Complete mitochondrial genome of ocellated blenny, Opisthocentrus ocellatus (Tilesius, 1811) (Zoarcales: Opisthocentidae)

Abstract

The complete mitochondrial genome (mitogenome) of Opisthocentrus ocellatus (Zoarcales: Opisthocentridae) was sequenced for the first time. The whole genome was 16,525 bp in length and contained 13 protein-coding genes, 22 transfer RNA genes (tRNA), two ribosome (rRNA) genes, and two non-coding regions. The overall base composition of the mitochondrial DNA (mtDNA) was 26.2% for A, 28.3% for T, 27.4% for C, and 18.1% for G. Six protein-coding genes include incomplete stop codons while others have standard ones, and start codons are typically ATG, GTG, ATA, or ATC. The phylogenetic analysis, which based on the mitogenomes of O. ocellatus and other 14 fish species from Zoarcales infraorder indicated that O. ocellatus is more closely related to the family Pholidae than to Stichaeidae.

Keywords:

• mitogenome
• phylogenetic analysis

The ocellated blenny, Opisthocentrus ocellatus, is one of common species of the recently established family Opisthocentridae (Teleostei: Perciformes: Zoarcales) (Radchenko 2015; Fricke et al. 2018). Although of no commercial value, it is usual in nearshore waters. The ocellated blenny is a typical representative of food chains in boreal communities, dwelling in algae and rocky nearshore habitats, usually at a depth of less than 70 m (Mecklenburg and Sheiko 2004). Its range includes the following areas of the North Western Pacific: the western Bering Sea, Sea of Okhotsk, coastal waters of the Sea of Japan and Korean Peninsula. The O. ocellatus has been long assigned to the pricklebacks subfamily Opisthocentrinae (Makushok 1958; Parin et al. 2014). However, following Radchenko (Radchenko 2015), based on the comparative molecular phylogenetic analysis of several mitochondrial and nuclear loci, also taking into account morphological traits, the subfamily was raised to family rank (Fricke et al. 2018). However, this conclusion is still controversial, the scientific literature and particularly the GenBank Taxonomy Browser still list O. ocellatus in pricklebacks (Stichaeidae) family.

To increase the power of the molecular taxonomy resolution of Opisthocentrus and examine its position within Zoarcales, the mitogenome of O. ocellatus (GenBank accession number MK568985, voucher number MIMB 37599) from Peter the Great Bay (the Vostok Bay; 42.89°N, 132.73°E) of the Sea of Japan collected in May 20, 2017 was determined using dideoxy sequencing technique. Using Sliding Window-Based PSO Algorithm (Yang et al. 2011) 27 pars of primers were designed based on the sequences available in GenBank for Zoarcoids. The resulted chromatograms were assembled into mitogenome fragments using Geneious Trial (Kearse et al. 2012). Then the produced consensus sequence of complete genome was annotated using MitoAnnotator online pipeline (Iwasaki et al. 2013) and MITOS Web Server (Bernt et al. 2013).The sequences were aligned by Muscle (Edgar 2004) implemented in MEGA 7.0 (Kumar et al. 2016) and the TrN + G + I substitution model was chosen as the best for phylogenetic analysis.

The mitogenome of O. ocellatus comprised 16,525 bp in length, including 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and two noncoding regions (CR or D-loop and origin of L-strand replication or OL) which is in accordance with the mitogenomes of the typical ray-fined fish (Kartavtsev et al. 2007; Satoh et al. 2016). The CR of O. ocellatus located between the tRNA^Pro and the tRNA^Phe genes and is determined to be 850 bp in length. The putative OL is placed in the WANCY region between tRNA^Asn and tRNA^Cys with 39 bp in length. Eight tRNAs (tRNA^Gln, tRNA^Ala, tRNA^Asn, tRNA^Cys, tRNA^Tyr, tRNA^Ser, tRNA^Pro, tRNA^Glu) and ND6 are conventionally located on the light strand (L-strand), whereas all of the remaining genes were on the heavy strand (H-strand). The overall base composition of H-strand is 26.6% A, 27.5% T, 18.1% G, and 27.4% C. All 13 genes start with the ATG initiation codon except COI, which initiates with GTG, while ND2 and ND3 terminate with ATA and ATC, respectively. Incomplete stop codons were revealed in ND2, ND3, ND4, COII, ATPase 6, and Cyt-b genes. The atypical stop codons were also found in many other zoacids fishes, such as Stichaeus grigorjewi (Turanov et al. 2019), Lycodes brevipes (Li et al. 2019), Lycodes ygreknotatus (Zheng et al. 2019), X. Atropurpureus (Group et al. 2017), and in other taxa (Kartavtsev et al. 2007; Satoh et al. 2016).

In order to investigate the phylogenetic position of O. ocellatus among nearest relatives, neighbour-joining and maximum likelihood phylogenetic analyses were carried out based on complete mitogenome sequences from 14 fish species of Zoarcales infraorder together with Aulicthys japonicus (Cottioidei, Perciformes) as an outgroup. As shown in Figure 1, O. ocellatus is more closely related to the family of Pholidae then to Stichaeidae, as well as other families within eelpouts.

Figure 1. NJ-phylogenetic tree demonstrating the relationships among Zoarcoid fishes built on complete sequences of mitochondrial genome. Numbers in nodes indicate support values based on 1000 replicates of non-parametric bootstrap test in order NJ/ML.

Disclosure statement

The authors have no conflicts of interest to declare. The authors are solely responsible for the content and the writing of this paper.

Additional information

Funding

This research was supported by Far Eastern Branch of the Russian Academy of Sciences in the framework of the Federal Program of Base Research (#18-4-040).