Discrimination of Juvenile Yellowfin (Thunnus albacares) and Bigeye (T. obesus) Tunas using Mitochondrial DNA Control Region and Liver Morphology

Yellowfin tuna, Thunnus albacares (Bonnaterre, 1788) and bigeye tuna, Thunnus obesus (Lowe, 1839) are two of the most economically important tuna species in the world. However, identification of their juveniles, especially at sizes less than 40 cm, is very difficult, often leading to misidentification and miscalculation of their catch estimates. Here, we applied the mitochondrial DNA control region D-loop, a recently validated genetic marker used for identifying tuna species (Genus Thunnus), to discriminate juvenile tunas caught by purse seine and ringnet sets around fish aggregating devices (FADs) off the Southern Iloilo Peninsula in Central Philippines. We checked individual identifications using the Neighbor-Joining Method and compared results with morphometric analyses and the liver phenotype. We tested 48 specimens ranging from 13 to 31 cm fork length. Morpho-meristic analyses suggested that 12 specimens (25%) were bigeye tuna and 36 specimens (75%) were yellowfin tuna. In contrast, the genetic and liver analyses both showed that 5 specimens (10%) were bigeye tuna and 43 (90%) yellowfin tuna. This suggests that misidentification can occur even with highly stringent morpho-meristic characters and that the mtDNA control region and liver phenotype are excellent markers to discriminate juveniles of yellowfin and bigeye tunas

Sampling Site.

<p>Map of Southeast Asia showing the fish sampling site (off Southern Iloilo, Philippines) with juveniles of yellowfin and bigeye tunas shown.</p

Identification of juvenile tunas caught in Southern Iloilo, Philippines based on body morphology, liver morphology and mtDNA Control Region sequence Data (n = 48).

*<p> <i>misidentified.</i></p

Graph Ordination from Principal Component Analysis.

<p>Principal Components I and II separated juveniles of yellowfin (Upper; n = 43) and bigeye (Lower; n = 5) tunas and comparison of their liver morphologies; yellowfin (A. Itano, 2005 and B. Pedrosa-Gerasmio <i>et al.</i>, 2011) and bigeye tuna (C. Itano, 2005 and D. Pedrosa-Gerasmio <i>et al.</i>, 2011).</p

Loadings from a Principal Component Analysis of the log transformed right, middle and left lobe measurements of <i>T. albacares</i> and <i>T. obesus</i>. Variables with the highest values on principal components I and II (in asterisks) are shown.

<p>Loadings from a Principal Component Analysis of the log transformed right, middle and left lobe measurements of <i>T. albacares</i> and <i>T. obesus</i>. Variables with the highest values on principal components I and II (in asterisks) are shown.</p

Variance extracted from the 3 axes using liver measurement data.

<p>Variance extracted from the 3 axes using liver measurement data.</p

Genetic diversity, population structure and demographic history of the tropical eel Anguilla bicolor pacifica in Southeast Asia using mitochondrial DNA control region sequences

The following is the supplementary data to this article: Appendix A. Supplementary dataThe tropical catadromous eel, Anguilla bicolor pacifica, an important fishery resource in Southeast Asia, is under threat due to overexploitation (especially of its glass eel phase) and the limited information on their current genetic status which is necessary for resource management. Mitochondrial DNA (mtDNA) control region sequences, a useful marker for population genetic studies in many aquatic organisms, were used to investigate the genetic diversity, population structure and demographic history of A. bicolor pacifica in the region. A total of 151 specimens were collected from three sites in Southeast Asia, namely: Phu Yen, Vietnam (n = 48); General Santos, Philippines (n = 52); and, Palu, Indonesia (n = 51). A total of 138 haplotypes were identified using the mtDNA control region sequences. In spite of the lack of shared haplotypes, low and non-significant $F_{ST}$ values, high haplotype diversity in concurrence with relatively low nucleotide diversity, a haplotype network with no phylogeographic structuring indicate no significant genetic population structuring among the eel samples from Vietnam, Philippines and Indonesia. Population expansion of A. bicolor pacifica was also suggested based on the results of the neutrality tests, mismatch distribution analysis and Bayesian skyline plot. Taken together, a joint management strategy for A. bicolor pacifica must involve countries in Southeast Asia particularly Vietnam, Philippines and Indonesia for its sustainable use.This research received financial support from the Japan ASEAN Integration Fund Project entitled “Enhancing Sustainable Utilization and Management Scheme of Tropical Anguillid Eel Resources”