Myxosporidian parasites infecting fish are very dangerous parasites causing severe damage to a large number of economically important fishes especially in aquaculture. A survey of myxosporean parasites infecting four species of fishes from the River Nile in Egypt is conducted. One hundred and ninety-five out of 316 fish specimens with a percentage of 61.7% were found to be naturally infected with these parasites. Light microscopic examination of different tissues revealed the presence of 12 myxosporean species belonging to the family Myxobolidae. Four of the identified species are novel and the other eight species are redescribed. Myxidium sp.nov. a coelozoic species inhabiting the gallbladder of Labeo niloticus with its mature spores float free in bile was detected. These spores possess a fusiform, straight, or slightly crescentic shape with less pointed ends and two equal polar capsules. Three novel histozoic Myxobolus species infecting Oreochromis niloticus were identified. Myxobolus sp(1).nov. is a species inhabiting kidney tissue with ovoid spores exhibiting a small intercapsular appendix. Myxobolus sp(2).nov. and Myxobolus sp(3).nov. recovered from kidney and intestinal tissues. Spores of Myxobolus sp(2).nov. are elliptical in shape with an anterior end wider than posterior one. Their two polar capsules are ovoid to pyriform occupied nearly the first third of the spore body. Spores of Myxobolus sp(3).nov. are broader than long with nearly rounded or ovoid two polar capsules. Eight species of the recovered myxosporean parasites are redescribed, Myxobolus niloticus Fahmy et al., 1971 from pectoral, dorsal, and tail fins of L. niloticus, Henneguya suprabranchiae Landsberg, 1987, and Henneguya branchialis Ashmawy et al., 1989 are recovered from the gills and suprabranchial organ of the catfish Clarias gariepinus, respectively, Myxobolus naffari Abdel-Ghaffar et al., 1998 and Myxobolus imami Ali et al., 2002 are found in the kidney of Barbus bynni and L. niloticus, Myxobolus caudatus Ali et al. & Parasitol Res (2002) from Tail fin of B. bynni, Myxobolus fomenai Abdel-Ghaffar et al., 2008 from kidney and intestinal tissues of O. niloticus, Thelohanellus niloticus Abdel-Ghaffar et al., 2012 are observed in the gills of L. niloticus.

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In the present study, A cestode parasite was recovered from the intestine of the domestic sheep, Ovis aries (Bovidae) from the main slaughterhouse of Cairo, Egypt during the year of 2015. The parasite was observed attached to the wall of the host intestine by unarmed scolex with suckers only. Five out of 10 gastrointestinal tracts (50%) were found to be infected. Light microscopic examination showed that the adult worm of this species was whitish in color measured 421-492 (470±0.4) cm in length and 4.2-6.99 (5.6±0.7) mm in width. The scolex was with prominent four suckers measured 0.38-0.42mm in diameter. The scolex led into a long neck followed by segments. The mature segment was broader than longer, each proglottid measured 3.23-5.29 (4.6± 0.2) mm in width and 1.0-1.64 (1.4±0.02) mm in width and showed a two set of genital organs. The ovaries and the vitelline glands formed a ring on either side, median to the longitudinal excretory canals, while the testes were distributed throughout the central field or they may be concentrated toward the sides. Each ovary was of ovoid shape, measured about 0.16-0.19 (0.14±0.01) × 0.12-0.15 (0.13±0.02) mm and was located 0.8± 0.1 mm apart from the lateral side. The testes were concentrated on both sides. At the posterior border of each proglottid, a row of interproglotidal glands was arranged around small pits. Gravid segments measured 0.022-0.076 (0.048±0.2) mm in length and 2.10-5.02 (3.05±0.02) mm in width. The present parasite was compared with the previous species of the same host which showed that the parasite isolated is Monezia expansa.

Morphological characteristics and electrophoretic protein patterns were considered in the present study to distinguish between two types of clinostomatid metacercariae from Oreochromis niloticus fish caught from the River Nile at El-Minia district, Egypt. Fifty-two specimens of randomly collected 120 examined fish were infected with both Euclinostomum ardeolae and Clinostomum phalacrocoracis metacercariae or either. Euclinostomum ardeolae metacercariae were embedded in Oreochromis niloticus tissues of the kidney as round to oval greyish black cysts giving the area around faint black color with a 15% prevalence rate of infection. Cyst was of variable size (3-4 mm) and thin completely tight wall. Metacercaria is aspinose pyriform in shaped, long 6.5 wide 2.3 mm, of blunt anterior end but the posterior one is nearly rounded. Clinostomum phalacrocoracis yellow to orange in color cysts were detected in the pharyngeal region and branchial chambers and the prevalence rate of infection was 39.16%. They varied in size (4-5.2 mm) with a thin transparent membrane full of yellowish fluid. The body of metacercaria was elongated, tongue-shaped, and slightly wider in gonadic region, long 16.4 wide 4.01mm. Electrophoretic protein profiles were resolved using one dimensional SDS-PAGE stained with Coomassie Brilliant Blue R-250 stain. Encysted and excysted Euclinostomum ardeolae metacercariae showed bands of 61 kDa, 29 kDa, 28 kDa, 15 kDa and 14 kDa, while Clinostomum phalacrocoracis encysted and excysted metacercariae revealed bands of 61 kDa, 54 kDa, 32 kDa, 31 kDa, 20 kDa, 17 kDa, 15 kDa and 14 kDa. Conclusively, biochemical findings are in concordance with morphological characterization confirming both metacercariae to be of two distant species.

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