الفهرس 
Prevalence and seasonal dynamics of Trichodina species.Only 14 pages are availabe for public view
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Abstract
The present study is carried out to investigate the occurrence of external parasites on freshwater fishes in Manzala Lake and River Nile. At the same time the relationship between water pollution and external parasites was also studied. A total number of 948 fishes of different species are collected alive or freshly dead from different localities of Manzala Lake (n = 510) and River Nile (n = 438) during the period extended from August 2009 to the end of July 2010. The examined fish from Manzala Lake comprised 126 Clarias species, 28 common carp, 23 grass carp, 48 Mugil cephalus, 259 Oerochromis species 194 and 26 Tilapia zilli. While, fish species collected from River Nile comprised 130 Clarias species, 7 grass carp, 250 Oerochromis species and 51 Tilapia zilli. Regarding the parasitic infestation of different types of parasites detected in the affected fishes, protozoon parasites has the highest prevalence rate to be (68.82%) and (57.76%) followed by monogenea (40.98 %) and (23.97%), while crustacean parasites has the lowest prevalence rate to be (10%) and (4.57%) in Manzala Lake and River Nile respectively. Generally, higher infestation rate is recorded in Manzala Lake than that of River Nile. Approaching to seasonal prevalence of the revealed parasites, in case of Manzala Lake, protozoon parasites reached their highest prevalence in winter (78.95%) followed by autumn (76.99%) and spring (65.15%) while summer season had the lowest prevalence to be (55.3%). Monogenea prevalence also has its highest peak in autumn (53.1%) followed by winter (43.61%) spring season (37.88%) and summer (31.06%) respectively. The crustacean parasites has its highest prevalence in winter (15.79 %) followed by autumn (11.5 %) and summer (7.58 %) while spring season had the lowest prevalence (5.3 %). In case of River Nile, protozoan parasites has similar dynamics to that of Manzala Lake, as they had their highest peak in winter (71.88%) followed by autumn (59.29%), spring (52.17%) and finally summer. Monogenetic trematodes had their highest prevalence in autumn (27.43%) followed by winter (26.04%), spring (22.61%) to reach its lowest prevalence in summer (20.18%). The crustacean parasites has their highest peak in autumn (5.31%) and followed by summer (5.26%), winter (4.17%) to reach its lowest prevalence in spring (3.48%). Concerning the pollution degree, water samples obtained from different localities are examined chemically to measure biochemical parameters and heavy metals. The study showed that the water of Manzala Lake was more polluted with heavy metals than River Nile due to industrial and agriculture effluents that are considered to be the primary source of chemical pollutant such as cadmium, lead and mercury. The higher level of heavy metals, salinity and hardness has synergistic effect on the parasitic infestation rate. Concerning the revealed parasites, in the present study 9 species of external protozoa were revealed namely: Chilodonella hexastica, Trichodina californica, Trichodina cogwheeli, Trichodina fultoni, Trichodina heterodentata, Trichodina pediculus, Trichodina truttae, Apiosoma species and Henneguya branchialis, moreover 6 species of monogenic trematodes were detected namely: Ancylodiscoides longitubus, Quadriacanthus kearni, Cichlidogyrus arthracanthus, Cichlidogyrus tilapiae, Macrogyroductylus clarii and Schilbetrema acornis. Furthermore, 2 species of crustacean parasites were detected namely: Argulus japonicus and Ergasilus sarsi.