Abstract
Diplostomum species metacercariae are trematode parasites that pose serious economic threats to aquaculture practice globally. Identification of Diplostomum at metacercariae stage has remained equivocal, hence lack of elucidation of the actual role of these species in fish population. 21 Diplostomoid metacercariae obtained from eyes of Nile tilapia were characterized using 18S and ITS rDNA (ITS1-5.8S-ITS2) genes. Phylogenetic analyses of ITS rDNA gene dataset in the metacercariae revealed close relationship to Diplostomum mashonense and D. baeri. Molecular identification using 18S rDNA sequences revealed close relationship to D. compactum, D. phoxini and D. spathaceum. Overall, genetic analyses in this study depicted a significant unrecognized genetic diversity among Diplostomum species. Successful differentiation of Diplostomum genera in this study using ribosomal markers suggested that 18S and ITS rDNA genes are effective genetic markers for inter-species phylogenetic analysis and should be employed in future for identification of diplostomoidea.
Highlights
Diplostomum metacercariae are trematode parasites with complex three host lifecycle that are considered major pathogens of fish
Diplostomum parasites have been encountered in fish farms in the northern hemisphere (Europe and North America) and as such received wide theoretical and empirical attention due to their pathogenic consequences to fingerlings [3,4,5,6]
Kisumu region was preferred for the study because of the Economic Stimulus Program (ESP) initiated by the government in 2009 that targeted fish farmers in the region and led to the construction of over 300 fish ponds in the municipality
Summary
Diplostomum metacercariae are trematode parasites with complex three host lifecycle that are considered major pathogens of fish They mature in the small intestine of piscivorous birds and are passed on to snails as first intermediate host and fish as second intermediate host during their life cycle [1]. Taxonomic studies on the diplostomid digeneans from the African continent are scarce and limited to few Diplostomum species descriptions published between 1930s-1960s, and virtually little is known of their natural history [e.g., 11,12]. This is related to low sampling efforts in tropical countries due to lack of expertise in the field of fish parasitology. Identification of these parasites is problematic due to 1) the presence of morphologically similar species; 2) the phenotypic plasticity of the adults and metacercariae; 3) the simple larval morphology; and 4) the difficulties in linking life-cycle stages [13]
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