Morphological and molecular characterization of Eustrongylides excisus larvae (Nematoda: Dioctophymatidae) in Sander lucioperca (L.) from Northern Turkey.

The genus Eustrongylides Jägerskiöld, 1909 includes parasitic nematodes (Dioctophymatidae) affecting various fish species and piscivorous birds of freshwater ecosystems. Currently, there is little information on the molecular characterization of E. excisus based on nuclear ribosomal internal transcribed spacer (ITS) rDNA regions. However, before the present study, there had been no reports of characterizing the E. excisus using nuclear small subunit ribosomal RNA (SSU rRNA) and mitochondrial cytochrome c oxidase subunit I (COI) genes sequences. In the present study, Eustrongylides spp. larvae were collected from pike-perch Sander lucioperca (L.) in Northern Turkey, and characterized by sequencing of ITS regions, SSU rRNA, and COI markers. Larvae herein morphologically identified as the fourth stage of Eustrongylides spp. were genetically identified as E. excisus based on the ITS sequence analysis. This study is the first record of SSU rRNA and COI sequences for E. excisus in GenBank. This is also a molecular characterization of E. excisus for the first time in Turkey. The ITS, SSU rRNA, and COI sequences of E. excisus can be used to establish the phylogenetic relationships of Eustrongylides species from Turkey and worldwide for further studies.