Historical methods of identifying, naming and classifying fishes are largely based on visible morphology. Modern taxonomic work includes analysis of a host of other traits, including internal anatomy, physiology, behavior, genes, isozymes and geography; yet morphological traits remain the cornerstone of existing taxonomic treatments. However, there are limitations to relying primarily on morphology when attempting to identify fishes during various stages of their development not considered in original treatments, or when examining fragmentary or processed remains. Even when an intact adult specimen is the subject of identification, the morphological characters and other traits used to discern species are often so subtle and complex that each taxonomist can critically identify only a segment of the global fish fauna.
Multiple taxonomic experts are ordinarily required to identify specimens from even a single biotic survey. Assembling teams of appropriate experts, and/or distributing specimens to them for identification, are both time consuming and expensive tasks. Moreover, accessing existing literature and assessing the validity and priority of various taxon names can be a challenge even for the expert taxonomist. For the non-specialist faced with an assemblage of suboptimal specimens that require species identifications in real time, no method currently exists to bring the sum total of taxonomic knowledge to bear on the problem. This fact is a major impediment to the assessment, conservation and management of global fish biodiversity.
One of the major benefits of DNA-based identifications is their fast, reliable and accurate characterization across all life stages and species. Early on, the use of DNA sequencing to survey diversity led to the recognition that libraries of reference sequences could be used for species identification in cases of morphological ambiguity, such as with larval stages. DNA, the basic code for all life forms, can be the substance that unifies biological collections of all sorts. In this respect, access to DNA sequences derived from expert-identified voucher specimens can be used to better characterize and broadly identify species. The ensuing catalog of unique genetic sequences or "DNA barcodes” conceptually unites diverse assemblages of specimens, collections and associated species information under a common registry of sequence accessions. This will enhance online access to information about species and enable a broadly applicable reference database that is essential for performing DNA-based identifications on samples of unknown identity.