Morphological and Molecular Identification of Dactylogyrus gobiocypris (Monogenea: Dactylogyridae) on Gills of a Model Fish, Gobiocypris rarus (Cypriniformes: Gobionidae).

The rare minnow Gobiocypris rarus is an ideal model organism for toxicological research. Dactylogyrus species are usually found on the gills of this rare minnow in laboratory farming systems. Dactylogyrid infection may change the sensibility of fish to toxicants and affect toxicological evaluations. In the present study, dactylogyrid infection was investigated, and species of Dactylogyrus collected from rare minnows were determined. Based on the observed 'D. wunderi' type anchors, with a shorter outer root and elongated inner root, and accessory piece consisting of two parts, the dactylogyrids were identified as D. gobiocypris. A partial 18S-ITS1 rDNA sequence was firstly sequenced, and the highest sequence identity (86.7%) was to D. cryptomeres. Phylogenetic analysis revealed that D. gobiocypris formed a clade with D. squameus, D. finitimus, and D. cryptomeres, all of which have been recorded in the family Gobionidae. Histopathology analysis indicated that a heavy burden of D. gobiocypris caused necrosis of gill filaments. Inflammatory responses, such as tumefaction and hyperaemia, were also observed on gills with severe dactylogyrid infection. Supplementary morphological characteristics and 18S-ITS1 rDNA sequence provided basic data for identification of this parasite species.