Mitochondrial DNA of the Co-1 gene region was sequenced for 8 fish species (in total 17 sequences of at least 532 bp) from the far east of Russia and compared to 3 other perciform sequences, altogether comprising 20 perch-like fish sequences and 2 outgroup sequences (Cypriniformes). The analysis of the protein-coding Co-1 gene revealed a statistically substantiated bias in the (T+C):(A+G) content, confirming the basic findings on the pyrimidines-prunes ratio. The average scores of p-distances for different scales of the evolutionary history of the Co-1 gene revealed a pattern of increased nucleotide diversity at 4 different levels: (1) intraspecies, (2) intragenus, (3) intrafamily and (4) intraorder. The scores of the average p-distances of the 4 categories of comparison were: (1) 0.11 ± 0.04%, (2) 1.87 ± 0.68%, (3) 12.67 ± 0.28%, and (4) 16.52 ± 0.10%, respectively (mean ± SE). These data support the concept that speciation in the order Perciformes in most cases follows a geographic mode through accumulation of numerous small genetic changes over a long time. The phylogenetic trees for 18 and 21 sequences of perch-like fishes together with 2 other fishes belonging to the ray-finned fishes (Actinopterygii) were developed using the Co-1 gene and 4 different analytical approaches: neighbour-joining (NJ), maximum likelihood (ML), Bayesian (BA) and maximum parsimony (MP). The analysis revealed a monophyletic origin for the representatives of the Stichaeidae, which was the principal percoid family investigated (86, 96 and 100% support in our NJ, ML and BA analyses, respectively). Species identification on a per individual basis or Co-1-based DNA barcoding was high.

The complete mitochondrial genome of Stichaeus grigorjewi (Zoarcales: Stichaeidae) was sequenced for the first time based on the 27 pairs of newly designed primers using Sanger dideoxy sequencing method. Genome structure is consistent with standard scheme known for the vertebrates including 13 gene fragments, two rRNAs, 22 tRNAs, and control region. Moreover, it has additional tRNAs with atypical codons. These features were previously found in Xiphister atropurpureus, which shows the closest position to S. grigorjewi as seen from the phylogram built on the sequences of complete mitochondrial genome.

We report on the structure and composition of the first complete mitochondrial genome of Stichaeus nozawae (typical prickleback fish (Zoarcales, Stichaeidae)), obtained by dideoxy (Sanger) sequencing technique. Genome has a classic organization with 13 genes, 2 rRNAs, control region, and 22 tRNAs, including additional tRNAs with atypical codons previously found in many eelpouts. Phylogenetic analysis confirms the species identity of S. nozawae and validate its recent divergence from S. grigorjewi with unusually low interspecific genetic distance. ARTICLE HISTORY

The taxonomy of fish in the northeast Pacific area has been recently revised using molecular genetic methods, including the development of a reference library of DNA fragments for species identification. Such libraries are the basis for the development of non-invasive, high-throughput methods for monitoring biodiversity using environmental DNA (eDNA). In order to validate this approach, we used a water eDNA metabarcoding technique based on 12S rRNA and COI mitochondrial fragments and assessed the composition of the twenty northeast Pacific fish species held in a fish tank at the Primorsky Aquarium (Vladivostok, Russia). Only the 12S fragment revealed data on fish-related operational taxonomic units (OTUs). Approximately 68% of the reads were classified into two species of the genus Oncorhynchus, whose shredded fillet is used for feeding. According to the taxonomic identification for the rest of the reads, 8 out of 20 fish species in the tank (40%) were identified unambiguously, while two species could not be identified. Ten taxa can be considered conditionally identifiable since they might be concealed behind a conflicting taxonomic identification at the genus or family level. In this case, an improvement of the reference library would provide resolution. We detected contamination, which may be related to both intra-laboratory contaminants occurring during DNA extraction and water intake supplying the fish tank.