الفهرس 
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Abstract
The present study was conducted during the period between January 2021 to December 2021 in the department of Parasitology, Faculty of Veterinary Medicine, Assiut University to determine the prevalence of parasites of freshwater fish (Catfish and Tilapia) in Assiut governorate.
A total of 200 fish samples (100 Nile tilapia and 100 Catfish) were collected randomly from different localities in Assiut governorate, the samples were examined for presence of external and internal parasites and investigated their seasonal abundance, size and sex susceptibility to the infection.
Our study revealed that about 162 fish samples were infected with infection rate 81%. The prevalence rate in Nile tilapia and catfish was (80% and 82%) respectively. The total recovered external parasitic infection was Monogenean and External protozoa with (20.5% and 8.5%) respectively. In Nile tilapia monogenan were (31%) including Gyrodactylus, Dactylogrus and Cichlidogyrus with (5%, 4% and 23%) in another hand in catfish 10% include Gyrodactylus and Dactylogrus (2% and 8%). The infection rate of external protozoa was (10% and 7%) in Nile tilapia and catfish respectively. The species recovered from Nile tilapia were Trichodina with 6% and Icthyophthirius multifiliis with 4% and in catfish Henneguya with 2% and Icthyophthirius multifiliis with 5%.
Our study revealed that, sex and size effects on distribution of infection in case of monogenean, the infection rate of females were (51.6% and 30%) and in males were (48.4%and 70%) in Nile tilapia and catfish respectively. The infection was insignificantly higher in females than males, while the infection rate with external protozoa was similar in both males and females (50% in both) in Nile
tilapia while in catfish the infected rate was in females were (57.1% ) and higher than males were (42.9% ).
Regarding seasonal variation, the highest infection rate of mongenean in winter with (35.5%, 30%) and the lowest rate was in autumn with (16.1%, 20%) in Nile tilapia and catfish respectively, while external protozoa the highest infection rate in Nile tilapia was in spring with (40%) followed by summer and autumn (30%), in winter zero was infection, while in catfish the infection only shown in summer with (100%).
The total internal parasitic infection was 60.5% with (41% and 80%) in Nile tilapia and catfish, the recovered parasites were trematodes orientocreadium batrachoides, the cestode were (Polyochobothrium clarias and Monobothrioides(, nematode were (Contracaecum and Paracamallanus sp.), Acanthocephala and internal protozoa were (Myxobolus, Isospora, Entamoeba and eimeria), the rate of infection was ( 14.5%, 13.5%, 7% , 25% and 13%) respectively.
Concerning trematodes the recovered species was orientocreadium batrachoides (3% and 26%) in Nile tilapia and catfish respectively. The infection was in male, in summer only and large sized fish in Nile tilapia, while in catfish was significant higher in females, the highest infection was in summer and the lowest in winter and small sized fish, while cestodes recovered was (polyochobothrium clarias 6% and Monobothrioides 21%) in catfish only. The infection was insignificantly higher in females, small sized fish and highest in summer, lowest in winter and autumn. The nematodes recovered were Contracaecum 2% in Nile tilapia and Paracamallanus sp. 12% in catfish, the infection rate was insignificantly higher in males, highest in summer and the lowest in winter and autumn and high in small sized catfish.
Regarding to Acanthocephala (acanthosentis tilapiae) was 25% in Nile tilapia; the infection was insignificantly higher in females and the highest infection in summer and the lowest in autumn.
Regarding to internal protozoa the recovered species was (Myxobolus, Isospora and Eimeria (2%, 1% and 8%) respectively in Nile tilapia and Entamoeba only in catfish with 15%. The infection insignificant higher in females and highest in winter and small sized Nile tilapia, while in catfish the infection significant higher in males, highest in summer and small sized fish.
Concerning Public health importance encysted metacercariae have the upper hand when it comes to parasitic disorders in fish. Metacercariae are extremely common, especially in freshwater fish. Encysted metacercaria classified into two types macroscopic and microscopic EMC. The infection rate of macroscopic EMC was 37% in Nile tilapia only, while total microscopic encysted metacercaria was 62% with (58% and 66%) in Nile tilapia and catfish respectively. The highest infection rate of macroscopic was in summer and lowest rate in autumn and high in females, while microscopic EMC the highest infection in summer and lowest rate in autumn, high in males and small sized fish.
Experimental infection was designed for further identification of adult worm after digestion and collection of EMC, that used for orally infection of albino mice, after 5th day the mice were slaughtered, dissected and the adults worm were isolated from the intestine for identification of the species, also for more confirmation SEM was used for more differentiation and identification. The recovered worms were Prohemistomum vivax and Mesostephanus sp., which belong to family Cyathocotylidae.
This study revealed that the different parasites were widely spread between fresh water fish and have a direct effect on health of the fish and also direct effect on economy and productions so control measures should be put in consideration for prevention of further spread, also the human should take care when dealing with fish to prevent the spread of zoonotic parasites specially that transmitted through consumption of under cooked fish.