Phylogenetic and morphometric relationships between two species of genus Auxis from the South China Sea and Java Sea HABIB Ahasan 1, 2 *, SULAIMAN Zohrah 1, 3 1 Environmental and Life Sciences Programme, Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku, Gadong BE 1410, Brunei Darussalam 2 Department of Fisheries and Marine Science, Noakhali Science and Technology University, Sonapur-3814, Noakhali, Bangladesh 3 Universiti Teknologi Brunei, Jalan Tungku, Gadong BE 1410, Brunei Darussalam Received 28 September 2014; accepted 22 December 2015 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2016 Abstract This study was aimed at examining the phylogenetic and morphometric relationship of frigate tuna (Auxis thazard) and bullet tuna (Auxis rochei) using mtDNA D-loop (control) region sequences and truss measurements, respectively. Maximum-likelihood (ML) tree and median-joining network showed that haplotypes from Auxis populations grouped separately. Discriminant function analyses and non-metric multidimensional scaling of morphometric data showed that bullet and frigate tuna were differed mainly with respect to truss measurements on the anterior region, suggesting adaptation to different diets available in different environments. Historic demographic analyses of sequence data showed that both bullet and frigate tuna had not undergone a significant sudden population expansion recently. Non-significant value of Tajimas’s D and Fu’s F S were indicated an effective large and stable population size for longer period of both species in South China Sea and Java Sea species. This study gives first report on the complementary relationship between morphometric and genetic analysis in stock discrimination of genus Auxis. Key words: phylogenetic relationship, mtDNA D-loop, morphometric analysis, Auxis thazard, Auxis rochei Citation: Habib Ahasan, Sulaiman Zohrah. 2016. Phylogenetic and morphometric relationships between two species of genus Auxis from the South China Sea and Java Sea. Acta Oceanologica Sinica, 35(10): 76–82, doi: 10.1007/s13131-016-0915-9 1  Introduction Tuna species are renowned for their high global economic value particularly well-known by the sashimi market (Guizani et al., 2005). The species, which the paper focuses, are for canned market. Two most commonly reported tuna in the Asian seas are the frigate tuna (Auxis thazard, Lacepede, 1800) and the bullet tuna (Auxis rochei, Risso, 1810). The frigate tuna has an ecologic- al range within the top 50 m of warm waters overlying the contin- ental shelf of the Pacific, Atlantic and Indian Oceans (Collette and Nauen, 1983; Kumar et al., 2012). The bullet tuna is highly migratory in nature and traverses within the top 10 m of the wa- ter in the Atlantic, Indian and Pacific including the Mediter- ranean Sea (Collette and Aadland, 1996). Morphologically, they are differentiated generally by the width of corselet under the ori- gin of the second dorsal fin and by the anterior extent of the dorsal scaleless area above the pectoral fin. There has been no catch record of bullet tuna from Brunei waters (DOF, 2012). In in- shore area, bullet and frigate tunas observed during September to December of each year (Muthiah, 1985). Molecular genotyp- ing study of Anisakis larvae was performed from bullet tuna in the Javanese waters (Palm et al., 2008). It indicates the presence of bullet tuna in the Java Sea. Other genetic studies of bullet and frigate tuna were conducted in the Indian waters (Kumar et al., 2012, 2013) and population dynamics of frigate tuna was investig- ated in Indian waters (Ghosh et al., 2012). Recent work involving both morphological and molecular studies was on small flat- fishes (Wang et al., 2014). Although, both frigate and bullet tunas play a very vital role for commercial fisheries throughout the world (Catanese et al., 2008), there has been no available inform- ation on both genetic and morphometric studies on bullet and frigate tuna in Brunei and Indonesian waters. Kumar et al. (2013) reported evolutionary history and phylogenetic relationship between Auxis species in Indian waters, inferred from COI se- quence. Morphometric features are classical tools widely applied in identification of stocks by highlighting morphological (or pheno- typic) variations between populations (Amin et al., 2010; Darlina et al., 2011). Information on genetic structure of local fauna was used to address varying complexities concerning wild popula- tions detecting levels of genetic variation critical for conservation strategies and sustained existence of populations (Reed et al., 2002). mtDNA was used in the present study as it is more sensit- ive to demographic events that may affect genetic variation, such as reduction in population size and geographic isolation (Dur- and et al., 2005). The present study was aimed to determine the phylogenetic relationship, demographic history between Auxis spp. based on D-loop (control) region sequences of mitochondrial DNA and morphometric analysis. In addition, this study would provide useful demographic history for understanding the population ex- Acta Oceanol. Sin., 2016, Vol. 35, No. 10, P. 76–82 DOI: 10.1007/s13131-016-0915-9 http://www.hyxb.org.cn E-mail: hyxbe@263.net *Corresponding author, E-mail: habibuit@gmail.com