Molecular Characterization and Genetic Divergence of Ichthyophthirius multifiliis Fouquet, 1876 (Ciliophora) Isolates from Korea
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Ichthyophthirius multifiliis is an obligate ectoparasite causing white spot disease in freshwater fish worldwide. Despite being considered a single species, intraspecific variations have been suggested due to its broad geographical distribution and wide host range. This study investigated the genetic diversity of I. multifiliis isolates collected from three fish species in Korea: guppy (Poecilia reticulata), rainbow trout (Oncorhynchus mykiss), and Atlantic salmon (Salmo salar). Ten isolates were collected from three locations and analyzed using concatenated mitochondrial cox-1 and nad-1b gene sequences (1,237 bp). Phylogenetic analysis revealed that isolates clustered into three distinct clades according to host species, with genetic distances ranging from 0.00 to 1.98% among Korean isolates. Guppy isolates formed an independent clade, likely introduced through the ornamental fish trade, while salmo- nid isolates clustered with Turkish rainbow trout isolates. Applying established criteria, the isolates were classified into three genotypes based on host species. This study provides the first genetic charac- terization of I. multifiliis in Korea, demonstrating significant genetic divergence among isolates and highlighting the need for large-scale sampling to understand better the global genetic diversity and epidemiology of this important fish parasite.
Abstract
Ichthyophthirius multifiliis is an obligate ectoparasite causing white spot disease in freshwater fish worldwide. Despite being considered a single species, intraspecific variations have been suggested due to its broad geographical distribution and wide host range. This study investigated the genetic diversity of I. multifiliis isolates collected from three fish species in Korea: guppy (Poecilia reticulata), rainbow trout (Oncorhynchus mykiss), and Atlantic salmon (Salmo salar). Ten isolates were collected from three locations and analyzed using concatenated mitochondrial cox-1 and nad-1b gene sequences (1,237 bp). Phylogenetic analysis revealed that isolates clustered into three distinct clades according to host species, with genetic distances ranging from 0.00 to 1.98% among Korean isolates. Guppy isolates formed an independent clade, likely introduced through the ornamental fish trade, while salmo- nid isolates clustered with Turkish rainbow trout isolates. Applying established criteria, the isolates were classified into three genotypes based on host species. This study provides the first genetic charac- terization of I. multifiliis in Korea, demonstrating significant genetic divergence among isolates and highlighting the need for large-scale sampling to understand better the global genetic diversity and epidemiology of this important fish parasite.