DNA barcoding cannot discriminate between and (Clupeiformes: Clupeidae).

, the only known freshwater sardinella in the world, is endemic to Taal Lake, Philippines. Previous studies found the Taiwan sardinella, , to be morphologically very similar to and identified it as the marine sister species of . In this study, DNA barcoding using the mitochondrial cytochrome oxidase I (COI) gene was carried out to analyze species demarcation in the genus, focusing primarily on the relationship between and . The neighbour-joining (NJ) tree that was constructed using Kimura 2-parameter (K2P) model showed a single clade for the two species with 100% bootstrap support. K2P interspecific genetic divergence ranged from 0% to 0.522%, which is clearly below the suggested 3-3.5% cutoff for species discrimination. Recombination activating gene 1 (RAG1), mitochondrial control region (CR), cytochrome b, 16S rRNA, and S7 markers were used to further validate the results. and clustered together with a bootstrap support of 99-100% in each of the NJ trees. Low interspecific genetic distances between and for all the markers except CR could be attributed to incipient allopatric speciation.