Fish are the largest group of vertebrates, which exhibit a remarkable diversity of morphological attributes and biological
adaptations (Eschmeyer et al., 1998; Nelson, 2006). Species are typically circumscribed based on the presence of fixed
diagnostic morphological characters which distinguish them from other species (Wiens and Servedio, 2000). But for fishes,
there are a large number of intraspecific invariants or interspecific overlappings, so fish identification is challenging for
taxonomists when facing rich biotas. The limitations inherent in morphology-based identification systems and the dwindling
pool of taxonomists call for the molecular approach to species recognition (Steinke et al., 2009a).