الفهرس 
Prevalence of infectionOnly 14 pages are availabe for public view
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Abstract
Clarias lazera and Bagrus bayad are freshwater Nile fish which are cowon i n Egypt and are most frequently consmed by l o c a l people, since they a t t a i n a large s i z e and have few spines i n t h e i r f l e s h , fdse, they are inportant since they are known to feed on nosquito larvae, and s n a i l s which act as vectors f o r b i l h a r z i a and l i v e r flukes, The present i n v e s t i g a t i o n was c a r r i e d out on 528 fish of these two species during the year 1977 and 1978, The aim was t o study the helminthic p a r a s i t e s found in these fish, An attempt has been lilade t o study various f a c t o r s influencing the prevalence of i n f e c t ionsby the dif f esent hellninthic p a r a s i t e s including the host sex, length, weight and ceasonal fluctuations. A det a i l e d illorphological and t axonouical study of the hellninthic p a r a s i t e s found during the study was given. Histopathological s t u d i e s mre also c a r r i e d out on the e f f e c t of Strigied metacercariae on the riluscle and l i v e r of Clams lazera, The r e s u l t s obtained can be sumnerized as follows: 1- In Clarias lazera, 268 f i s h were exmined, of these 63.3% were found t o harbour two t rematode gene r a ; Orientocreadimand Eumasenia, one cetsode genus Polyoncobothrim and two nematode genera ; Procamallanus and Paracarilallanus, In Bagrus bayad, of the 260 fish examined, 85% were infected with t h r e e trematode genera Haplorchoides, Nicolla and Acanthostomu% 2- The study of single, double and multiple infections i n Clasias lazera showed that the trematode genus Orientocreadium was the only genus which occurred singly, an the other hand, there was a close relationship between the trematode genera Eumasenia ayld Orientoceadim and between the cestode genus Polyoncobathrium and trema3iode genus Orientocreadium. It was also found that, when the f i s h was infected with nematode genera Procamallmus and Paracmallanus, neither trematodes nor cestodes w a s present. It was found th& the trenatode gem6.7 aplorch~ides was found i n a l l infected Bagrus bayad either singly o r associated with trematode genus Bicolla o r trematode genus -Bca nthos-to-m m. 3- The high prevalence of infection i n Female f i s h over males was recorded f o r the trematode genera that infect Clarias lazera and Bagrus bayad except for the genus Acanthostoruum which showed an increase i n male fish. The high prevalence i n female f i s h was also noticed for the cestode genus Polyoncobothrim that infect Clarias lazera, This high preu~3en ce of female inf e c t ion over males may be attributed t o the decrease i n the physiological resistance of the females during and after spawning, There was a slight increase i n the prexalence of infection by the nematode genus Paracamallanus i n male Claias lazera than feaales,,this uay be related t o the difference i n feeding habits,, dn the 3ther hand , the prev;ience of infaction with the nematode genus Pr~camalla-nus w as nearly smilax i n both male and female Clarias Xazera, T- his may be due the interaction of other environment a1 4- In the present investigation, it was noticed t h a t the prev a3 ence of inf action with the different helminthic parasites was also affected by the length and weight of the f i s h , In most cases, it is usually increased with the corresponding increase i n f i s h length and weight This increase was due t o the fact that the parasites are acquired from intermediate hosts not normally fed on by small individuals, 5- As regards the effest of seasonal fluctuations on the parasitic fauna of the f i s h , it was found that the p~ evaXence of inf ectim by different helminthic parasites was usually higher i n the Spring and Summer months. This was attributed t o the intensive feeding of the host, the wealth plankton ( containing the intermediate host) available at t h i s time of the year, the shortness of the period required f o r the development of the parasites and t o the f a c t t h a t the majority of f i s h examined during Spring and Swer were large fish that include a gre3t Proportion of gravid females, 6- k detailed morphological ’and taxonomicsl study of five species of trematodes ; Emasenicz aegyptiacus ; Orientocreadiw batrachoides ; Haplorchoides cahirinus ; Nicolla gallica ; kcanthostomwn absconditurn and licmthost~mwn spinicepa, one species of cestode ; Polyoncobothriwn clarias and two species of nematodes ; Paracamall anus cgathophmynx and Procamall anus -l.~ eviconchusw as al so given, The s t a t u s and v a l i d i t y of some of the helminthic genera are reviewed with pmtricular \ emphasi the taxonomical characters used f o r the differentation of the various species of the genus, The stlady revealed for the first tilne the occurrmce of the trematode species Nicolla gallica i n Bagrms bayad, 7- In the present study ; trematode metacercariae ~32%: recorded i n the muscles and l i v e r of Clarias 2-azera, This is the first record of these metacercariae i n the liver. According to the confirmation made by the British museum (Kiatural History) on the excysted metacercariae, these bodies were believed to belong to one of the members of the family Strigeida. Verification of t h i s identification can only be made possible &ter feeding experiments of the definitive hosts, those being appare-n2ly some water birds. Several attempts of experiment a1 infection of ducks were cried i n the present study to reach the adult Toms but unfortunately, negative results were obtained and further work is needed, The pathological effect ~f these metacercariae on the inuscle and Ziver was studied . It was found that the pathological effect was liuiited t o the vicinity of the parasite, This was due fa encapsulation of these metacercwiae. In the muscle,, the c d1la-w infilteration consisted of round cx%ls, fibroblasts, histiocytes and scanty polymarphonuclear leucocyteso The muscle f i b r e s in the neighbourhood of the cyst showed rilyocytolysis, In the l i v e r , the parenchymal hepatic cells immediately adjacent and surrounding the cysts were atrophied while the eighbouring cells presented fine cytoplasmic ve,cnI - zt ions.