Molecular characterisation and infection dynamics of Dentitruncus truttae from trout (Salmo trutta and Oncorhynchus mykiss) in Krka River, Croatia.

Dentitruncus truttae (Acanthocephala, Palaeacanthocephala) is an intestinal parasite of fish that can cause extensive damage to the host digestive tract, yet little is known about its epidemiology and genetic variability. It is a member of the Illiosentidae family with a worldwide distribution restricted to parts of southeast Europe. Its usual host is brown trout (Salmo trutta), but we report here the first detection in the intestine of rainbow trout (Oncorhynchus mykiss). We examined the physiology of D. truttae-infected S. trutta and O. mykiss, seasonal and spatial variability of D. truttae infections, and genetic variability of the parasite population in Krka River, Croatia. D. truttae was more abundant in both trout populations in the autumn, with no seasonal variation in prevalence. The parasite was more abundant in male than female trout (n=75, p<0.01). Analysis of the spatial distribution of the parasite across various sampling sites along the river showed the lowest prevalence and abundance of parasitic infections at the most downstream sampling site, which may reflect the predominance of female fish there and/or the smaller population of intermediate hosts. To provide the first molecular insights into D. truttae, we analysed sequences at three marker loci: the 18S rRNA gene, the cytochrome c oxidase subunit 1 (COI) gene and the internal transcribed spacer region. Phylogenetic analysis based on 18S rRNA confirmed the taxonomic grouping of D. truttae in the Illiosentidae family, first made more than 50 years ago based on morphology. The COI haplotype network did not show discrete genetic clusters corresponding to the different sampling sites, suggesting a stable population. These insights into D. truttae haplotype frequency distribution and intrapopulation genetic variation revealed minimal genetic variability, compared to the other acanthocephalan species.