Factors affecting prevalence and site preferences of heterophyid metacercariae (MC)
were investigated in this study. A total of 173 specimens of a freshwater fish, Tilapia
zilli were collected during autumn 2008, winter 2009 and summer 2009, from Ismailia
fresh water canal, Egypt. Results showed that the total prevalence of heterophyid
MC was 95.37%. The heterophyid MC consisted of Haplorchis yokogawi (47.4%), Pygidiopsis
genata (21.4%), and Phagicola ascolonga (93.64%). H. yokogawi MC was detected in striated
muscles, P. ascolonga in liver and kidney while, P. genata was detected in muscles,
liver and kidney. The aggregation indices showed that all MC were aggregated and the
P. genata was the most highly aggregated followed by H. yokogawi and then P. ascolonga.
Responses of the heterophyid MC to host sex, weight and season greatly varied according
to species of MC. Different responses of interaction for heterophyid MC intensity
were found by GLIM analysis and this variation dependant on the type of infection
(single or mixed infections). Factors affecting site preference of heterophid MC infection
were discussed and further studies in other locations are required to examine the
factors affecting site preference.