Variation in the sex ratio of Rhabdochona fortunatowi (Spirurida: Rhabdochonidae) in Capoeta capoeta gracilis (Cypriniformes: Cyprinidae), relative to levels of XXXX , host size and temperature.

@entity281 @entity2199
In the present study, 81 specimens of Capoeta capoeta gracilis (Keyserling, 1861) were collected from the Shiroud River, the Caspian drainage basin, Iran in June and October 2007. The fish were examined for @entity281 with the @entity2199 Rhabdochona fortunatowi (Dinnik, 1933). @entity2199 were counted and sexed, then the sex ratio and intestinal site preference of the R. fortunatowi individuals and the intersexual interactions of the parasites were investigated. Significant differences were observed in the prevalence and intensity of @entity281 in relation to host size and sampling season, but not host sex. Parasite burden (mean intensity) was higher in October than in June and the results revealed a decrease in female-to-male sex ratio (FMR) in the fish in October compared to the ones in June. In other words, as the mean intensity of @entity281 of R. fortunatowi increases, the proportion of male worms increases, too. The female-biased sex ratio in June was replaced by a male-biased one in October. @entity2199 distribution rose to a significant peak in the mid-region of the fish intestine relative to the anterior and posterior parts. Some changes in the distribution of male and female worms in different parts of the host intestine were also observed during June and October. Density-dependent selection and intersexual competition seem to be the main factors driving such a shift in the sex ratio and its variation in different parts of the host intestine.
