Molecular Phylogeny and Host Specificity of the LarvalEustrongylides(Nematoda: Dioctophmidae) From Freshwater Fish in China

Abstract

The nematodes Eustrongylides spp. collected from different fish species in China were examined for their intra-and interspecific evolutionary variations using the molecular markers mitochondrial cytochrome oxidase c subunit 1 (COI) gene and internal transcribed spacer (ITS) rDNA regions. The phylogenetic analysis indicated that Eustrongylides species are divided into 3 wellsupported clades. The ITS divergence between the clades suggested that clades 2 and 3 might represent the same species, whereas clade 1 represent another cryptic species. The host specificity of these nematodes was analyzed according to prevalence data, host range, and phylogenetic information. Clade 1 was found in 4 fish species, i.e., Odontobutis obscurus, Silurus asotus, Culter mongolicus, and Acanthogobius flavimanus, but was predominant in the 2 perciform species, O. obscurus and A. flavimanus. Clade 2 was found in 3 fish species, Monopterus albus, Channa argus, and Channa asiatica, but was predominant in M. albus, reported to feed primarily on oligochaetes, the first intermediate host of Eustrongylides sp. Clade 3 was found in 9 species, but its low prevalence suggests accidental infection in all species. Although the larval nematode presented low host specificity, it exhibited some host preference.

Morphological and Phylogenetic Analysis of Eustrongylides sp. and Gnathostoma spinigerum Parasitizing the Asian Swamp Eel Monopterusalbus in China

“…Few epidemiological data are available for Asian swamp eel nematode infections in China [19,34]. In the present study, 78 larval nematodes were collected from 120 Asian swamp eels captured in China and examined immediately after death.…”

“…The consensus DNA sequences obtained were compared to those deposited in the GenBank database using the basic local alignment search tool (https://blast.ncbi.nlm.nih.gov/Blast.cgi, accessed on 27 April 2021). [34]. † The primers used for ITS2 (5.8S subunit complete sequence and 28S partial sequences) amplification were obtained from Cole et al (2014) [2].…”

Eustrongylides sp. (Nematoda, Dioctophymatoidea) parasitizing Hoplias malabaricus (Actinopterygii: Erythrinidae) collected from the state of Rio de Janeiro, Brazil

“…(5'-TTGGATGATTCGGTGAGGT-3') and 28SR (5' -AACCGCTTAGTAATATGCT-3') were used to amplify the internal transcribed spacer (ITS) rDNA region (XIONG et al, 2013). PCR was carried out in a final volume of 50 μl containing a mixture of 2 μl of DNA isolate, 1.25 U of Taq polymerase (Platinum Taq DNA Polymerase, Thermo Fisher Scientific, Waltham, Massachusetts, USA), 1× PCR buffer (10 millimolar [mM] of Tris-HCl, pH 8.0; and 50mM of KCl), 2-mM of MgCl 2, 0.2 mM of deoxynucleoside triphosphate (dNTP) mixture and 0.2mM of forward and reverse primers.…”

“…A negative control (ultrapure water) was included in the PCR reaction. The amplification of parasite DNA was performed using a PTC-100® (Bio-RadLaboratories, Ltd., Hertfordshire, UK) following the cycle of the primers (XIONG et al, 2013). The PCR products were stained using GelRed TM and were viewed by means of electrophoresis on a 1.5% agarose gel.…”

“…In spite of the few ITS gene regions available for nematode species of relevance to fish parasitology, the ITS sequence of the present study was found to be similar to other Eustrongylides spp. isolates reported by Xiong et al (2013), while sequences of Capilllarinae and Trichuris formed an outergroup (Figure 6). The phylogenetic analysis performed with ITS rDNA multiple alignment supported its taxonomic position within the Eustrongylides spp.…”