الفهرس 
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Abstract
The present study was carried out to investigate the external and internal parasitic infection in some ornamental fishes collected from Alsaieda Aisha market in Cairo governorate and pet shops in Beni suef and Elfayoum governorates. A total of 439 ornamental fish 229 Carassius auratus and 210 Pangasiadon hypophthalmus were collected during period extended from June (2022) to February (2023) in different three seasons and subjected to clinical, parasitological and pathological examination.
The results of this study could be summarised as follows:
1. The isolated parasites were 10 types including 4 Protozoa, 2 Monogenea, 1 Digenea, 2 Crustacea and 1 nematode namely depending on their morphological identification:
• Trichodina sp.
• Ichthyophthirus multifiliis
• Chilodonella sp.
• Icthyoboda necator
• Dactylogyrus sp.
• Thaparocleidus caecus
• Gyrodactylus sp.
• EMC of Centrocestus formosanus
• Lernaea sp.
• Argulus sp.
• Capillaria sp.
1. Molecular identification of isolated parasite causing severe lesions in gills of P. hypophthalamus was carried out.
The parasite identified as Thaparocleidus caecus
2. The prevalence of parasites
The prevalence of parasitesin P. hypophthalmus was the highest and recorded 59.5% while in C. auratus was 47.2% .In C.auratus, protozoal infection recorded the highest prevalence rate (27.9%) followed by monogenea (15.3%) then crustaceans (12.7%) while digenea and nematode recorded the lowest prevalence rates (2.6%) and (0.4%) respectively.
On the other hand, P. hypophthalmus, monogenea infection recorded the highest infection rate (45.2%) followed by protozoans (21.9%) . The crustacean and nematode parasites were not found in P. hypophthalmus.
The peak of infection with parasites in C. auratus as recorded in autumn (54.8%) followed by summer (54.5%) while the lowest rate was in winter (20%). In Pangasiadon hypophthalmus, the peak of infection with parasites was recorded in summer (66.7%) followed by winter (66.3%) while the lowest rate was in autumn (45.7%).
3. It was noticed from these results that the prevalence of external parasites was more higher than that of internal parasites. Only two types of internal parasites were identified ( encysted metacercaria and nematode Capillaria) with prevalence lower than external parasites.
4. Gross examination of fish species infested with parasites revealed several abnormal manifestations
• In cases of Carassius auratus, the postmortem lesions were in the form of red elevated areas, spots of hyperemia, haemorrhagic nodules, white colored worm-like copepods appeared as a short piece of thread and protruded on different parts of the body, pale anemic gills or congested colored and tumid gills with considerable mucus discharge.
• In cases of Pangasiadon hypophthalmus, the macroscopic lesions were grey- white spots, finrot with excessive mucus on the body surface, haemorrhagic patchess appeared on the fin bases and mouth, round ulcer and congested gills with milky-like aspect and excessive mucus.
5. Histopathological findings
The histopathological picture revealed vacuolation, hyperplasia and necrosis of epidermal cells, a horse-shaped nucleus of Ichthyophthirius multifiliis, ulceration surrounding the site of parasitic attachment, different sections of Dactylogyrus sp. between and attached to the gill lamellae, hyperplasia, metaplasia, deformity and fusion of secondary gill lamellae, desquamation and necrosis in both primary and secondary gill lamellae in addition to leucocytic cell infiltrations mainly lymphocytes and macrophages, hyperplasia of gill cartilage and parasitic cyst surrounded by several layers of fibroblast like cells were noticed especially in case of encysted metacercariae and anchor worm penetrating skin in association with degeneration and desquamation of epidermal cells. Histopathological findings of different internal organs was absent.
Conclusion:
from the present study, it is concluded that
1) The most common parasites found on the skin and gills of goldfish (C.auratus) and Catfish (P. hypophthalmus) were Trichodina sp., Ichthyophthirus multifiliis, Chilodonella sp., Icthyoboda necator, Dactylogyrus sp., Thaparocleidus caecus, Gyrodactylus sp., EMC of Centrocestus formosanus, Lernaea sp. and Argulus sp. while the most common found in the intestines is Capillaria sp.
2) This study revealed that the prevalence rate of parasites in C.auratus and P. hypophthalmus is relatively high as well as the pathological findings induced by these parasites and might negatively affect the proper function of the skin and gills of the host, and could have a negative impact on fish health resulting in significant economic losses in this fish sp. and possibility of transmission to other fishes.
3) Estimation of seasonal prevalence in this study to direct the ornamental fish breeders to such parasites that infect fish in different seasons which acts as prophylactic measures.
4) The main pathological effect of the parasite species on the gill filaments of the fish in this study are primarily the destruction of the gill lamellae reduces the surface area available for efficient respiration results in significant mortality in aquaculture by impeding oxygen uptake.The outcome of the macroscopic and histological alterations brought on by parasite infections indicates that the infected fish’s gills and skin would not function properly.Therefore, the results of this study demonstrated that ectoparasitic infestations pose a significant risk to fish and can result in significant harm and loss of production.