Short Communication |
Corresponding author: Takaomi Arai ( takaomi.arai@ubd.edu.bn ) Academic editor: Walter Boeger
© 2021 Ahmad Fathi Norarfan, Siti Shazwani Azreena Mokti, Hussein Taha, Muhamad Amin, Muhamad Ali, Takaomi Arai.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Norarfan AF, Azreena Mokti SS, Taha H, Amin M, Ali M, Arai T (2021) DNA barcoding of a tropical anguillid eel, Anguilla bicolor (Actinopterygii: Anguilliformes), in Indo-Pacific region and notes on its population structure. Zoologia 38: 1-7. https://doi.org/10.3897/zoologia.38.e59332
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The tropical anguillid eel, Anguilla bicolor McCelland, 1844, includes two subspecies, Anguilla bicolor bicolor McCelland, 1844 and Anguilla bicolor pacifica Schmidt, 1928, and is distributed across the Indo-Pacific region. Although A. bicolor is widely distributed and recognized as an important fish resource in the Indo-Pacific region, few studies have been conducted on its genetic variation and population structure. DNA barcoding of A. bicolor specimens collected in the Indo-Pacific region was carried out in this study using mitochondrial cytochrome c oxidase subunit I. Anguilla bicolor was found to diverge genetically, which supported its classification into two different subspecies. In addition, our study showed that A. bicolor bicolor had two genetically distinct populations/groups, and these different populations co-occur geographically in Indonesia and Malaysia in the eastern Indian Ocean. Our findings suggest that the eel larvae might be transported from at least two geographically different spawning grounds in the Indian Ocean, and then recruited to and settled in the same habitats in Indonesian and Malaysian waters. The molecular evidence calls for further research on the life history, stock assessment and protection of the populations of A. bicolor bicolor in Indonesia and Malaysia.
Anguillid eel, haplotype network, molecular phylogeny, tropical species
Sixteen species of the genus Anguilla Schrank, 1798 are widely distributed across the world. Eleven species are found in tropical Indo-Pacific regions (
The short-finned tropical eel, A. bicolor, is distributed globally across the Indo-Pacific region, from East Africa to Papua New Guinea, and the Philippines through Indonesia (
Anguilla bicolor
was previously sampled across its entire geographic range and analyzed using microsatellites and mitochondrial control region sequences (
Knowledge on the life history of A. bicolor has been gradually accumulating (e.g.,
The aim of the present study was to investigate the genetic variation through DNA barcoding of A. bicolor in Indonesian, Malaysian and Philippine waters. All eel specimens were examined for their morphological characteristics and cytochrome c oxidase subunit I (COI) gene sequence. We also discuss the potential dispersion mechanism and importance of the population structure of A. bicolor in these regions.
A total of 18 anguillid eels were collected from Southeast Asia: nine specimens in Indonesia (Cilacap and Yogyakarta, central Java), four specimens in Malaysia (Penang, northwestern Peninsular Malaysia) and five specimens in the Philippines (Mindanao) through traps, hooks and lines from 2009 to 2019 (Fig.
Morphometric characteristics of tropical anguillid eels collected in Southeast Asia.
Country | Location | Year | Number of samples | Total length range (mm) | FDI range (%) | Identification by morphology | Identification by DNA barcoding |
Indonesia | Yogyakarta | 2019 | 8 | 338–449 | 0–4.7 | A. bicolor bicolor | A. bicolor bicolor |
Cilacap | 2009 | 1 | 730 | 1.0 | A. bicolor bicolor | A. bicolor bicolor | |
Malaysia | Penang | 2015 | 4 | 342–412 | -0.3–2.0 | A. bicolor bicolor | A. bicolor bicolor |
Philippines | Mindanao | 2019 | 5 | 112–124 | 0.7–2.5 | A. bicolor pacifica | A. bicolor pacifica |
Map of sampling locations of Anguilla bicolor bicolor from Indonesia and Malaysia and A. bicolor pacifica from the Philippines. Sampling locations are shown in red. Locations of Banda Aceh in northern Sumatra of Indonesia, Sukabumi in western Java of Indonesia, Andhra Pradesh in southeast India, Langkawi and Penang islands of northwest Peninsular Malaysia, Cebu in the Philippines, and Yangon of Myanmar, which were used in molecular phylogenetic and haplotype network analyses, are shown in blue. Base map is downloaded from http://viewer.nationalmap.gov/viewer (
DNeasy Blood & Tissue Kit (QIAGEN, Germany) was used to extract genomic DNA from a dorsal fin clip. Approximately 600 bp region of the mitochondrial COI gene was amplified using different combinations of universal primers: FishF1 (5’TCA ACC AAC CAC AAA GAC ATT GGC AC3’), FishF2 (5’TCG ACT AAT CAT AAA GAT ATC GGC AC3’), FishR1 (5’TAG ACT TCT GGG TGG CCA AAG AAT CA3’), and FishR2 (5’ACT TCA GGG TGA CCG AAG AAT CAG AA3’) (
MEGA version X (
GUIDANCE version 2 (
Eighteen eel samples had short dorsal fin and skin without variegated markings. All the eel samples had FDI values of -0.3 to 4.7 % (Table
DNA barcoding using the COI gene confirmed that the 13 specimens from Indonesia and Malaysia and five specimens from the Philippines were A. bicolor bicolor and A. bicolor pacifica, respectively (Table
From our phylogenetic analyses (Fig.
Haplotype analysis revealed a total of 18 different haplotypes in A. bicolor bicolor (H1 – H18 in Fig.
Maximum Parsimony tree using the COI gene sequences of Anguilla bicolor bicolor and Anguilla bicolor pacifica and additional sequences obtained from the GenBank database with indicated accession numbers. Anguilla megastoma was used as outgroup. The consistency index is 0.73, the retention index is 0.93, and the composite index is 0.82 for all sites and 0.68 for parsimony-informative sites. The percentages of the bootstrap test for Maximum Parsimony/Neighbour Joining/Maximum Likelihood are shown next to the branches.
Haplotype network constructed with Anguilla bicolor COI gene sequences. Each colour represents a sample site. The size of the circle is proportional to the number of samples that belong to each haplotype. White circle refers to median vector which is a hypothesized or missing haplotype. Each dash, which appears on the line that connects two haplotypes together, symbolizes one mutational step.
Anguilla bicolor
from the Indian Ocean (A. bicolor bicolor) and Pacific Ocean (A. bicolor pacifica) were found to diverge from each other, and the outcomes of our COI gene sequence were similar to those previous studies using microsatellites, mitochondrial control region and cytochrome b sequences (
Based on the COI sequence analysis, the results suggest that different A. bicolor bicolor populations could co-occur geographically in Indonesian and Malaysian waters. Spawning areas of A. bicolor bicolor are thought to be located in the waters off west Sumatra (
Anguilla bicolor bicolor
in the eastern Indian Ocean has a longer leptocephalus period (119–171 days) (
The specific choice of spawning area might be imprinted in anguillid eels including A. bicolor bicolor, although there is no physical barrier to migration to the different spawning areas. The occurrence of two populations in the eastern Indian Ocean suggests that population divergence in anguillid eels could still occur even in the absence of physical barriers during the spawning migration.
This study focused only in the eastern side but did not include the western side of Indian Ocean. The sample sizes were also small in all localities. Therefore, more comprehensive research is needed to understand the population structure of A. bicolor bicolor across the Indian Ocean. This study has revealed a unique population structure in A. bicolor bicolor, revealing a clear genetic divergence in the eastern Indian Ocean. The molecular evidence calls for further research on the life history, stock assessment and protection of the populations of A. bicolor bicolor in Indonesia and Malaysia.
This study was financially supported by University Brunei Darussalam under the Competitive Research Grant Scheme (UBD/OVACRI/CRGWG(003)) and under the Faculty/Institute/Center Research Grant (UBD/RSCH/1.4/FICBF(b)/2019/021 and UBD/RSCH/1.4/FICBF(b)/2020/029).