Morphological analysis
A total of 123 specimens were collected during three CHINAREs. Most of them were adults and could be directly distinguished. However, there were also some juvenile and incomplete specimens, which were difficult to identify on the basis of morphological characteristics. These specimens were identified as Limanda sp., Hippoglossoides sp., Lycodes sp., Ammodytes sp., Hemilepidotus sp. and Liparis sp., etc.
Amplification and sequencing
A total of 123 mitochondrial COⅠ gene DNA fragments were successfully amplified using primers. No stop codons, deletions or insertions were observed in any of the sequences after alignment. The length of the amplified COⅠ gene was 652 bp. The number of haplotypes identified in each species ranged from 1 to 6. Overall nucleotide frequencies were C (27.7%), T (30.8%), A (23.4%), and G (18.2%). The 123 COI sequences were deposited in the GenBank database under the accession number MW435025 - MW435147.
Species identification by phylogenetic analysis of COⅠ sequences
The phylogenetic tree constructed by the NJ method is shown in Figure 1 (different-colored bands indicate different families). The same morphological species of fish formed cohesive units. All high-quality sequences were identified by BLAST searches and comparisons in GenBank, and the similarity was higher than 98% (Table 1). A total of 39 fish species belonging to 5 orders, 10 families and 23 genera were identified through DNA barcoding analysis in this survey. Among these species, 19 species of Scorpaeniformes accounted for 48.72% of the total species. Additionally, 9 species of Perciformes accounted for 23.08% of the total number of species, and 5 species from each of Pleuronectiformes and Gadiformes accounted for 12.82% of the total number of species. The smallest number of species was found in Rajiformes, which included only one species (Figure 2). At the family level, the number of Cottidae species was largest, at 9, accounting for 23.08% of the total number of species, followed by Zoarcidae, with 8 species, accounting for 20.51%. The other eight families—Gadidae, Pleuronectidae, Psychrolutidae, Agonidae, Liparidae, Ammodytidae, Hexagrammidae, and Rajidae—accounted for smaller proportions. At the genus level, the number of species from the genus Lycodes was greatest, at 8. Based on the NJ tree, all species from the same family were clustered together, indicating that the families were all monophyletic except for Cottidae, in which Hemilepidotus papilio was sister to other genera (Figure 1); thus, the NJ analysis recovered the family Cottidae as paraphyletic.
Table 1. list of fish of the 6th, the 8th and the 9th Chinese National Arctic Research.
Scientific name from morphological identification
|
Sort by
identification /%
|
Species name from NCBI
|
No. of samples
|
Gadus chalcogrammus
|
100
|
Gadus chalcogrammus
|
4
|
Gadus macrocephalus
|
100
|
Gadus macrocephalus
|
1
|
Boreogadus saida
|
99
|
Boreogadus saida
|
29
|
Arctogadus glacialis
|
100
|
Arctogadus glacialis
|
17
|
Eleginus gracilis
|
99
|
Eleginus gracilis
|
2
|
Limanda sp
|
99
|
Limanda aspera
|
1
|
Limanda sakhalinensis
|
100
|
Limanda sakhalinensis
|
1
|
Hippoglossoides robustus
|
100
|
Hippoglossoides robustus
|
1
|
Hippoglossoides sp
|
99
|
Hippoglossoides dubius
|
2
|
Hippoglossoides robustus
|
100
|
Hippoglossoides elassodon
|
3
|
Zoarcidae sp
|
99
|
Lycodes polaris
|
1
|
Lycodes adolfi
|
99
|
Lycodes palearis
|
2
|
Lycodes pallidus
|
98
|
Lycodes pallidus
|
7
|
Lycodes seminudus
|
99
|
Lycodes seminudus
|
2
|
Lycodes adolfi
|
99
|
Lycodes adolfi
|
1
|
Lycodes brevipes
|
100
|
Lycodes brevipes
|
1
|
Lycodes lavalaei
|
99
|
Lycodes lavalaei
|
2
|
Anisarchus macrops
|
100
|
Anisarchus medius
|
4
|
Ammodytes sp
|
100
|
Ammodytes hexapterus
|
1
|
Icelus spatula
|
100
|
Icelus spiniger
|
2
|
Icelus spatula
|
99
|
Icelus spatula
|
2
|
Artediellus atlanticus
|
99
|
Myoxocephalus scorpius
|
2
|
Myoxocephalus jaok
|
99
|
Myoxocephalus jaok
|
1
|
Ulcina olrikii
|
98
|
Triglops pingelii
|
1
|
Triglops nybelini
|
100
|
Triglops nybelini
|
2
|
Artediellus atlanticus
|
100
|
Artediellus atlanticus
|
9
|
Hemilepidotus sp
|
99
|
Hemilepidotus papilio
|
1
|
Gymnocanthus detrisus
|
100
|
Gymnocanthus tricuspis
|
2
|
Cottunculus microps
|
100
|
Cottunculus microps
|
2
|
Ulcina olrikii
|
99
|
Ulcina olrikii
|
1
|
Podothecus veternus
|
99
|
Podothecus veternus
|
1
|
Leptagonus decagonus
|
100
|
Leptagonus decagonus
|
1
|
Liparis fabricii
|
100
|
Liparis fabricii
|
5
|
liparis tanakae
|
100
|
Liparis bathyarcticus
|
3
|
Liparis sp
|
99
|
Liparis gibbus
|
1
|
liparis tanakae
|
99
|
Liparis tunicatus
|
2
|
Careproctus reinhardti
|
100
|
Careproctus reinhardti
|
1
|
Hexagrammos stelleri
|
99
|
Hexagrammos stelleri
|
1
|
Amblyraja hyperborea
|
100
|
Amblyraja hyperborea
|
1
|
The NJ tree showed that the barcoding results were not all consistent with the conventional taxonomy. However, 61.54% of species were identified successfully, showing at least 98% similarity. Icelus spiniger was distinctly different from I. spatula, with specimens identified as I. spatula morphologically sharing 100% nucleotide sequence similarity with the I. spiniger reference. Hippoglossoides elassodon was identified as H. robustus morphologically but presented 100% similarity to the H. elassodon reference. In similar cases, Lycodes palearis was identified as L. adolfi, Anisarchus medius was identified as A. macrops, Myoxocephalus Scorpius was identified as Artediellus atlanticus, Triglops pingelii was identified as Ulcina olrikii, and Gymnocanthus tricuspis was identified as G. detrisus. The sequences of Liparis bathyarcticus and L. tunicatus were distinctly different from the L. tanakae references. Some juvenile fish and incomplete individuals that were initially recorded as unidentified “sp.” were identified effectively based on barcoding. Limanda sp. shared 99% nucleotide sequence similarity with the reference L. aspera, indicating that it was L. aspera. Hippoglossoides sp. was identified as H. dubius with 99% nucleotide sequence similarity. Zoarcidae sp. was identified as L. polaris with 99% nucleotide sequence similarity. Ammodytes sp. was identified as A. hexapterus with 100% nucleotide sequence similarity. Hemilepidotus sp. was identified as H. papilio with 99% nucleotide sequence similarity. Liparis sp. was identified as L. gibbus with 99% nucleotide sequence similarity.
Genetic distance and barcoding gaps
The intraspecific distances ranged from 0% to 0.35%, and the minimum interspecific distances of the species were greater than 2% except for Liparis tunicatus vs L. fabricii (1.43%), Hippoglossoides elassodon vs H. robustus (0.62%), H. elassodon vs H. dubius (0.54%), H. robustus vs H. dubius (0.54%), and Icelus spatula vs I. spiniger (0.69%). Nevertheless, the minimum interspecific distance of all species was still greater than the maximum intraspecific distances. Thus, it was obvious that there were barcode gaps in the genetic distance between intraspecific distances and interspecific distance (Figure 3).