Authentication of Tenualosa species in Perak River, Malaysia: application of morphological measurement and molecular analysis of partial CO1 and 16S genes to resolve species ambiguity

Malaysia possessed two species of Tenualosa sp.; the Tenualosa toli and Tenualosa macrura, which can only be found in Sarawak. Recently, samples that resembled the Tenualosa sp. were found in Perak River of Peninsular Malaysia. The absence of comprehensive study of Tenualosa sp. in Peninsular Malaysia had urged this study to be conducted to authenticate the samples found. Identification were done using morphological analysis with the integration of molecular assessment using partial genes of cytochrome c oxidase subunit 1 (CO1) and 16S rRNA. Morphological analysis of 40 samples showed the closest correlation with Tenualosa ilisha (Hamilton, 1822). However, variations were found in meristic counts and the samples were differentiated into two groups. The meristic counts also overlapped with other species of the same genus. Molecular assessments on 10 samples performed using partial CO1 and 16S rRNA genes had obtained 500-bp and 573-bp sequences respectively, that has high similarity with T. ilisha. Further genetic assessment through phylogenetic analysis showed that all 10 samples formed a monophyletic lineage with T. ilisha. However, the samples were significantly separated with others of the same species from different countries. The findings suggested that there is a possibility the samples might migrate from other countries and had experienced domestic speciation towards the local environment. The findings of this study would be useful in recognizing the potential fisheries resources. This will greatly help in planning and implementing a healthy and sustainable exploitation of this species.