. The terminal part of each longitudinal ridge was found to bear a tooth-like structure on the inner border of the oral opening. There are dorsal and ventral tridents, each consisting of a basal anterior spherical plate and three arms, with the two lateral arms longer than the median one. In SEM, three depressions are seen on the cuticular surface of the trident, an anterior, triangle-shaped depression and two posterior elongated depressions between the inner border of each of the lateral arms and the median arm. The general surface in all hard parts comprising the trident is almost smooth while in older specimens, forms a narrow, shallow depression at its middle line. Each of the lateral plates of the buccal capsule forms a triangle-like structure with the outer edge longer than the inner and posterior edges. The surface covering of the sclerotized lateral plates is smooth, but their outer and posterior borders have an irregular outline. There is a shallow longitudinal channel between the inner borders of the lateral plates. Four large cephalic papillae were observed in mostexamined specimens. In both male and female P. cyathopharynx, the head region has apparently large longitudinal cuticular ridges in addition to comparatively smaller transverse cuticular striations. Transverse annulations(striations) of P. cyathopharynxare distinct and in relaxed specimens appear separated by thin shallow furrows while in contracted specimens, these striations are overlapped. The tail region of male possesses 10 pairs of alaeal pedunculate papillae (5 precloacal and 5 postcloacal), 2 pairs of sessile cloacal papillae and a single pair of prealaeal papillae. The postcloacal papillae lying posterior and very close to the cloacal opening are grouped into 3 pairs, closely adjacent to each other. In P. cyathopharynx of the present study, only the right copulatory spicule was observed and no evidence in all specimens examined of the left copulatory spicule.The sclerotized copulatory spicule was found to consist of 3 main regions: a short wide base, a long tubular shaft with ridged surface, particularly at its base and a terminal blade with 2 lateral wings enclosing a median channel terminating in a sharply pointed needle-shaped process. The blade possesses a short pointed lateral process at its base. Moreover, the copulatory spicule was found to be associated with several longitudinal groups of muscle fibres categorized into 2 types: retractor and protractor muscle fibres. In the present study, molecular characteristics, and the phylogenetic position of P. cyathopharynx within the family Camallanidae and other closely related families, Raphidascarididae and Anisakidae, were evaluated based on analyses of the internal transcribed spacer 1 and 5.8S ribosomal RNA gene. The study has confirmed the identity and validity of the present nematodeP. cyathopharynx. A sequence (543 bp long) of the internal transcribed spacer 1 and 5.8S ribosomal RNA gene of P. cyathopharynxwas done and deposited in the GenBank under accession No. MW704280.The present phylogenetic analyses showed that the camallanid P. cyathopharynx from Egypt andParacamallanus sp. (KF652083) (family: Camallanidae) from India have a much closer relationship than with Hysterothylacium species (family: Raphidascarididae). Procamallanus (Procamallanus) pseudolaeviconchus Moravec and Van As, 2015 The present study provides a detailed description of the nematode, Procamallanus (P.) pseudolaeviconchus using a phase-contrast microscope (LM) and scanning electron microscope (SEM), particularly the buccal capsule, digestive system, reproductive system of both male and female and surface structures including all openings (mouth, vulva, anus, and cloaca), body transverse striations, cephalic papillae, deirides, caudal alae, caudal papillae, and tail processes. In the present study, the inner surface of the buccal capsule, although it is generally smooth, possesses a slightly thickened region of its wall just anterior to its basal ring, a feature that wasn’t described in the previous descriptions of P. pseudolaeviconchus. The ovary was found to be telogonic and differentiated into germinal, growth and maturation zones. The germinal zone begins as cap-like cell followed by a cylindrical, tubular, structure packed with oogonia. In the growth zone, the young oocytes are packed together and attain pentagonal and hexagonal shapes. In the widened posterior region of the ovary, the oocytes reach their maximum maturation and can be found in 4differentiated forms. Most of these forms contain secretory bodies of different sizes and forms including single and aggregated dense granules, small vesicles with central dense granules and large vacuoles with multivesicular bodies. Conspicuous constrictions are found between the ovary and oviduct, oviduct, and seminal receptacle, and between the seminal receptacle and uterus. The uterus begins as a wide chamber containing 3-4 rows of developing embryonated larvae then decreases in size as it proceeds posteriorly where it contains 1-2 rows of developing embryonated larva. The vaginal tube is covered externally by an epithelial layer and supported by transverse muscle fibres. It opens into the vulva at the ventral surface of the worm. The opening of the vulva is guarded by 2 elevated conspicuous lips. In old female worms, the uterus is filled with first stage rhabditiform larvae. Each larva consists of a muscular oesophagus and intestine. The male reproductive system is monodelphic which comprises a single testis, seminal vesicle, vas deferens, cloacal opening, and accessory organs that include spicules and genital alae. The testis is tubular structure consisting of a germinal, growth and maturation zones. The germinal zone is small in diameter and filled with spermatogonia while the growth zone is larger in diameter and contains several rows of germ cells (spermatocytes) which are more compact and acquire a cuboidal profile. Two copulatory spicules (right and left) were observed in the present study.The right spicule is larger and more sclerotized than the left one. The present SEM observations of male revealed fourteen pairs of caudal papillae. These papillae are categorized into nine pairs of precloacal papillae, one pair of adcloacal papillae (anterior to the cloaca) and four pairs of postcloacal papillae, of which three pairs are subventral, whereas one pair is situated close to the posterior extremity of the tail. The surface structure of the alaeal papillae is described for the first time in P. pseudolaeviconchus. Each papilla appears as cone-shaped structure with a terminal opening containing a small, short process. The surface of the cone shows radial cuticular ridges arranged in 3 circles (levels), an outer short (distal) circle, a middle relatively long (median) circle and a long and wide inner (basal) circle.