الفهرس 
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Abstract
A total of 700 Tilapia species and 220 Clarias lazera were collected from Bahr Moies, El-Riah El-Tawfiki and their branches,
drainage canals and abbasa fish ponds.
Examination of the obtained fish revealed that only 57.78% Tilapia species and 51.87% Clarias lazera showed obvious clinical symptoms including excess mucus on the skin, emaciation with low body weight, darkness of the skin, black patches and or well demarcated black spots on the body surface especially at the area of the caudal peduncle and fins, minute haemorrhag’s on the skin, blindness and white spotted eyes,
enalrged abdomens and exophthalmia..
Gross lesions were mainly muscle nodules of variable size and colour, grey foci on the gill filaments, nodulated and marbling liver, spleen and kidneys, presence of large macroscopic cysts in the branchial cavity and kidney tissues, ascitic fluid in the abdominal cavity and eye pouch.
On microscopic examination encysted metacercariae, were found in 81.14% and 85% of the examined Tilapia species and Clarias lazera
respectively.
The highest incidence of metacercarial infestation among both examined and infested Tilapia species was found in the muscles of the posterior third (77.57% and 95.60%) followed by middle third (69.14% and 85.21%), anterior third (62.7% and 77.28%), gills (62% and 76.4%), liver (29.57 and 36.44%), kidneys (23.29% and 36.44%), spleen (16% and
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19.72%) eye (16.20 and 13.14%), skin (12.26% and 15.14%) and fins (9.00 and 11.09%).
In Clarias lazera the maximum incidence of metacercarial infestation in both examined and infested fish was found in the muscles of middl third (85.00% and 100%) followed by anterior third (71.36% and 83.95%), posterior third (62.27% and 79.14%), liver (49.55% and 58.28°M, gills (40.91% and 48.12%), kidneys (31.36% and 36.90%) and
spleen (19.55 and 22.99%).
The highest incidence of metacercarial infestation in Tilapia species was found in fish of 100-150 gm and that measured 20-25 cm in length, while in Clarias lazera it was found in fish less than 200 gm weight and of length less than 30 cm.
The highest incidence of infestation among tilapia was found in July (96.22%) and March (94.44%) and the lowest in November (65.21%). In Clarias lazera the highest incidence was found in June (100%) and November (100%) while the lowest recorded in January (68.42%).
The maximum incidence of infestation in tilapia was recorded during summer (90.30%) followed by spring (87.58%) and winter (85.96%) while the lowest was reported during autumn (65.57%). In Clarias lazera the highest infestation rate was found in summer (91.24%) followed by spring (87.43%) and winter (83.26%) and the lowest was
obtained during autumn (70.04%).
The maximum number of encysted metacercariae per gram muscles and other organs among tilpia was found in the muscles of the posterior third (34.936 /gm) followed by that detected in middle third (23.21/gm),
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anterior third (13.23/gm), liver (4.05), fins (3.38), skin (3.44), kidney (2.84), spleen (1.92), eye lenses (1.24) and in branchial cavity (0.16).
The highest number of metacercarae (per gram) was recorded during spring in the muscles of posterior, (62.87), middle (38.36) and anterior third (21.35) as well as in skin (12.46), fins (11.19). Liver (5.42), kidneys (4.86) and spleen (2.94). While the lowest number was detected
during autumn.
In Clarias lazera the maximum number of encysted metacercariae per gram muscle and other organs was reported in muscle of middl third (51.893) followed by anterior (33.294), posterior third (24.738), liver (5.86), kidneys (3.66) and spleen (1.52), with respect to the effect of season, the highest number was found during winter and the lowest recorded during autumn.
The encysted metacercariae obtained from Tilapia species were identified as Prohemistomatide, Diplostomatide Haplorchide, Heterophyide, Echinostomatide, Euclinostomatide and Clinostomatide, metacercariae, while those recovered from Clarias lazera were found to be belonging the families Prohomistomatide, Diplostomatide, Haplorchide and Cyanodiplostomatide.
Histopathological reactions around the encysted parasite in fish muscle and organs varied in severity according to the species of the infested metacercariae. In muscle the inflammatory reaction was represented by aggregation of lymphocytes, macrophages, esinophilic granular cells and melanin-carrying cells. Degenerative and necrotic muscular changes beside pressure atrophy, were also found. Kidney
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tissues showing aggregation of lymphocytes, macrophages and excessive number of melanin-carying cells, in addition vacuolar and granular degeneration of tubular epithelium and somesort of haemorrhage between kidney tubules and around parasitic elements. Some tubules suffered from necrobiotic changes with coagulative necrosis of their epithelium atrophy of capillary tuft of the glomeruli and edema in Bawman’s capsule.
Moreover the infested liver showed granulomas and parasitic nodules, dissociation of pancreatic acini and coagulative necrosis of hepatocyts. The infested gills showed presence of multiple small sized parasitic cyst causing pressure atrophy on cartilagenous specules of the gill filaments or ending with cartilagenous hyperplasia or metaplasia.
All the previously described species of metacercariae were experimentally fed to week-old chicks, baby chicks, day-old ducklings (pickini and balady), squabs, quails, herons and moorhens.
Heavely infested birds showing obvious clinical symptoms and lesions and their intestine contained different species of trernatode worms. The recovered trematodes identified as Diplostomum ibis sp. nov., Diplo.vtomurn niloticus sp. nov., omithodiplostomum, Echinochasmus japonicus, Echinochasmus beleocephalus, Nephrostomum ratnosum, Apharyngistrigia ibis, Prohetnistomum vivax, Mesostephanus (M.) appendiculatus, M. fajardensis, M. flapi, Paracenogonimus ovatus, Holostephanus volgensis, Heterophyes equalis, Heterophyes dispar, Pyigidiopsis’ genala, Pyigidiopsis summa, centroceslus armatus, A•cocotyl mncintochi, Metagonimus yokojawai, Haplorchis pumilio, Haplorchis yokojawai and Haplorchis disca.
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Histopathological changes in the intestine of infested birds with mature worms showing hyperplastic proliferation of mucus gland at the wall of intestinal crypts especially at the basal portion and in areas neighbouring to attachement of parasite while at the site of the parasite the intestinal villi revealed lake of mucus glands with necrosis of epithelial lining, dilated blood vessels in lamina propria associated with few number of inflammatory cells. Sometimes the intestine showing sever destruction of the epithelial lining and their crypts displayed excessive haemorrhages and leucocytic infiltration between intestinal glands. In some cases the intestinal lumen appeared as a bag filled with necrotic debris, haemorrhage’s and few number of inflammatory cells.
For studying the effect of temperature on the viability of the EMC, a total of 422 Tilapia fish and 120 Clarias lazera were collected from Bahr Moies, El-Riah El-Tawfiki and their branches and drainage canals.
Regarding to the effect of heat on the viability of encysted metacercariae, boiling of the infested tilapia and Clarias lazera, for 5 minute were sufficient to loss the viability of the cysts, while frying of infested tilapia and clarias lazera for 5 minute were quite sufficient to loss the viability of the cysts found in small and medium sized fish while 10 minute were required for cysts laden in the muscles of large sized fish.
Grilling of the infested tilapia on each side for 5 minute were sufficient to lose the viability of encysted metacercariae found in small size, while in medium sized fish the viability lost after 10 minutes.
Chilling of the infested tilapia at 4 °C revealed that the encysted metacacercariae of Diplostmatide and Echimostomatide. showed rapid
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lose in their viability on the second day post chilling. On the other hand the encysted metacercariae of Prohemistomatide, Haplorchid, Heterophyid, Diplostomatide, Euclinostomatide and Echinostomatid. loss their viability completely at 18,17,15,14,8 and 5 day post chilling respectivelly. While the encysted metacercariae of Prohemistomatidae, Haplorhcide, Diplostomatide and Cyanodiplostomatide recovered from the infested Clarias lazera lost their viability at 14,12,14 and 16 day post chilling respectivelly.
The encysted metacercariae infested Tilapia fish lost their viability by freezing at -4°C or -5°C, -10°C, 15°C and -20°C for Prohemistomatide after 48, 32, 24 and 16 hours post freezing (PF) respectively, for Haplorchid after 40, 32, 24 and 16 hour PF, respectively, for Diplostomatide after 32, 24,16 and 8 hours PF respectively; for Echinostomatidae at 24, 16,16 and 8 hours PF respectively and for Euclinostomatidae after 32,24,16 and 8 hours PF respectively.
In infested Clarias lazera the obtained encysted metacercariae lost their viability by freezing at -4°C or -5°C, -10°C, -15°C and -20°C for Prohemistomatide after 32,24,16 and 8 hours PF respectively, for Haplorchide after 32, 16,16 and 8 hours PF respectively, for Diplostomatidae after 24, 16,16 and 8 hours PF respectively and for Cyanodiplostomatidae after 32,24, 16 and 16 hour PF respectively.